Sharp-tailed Snake (Contia tenuis): COSEWIC assessment and status report on the Pacific Coast and Coast Mountains populations in Canada 2021

Official title: COSEWIC Assessment and Status Report on the Sharp-tailed Snake (Contia tenuis) Pacific Coast and Coast Mountains populations in Canada

Committee on the Status of Endangered Wildlife in Canada (COSEWIC)
Pacific Coast population – Threatened 2021
Coast Mountains population – Endangered 2021

COSEWIC assessment summary

Assessment summary – November 2021 (Pacific Coast population)

Common name: Sharp-tailed Snake - Pacific Coast population

Scientific name: Contia tenuis

Status: Threatened

Reason for designation: The Canadian distribution of this tiny snake is confined to a small area in southeastern Vancouver Island and the southern Gulf Islands of British Columbia. Increased search effort since the last assessment has resulted in the documenting of five previously unrecorded subpopulations, extending the known range. The number of mature individuals is thought to be ~12,000. These snakes continue to face threats from introduced species, ongoing development, off-trail recreation, habitat fragmentation by roads, and increasing droughts associated with climate change. The explosive growth of the introduced invasive Common Wall Lizard in recent years is of concern; these lizards may prey on eggs and hatchling snakes and have the potential to eliminate or greatly reduce some subpopulations in the near future. Re-evaluation of the degree of population fragmentation and better understanding of the snakes’ distribution and abundance contributed to the change in status from Endangered to Threatened.

Occurrence: British Columbia

Status history: Designated Endangered in April 1999. Status re-examined and confirmed in October 1999 and November 2009. Status re-examined and designated Threatened in December 2021.

Assessment summary – November 2021 (Coast Mountains population)

Common name: Sharp-tailed Snake - Coast Mountains population

Scientific name: Contia tenuis

Status: Endangered

Reason for designation: The Canadian distribution of this tiny snake is confined to a small area of the Pemberton Valley in the southwestern interior of British Columbia. First documented in 2011, this population represents the only confirmed occurrence of the species in mainland Canada. The population is thought to be small (~345 mature individuals, based on extrapolation from Vancouver Island densities), although no accurate estimates are available. Since this population was documented, its habitat has declined due to ongoing urban development. Other threats include off-trail recreation, gravel extraction, habitat fragmentation by roads, and storms and flooding associated with climate change. Small population size, restricted distribution, and inferred and projected continuing population decline from multiple threats contributed to the Endangered status.

Occurrence: British Columbia

Status history: Designated Endangered in December 2021.

COSEWIC executive summary

Sharp-tailed Snake
Contia tenuis

Pacific Coast population
Coast Mountains population

Wildlife species description and significance

Sharp-tailed Snake, Contia tenuis, is a small, slender snake with a total length of adults usually less than 34 cm. Distinguishing features include unkeeled scales that give the snake a smooth appearance, solid dorsal colouration, and lack of prominent longitudinal stripes in adults. Distinctive black and white barring on the underside and a thorn-like scale at the tip of the tail are diagnostic. As one of only two species of the genus Contia, the species has scientific significance for evolutionary studies. On the coast, the species is a component of rare Garry Oak and Arbutus ecosystems.

Distribution

The global distribution of Sharp-tailed Snake extends from southwestern British Columbia to the central coast of California. In Canada, the species has been recorded from southern Vancouver Island, southern Gulf Islands in the Strait of Georgia (North and South Pender, Saltspring, and Galiano), and Pemberton Valley in mainland British Columbia, where it was discovered in 2011. The disjunct, relict Pemberton Valley population is at the northernmost extent of the species’ range. Unique local adaptations are likely due to its long (thousands of years) isolation from its coastal counterparts, harsh climate, and distinct habitats. Two designatable units are therefore proposed: Pacific Coast population, including all island subpopulations, and Coast Mountains population, including the Pemberton Valley snakes.

Habitat

Sharp-tailed Snake inhabits low elevation, open-canopy woodlands dominated by Douglas-fir; Arbutus and/or Garry Oak are usually also present along the coast. The snakes are often found in or near forest openings on rocky outcrops and hillsides. Such habitats are naturally fragmented, which is exacerbated by human habitation, roads, and other developments. Occupied sites usually have good exposure to sun, shallow soil and leaf litter, and a large cover of rock. Rocky slopes with southern exposure provide warm microhabitats required for egg-laying and thermoregulation and are also used for hibernation. Such sites are exceedingly important and may be a limiting resource at the species’ northern distributional limits. Available information suggests that individual snakes occur in approximately the same areas year-round with only minor seasonal shifts in habitat use; there is no evidence of long-range migratory movements, such as recorded for many larger snakes in temperate regions.

Biology

Sharp-tailed Snake is secretive and spends much of its time underground, making it difficult to find and study. Along the coast, the species has been detected in all months of the year, but surface activity peaks during the relatively cool periods in spring and fall; some activity also takes place on warm summer nights, especially after rain. In Pemberton, seasonal activity is limited by long cold periods in winter and high temperatures in summer. The diet is thought to consist mostly of slugs, including introduced species. Females lay a clutch of about three to five eggs, and young may take two to three years to mature, as reported for other small snakes. Individual Sharp-tailed Snakes can live nine years or more, and generation time is estimated to be five to seven years.

Population sizes and trends

The Pacific Coast population is estimated at roughly 12,000 and the Coast Mountains population at 350 mature individuals, based on recorded densities at a Vancouver Island site monitored intensively for 8 years. These values represent minimum estimates because the area of occupancy is incompletely known at most sites, and population size could not be estimated for three coastal wilderness sites that contain relatively large areas of unsurveyed habitat.

Population trends are unknown, but a continuing decline is inferred and projected from habitat trends and threats. In particular, loss of high-quality habitat has been documented over the past decade in Langford, Vancouver Island, and in Pemberton. The species continues to persist at most known sites, but there have been no further observations from Galiano Island since the original sighting in 1981.

Threats and limiting factors

The rarity of Sharp-tailed Snake in Canada is likely due to climatic and historical factors. The species exists at the northern limits of its range in southern British Columbia, and present-day populations are probably relicts from a more extensive past distribution. Habitat loss, degradation, and fragmentation due to housing and other developments pose major threats to both Pacific Coast and Coast Mountains populations. Invasive species, particularly Common Wall Lizard, pose an additional threat to the Pacific Coast population. Expanding road networks and high intensity off-trail recreational activities are threats at some sites. Summer droughts, predicted to increase in frequency and duration due to climate change, are a pervasive threat across the species’ Canadian range, but climate change may also positively affect the species by increasing thermoregulation opportunities at the northern extremity of its range.

Protection, status and ranks

Under Canada’s Species at Risk Act, Sharp-tailed Snake is listed as Endangered and is on Schedule 1, the official list of wildlife species at risk. A recovery strategy has been prepared, and a total 552.68 ha of Critical Habitat, distributed across the species’ Canadian distribution, has been delineated. Records of the species exist from five federal lands, where the provisions of the Act are currently implemented. The species also occurs in several regional and municipal parks, where development on its habitat is limited. In the Gulf Islands, the majority of occupied sites are on unprotected private lands. In Pemberton Valley, the species occurs mostly on unprotected private and public lands. The Wildlife Act of British Columbia prohibits the collection, handling, and trade of all native wildlife species, including Sharp-tailed Snake, without a permit.

Technical summary - Pacific Coast population

Contia tenuis
Sharp-tailed Snake - Pacific Coast population
Couleuvre à queue pointue - Population de la côte du Pacifique
Range of occurrence in Canada (province/territory/ocean): British Columbia

Demographic information

Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines (2011) is being used)

-5-7 years, based on IUCN (2011) method

Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?

Yes, inferred and projected decline based on habitat loss (Mill Hill) and ongoing threats

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations, whichever is longer up to a maximum of 100 years]

unknown

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

unknown

[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

10-70% suspected decline, based on threats calculator results (“high” threat impact)

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any period [10 years, or 3 generations, whichever is longer up to a maximum of 100 years], including both the past and the future.

unknown

Are the causes of the decline a. clearly reversible and b. understood and c. ceased?

a. no
b. yes (habitat loss and fragmentation mainly from development and roads)
c. no

Are there extreme fluctuations in number of mature individuals?

no

Extent and occupancy information

Estimated extent of occurrence (EOO)

1,839 km² calculated based on minimum convex polygon around known occurrences, within Canada’s extent of jurisdiction

Index of area of occupancy (IAO)(Always report 2x2 grid value).

112 km²

Is the population “severely fragmented” i.e., is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

a. possibly if threat from invasive Wall Lizards impacts viability of largest subpopulations substantially
b. yes, due to natural fragmentation of habitat and barriers to movements

Number of “locations”^* (use plausible range to reflect uncertainty if appropriate)

7-11, based on threat from rapidly expanding invasive European Wall Lizard populations

Is there an [observed, inferred, or projected] decline in extent of occurrence?

no, known EOO has increased due to search effort; actual EOO has not changed

Is there an [observed, inferred, or projected] decline in index of area of occupancy?

no, known IAO has increased due to search effort; actual IAO has not changed

Is there an [observed, inferred, or projected] decline in number of subpopulations?

no, known subpopulations have increased due to search effort; no change in actual number of subpopulations

Is there an [observed, inferred, or projected] decline in number of “locations”*?

no

Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat?

yes, observed and projected decline in area, extent, and quality of habitat (see Threats)

Are there extreme fluctuations in number of subpopulations?

no

Are there extreme fluctuations in number of “locations”^*?

no

Are there extreme fluctuations in extent of occurrence?

no

Are there extreme fluctuations in index of area of occupancy?

No

^* See Definitions and Abbreviations on COSEWIC website and IUCN for more information on this term.

Number of mature individuals (in each subpopulation)

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations whichever is longer up to a maximum of 100 years, or 10% within 100 years]? Not done due to lack of data

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes, in May 2020. Overall threat impact “high”

Key threats (IUCN threat #) were identified as:

• residential and commercial development – medium impact (1)
• invasive and other problematic species – medium to low impact (8)
• transportation and service corridors – low impact (4)
• human intrusions and disturbance – low impact (6)
• natural system modifications – low impact (7)
• climate change and severe weather – low impact (11)
• pollution – Unknown impact (9)

What additional limiting factors are relevant?

• low reproductive potential and slow ability to recover from perturbations
• habitat specificity and natural fragmentation of habitats, exacerbated by human developments

Rescue effect (immigration from outside Canada)

Status of outside population(s) most likely to provide immigrants to Canada.

Washington State: S3 (Vulnerable)

Is immigration known or possible?

no, separated from USA populations by stretches of ocean

Would immigrants be adapted to survive in Canada?

yes

Is there sufficient habitat for immigrants in Canada?

unknown

Are conditions deteriorating in Canada?⁺

yes

Are conditions for the source (i.e., outside) population deteriorating?⁺

yes

Is the Canadian population considered to be a sink?⁺

no

Is rescue from outside populations likely?

no

⁺ See Table 3 (Guidelines for modifying status assessment based on rescue effect).

Data sensitive species

Is this a data sensitive species? Yes in British Columbia; COSEWIC: No

Status history

COSEWIC Status History: Designated Endangered in April 1999. Status re-examined and confirmed in October 1999 and November 2009. Status re-examined and designated Threatened in December 2021.

Status and reasons for designation

Status: Threatened

Alpha-numeric codes: B1ab(iii,v)+2ab(iii,v)

Reasons for designation: The Canadian distribution of this tiny snake is confined to a small area in southeastern Vancouver Island and the southern Gulf Islands of British Columbia. Increased search effort since the last assessment has resulted in the documenting of five previously unrecorded subpopulations, extending the known range. The number of mature individuals is thought to be ~12,000. These snakes continue to face threats from introduced species, ongoing development, off-trail recreation, habitat fragmentation by roads, and increasing droughts associated with climate change. The explosive growth of the introduced invasive Common Wall Lizard in recent years is of concern; these lizards may prey on eggs and hatchling snakes and have the potential to eliminate or greatly reduce some subpopulations in the near future. Re-evaluation of the degree of population fragmentation and better understanding of the snakes’ distribution and abundance contributed to the change in status from Endangered to Threatened.

Applicability of criteria

Criterion A (Decline in Total Number of Mature individuals): Not applicable. Insufficient data to reliably infer, project, or suspect population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Meets Threatened, B1ab(iii,v)+B2ab(iii,v), because EOO 1,839 km² and IAO 112 km² respectively are both below thresholds for Threatened, the population (a) exists at 10 or fewer locations, and (b) is experiencing a (iii) continuing observed decline in extent and quality of habitat, and (v) projected decline in number of mature individuals.

Criterion C (Small and Declining Number of Mature individuals): Not applicable. Number of mature individuals is ~12,000, exceeding threshold for Threatened.

Criterion D (Very Small or Restricted Population): Not applicable. Number of mature individuals is ~12,000, exceeding threshold for Threatened.

Criterion E (Quantitative Analysis): Not applicable. Analysis not conducted.

Technical summary - Coast Mountains population

Contia tenuis
Sharp-tailed Snake - Coast Mountains population
Couleuvre à queue pointue - Population de la chaîne Côtière
Range of occurrence in Canada (province/territory/ocean): British Columbia

Demographic information

Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines (2011) is being used)

-5-7 yrs, based on IUCN (2014) method

Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?

yes, inferred and projected decline based on habitat loss from subdivision development in 2016 and ongoing threats

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations, whichever is longer up to a maximum of 100 years]

unknown

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

unknown

[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

10-70% suspected, based on threats calculator results (“high” threat impact)

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any period [10 years, or 3 generations, whichever is longer up to a maximum of 100 years], including both the past and the future.

unknown

Are the causes of the decline a. clearly reversible and b. understood and c. ceased?

a. no
b. yes (habitat loss and fragmentation mainly from development and roads)
c. no

Are there extreme fluctuations in number of mature individuals?

no

Extent and occupancy information

Estimated extent of occurrence (EOO)

12 km²; minimum convex polygon around known occurrences is 1.11 km², but adjusted to 12 km² because by definition EOO cannot be smaller than IAO

Index of area of occupancy (IAO) (Always report 2x2 grid value).

12 km²

Is the population “severely fragmented” i.e., is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

a. n/a
b. n/a
Only one subpopulation is known, so the concept does not apply

Number of “locations”^* (use plausible range to reflect uncertainty if appropriate)

2-4, based on threat from projected housing developments and from increasing recreational activity within the remainder of the range

Is there an [observed, inferred, or projected] decline in extent of occurrence?

unknown (population discovered only recently, in 2011)

Is there an [observed, inferred, or projected] decline in index of area of occupancy?

unknown (population discovered only recently, in 2011)

Is there an [observed, inferred, or projected] decline in number of subpopulations?

n/a

Is there an [observed, inferred, or projected] decline in number of “locations”*?

yes, projected decline due to subdivision development

Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat?

yes, observed and projected decline in area, extent, and quality of habitat

Are there extreme fluctuations in number of subpopulations?

no

Are there extreme fluctuations in number of “locations”^*?

no

Are there extreme fluctuations in extent of occurrence?

no

Are there extreme fluctuations in index of area of occupancy?

no

^* See Definitions and Abbreviations on COSEWIC website and IUCN for more information on this term.

Number of mature individuals (in each subpopulation)

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations whichever is longer up to a maximum of 100 years, or 10% within 100 years]?

Not done due to lack of data

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes, in May 2020. Overall threat impact “high”

Key threats (IUCN threat #) were identified as:

• residential and commercial development – high impact (1)
• human intrusions and disturbance – medium impact (6)
• energy production and mining – low impact (3)
• transportation and service corridors – low impact (4)
• natural system modifications – low impact (7)
• invasive and other problematic species – low impact (8)
• climate change and severe weather – low impact (11)
• pollution – Unknown impact (9)

What additional limiting factors are relevant?

• low reproductive potential and slow ability to recover from perturbations
• habitat specificity and natural fragmentation of habitats, exacerbated by human developments

Rescue effect (immigration from outside Canada)

Status of outside population(s) most likely to provide immigrants to Canada.

Washington State: S3 (Vulnerable)

Is immigration known or possible?

no, separated from USA populations by over 300 km and by developed areas on Lower Mainland of British Columbia

Would immigrants be adapted to survive in Canada?

unknown; this northernmost population may have local adaptations

Is there sufficient habitat for immigrants in Canada?

unknown

Are conditions deteriorating in Canada?⁺

yes

Are conditions for the source (i.e., outside) population deteriorating?⁺

not applicable

Is the Canadian population considered to be a sink?⁺

no

Is rescue from outside populations likely?

no

⁺ See Table 3 (Guidelines for modifying status assessment based on rescue effect).

Data sensitive species

Is this a data sensitive species? yes in British Columbia; COSEWIC no

Status history

COSEWIC Status History: Designated Endangered in December 2021.

Status and reasons for designation

Status: Endangered

Alpha-numeric codes: B1ab(iii,iv,v)+2ab(iii,iv,v); C2a(ii)

Reasons for designation: The Canadian distribution of this tiny snake is confined to a small area of the Pemberton Valley in the southwestern interior of British Columbia. First documented in 2011, this population represents the only confirmed occurrence of the species in mainland Canada. The population is thought to be small (~345 mature individuals, based on extrapolation from Vancouver Island densities), although no accurate estimates are available. Since this population was documented, its habitat has declined due to ongoing urban development. Other threats include off-trail recreation, gravel extraction, habitat fragmentation by roads, and storms and flooding associated with climate change. Small population size, restricted distribution, and inferred and projected continuing population decline from multiple threats contributed to the Endangered status.

Applicability of criteria

Criterion A (Decline in Total Number of Mature individuals): Not applicable. Insufficient data to reliably infer, project, or suspect population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Meets Endangered, B1ab(iii,iv,v)+2ab(iii,iv,v), because EOO and IAO are 12 km² (both lower than thresholds) and the population is (a) known to exist at 2-4 locations and (b) experiencing a continuing (iii) observed and projected decline in extent and quality of habitat, (iv) projected decline in number of locations, and (v) inferred and projected decline in number of mature individuals.

Criterion C (Small and Declining Number of Mature individuals): Meets Endangered, C2a(ii), as the estimated population of about 345 mature individuals is less than threshold of 2500, with an inferred and projected continuing decline and only one subpopulation.

Criterion D (Very Small or Restricted Population): Meets Threatened, D1; Estimated population of 345 is less than threshold value of 1000.

Criterion E (Quantitative Analysis): Not applicable. Analysis not conducted.

Preface

Since the previous status report (COSEWIC 2009), a provincial recovery plan (British Columbia Ministry of Environment 2015) and a federal recovery strategy (ECCC 2020) have been prepared, and Critical Habitat across the species’ Canadian distribution has been partially identified; a schedule of studies outlining activities required to complete Critical Habitat identification has been proposed. Surveys have been conducted across the species’ range to identify undocumented sites and to improve knowledge of the area of occupancy at known sites. A significant discovery was the detection of a population in the Pemberton Valley in 2011, representing an occurrence disjunct from coastal sites and the first confirmed record from mainland British Columbia. Intensive long-term monitoring at a Vancouver Island site (Observatory Hill) has provided new information on abundance, habitat use, and movements of the snakes. Stewardship efforts have been undertaken on private lands to engage landowners to search for and monitor Sharp-tailed Snakes and to protect and improve habitat. A recent and rapid expansion of an invasive predator, Common Wall Lizard, poses a potentially significant threat to Vancouver Island and Gulf Island subpopulations.

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2021)

Wildlife species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special concern (SC)
(Note: Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.)

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at risk (NAR)
(Note: Formerly described as “Not In Any Category”, or “No Designation Required.”)

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data deficient (DD)
(Note: Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” [insufficient scientific information on which to base a designation] prior to 1994. Definition of the [DD] category revised in 2006.)

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Current classification

Class: Reptilia
Order: Serpentes
Family: Dipsadidae (formerly Colubridae)
Genus: Contia
Species: C. tenuis (Baird and Girard, 1952)

Two species of Contia are currently recognized with the identification of C. longicauda in parts of California and Oregon as a separate species (Feldman and Hoyer 2010). The taxonomy of the Canadian populations remains unchanged.

English: Sharp-tailed Snake, Common Sharp-tailed Snake
French: Couleuvre à queue pointue
Indigenous common names: unknown

Morphological description

Sharp-tailed Snake is a small, slender snake with adults 205–455 mm in total length (Matsuda et al. 2006). Individuals from British Columbia (BC) are usually shorter than 340 mm. Body scales are smooth and unkeeled, and there is a thorn-like scale at the tip of the tail, from which the species derives its common name (see cover image). The anal plate is divided. The back and sides are red- or yellow-brown with no obvious stripes in adult snakes, occasionally greyish, and the ventral surface is banded with black and white. Detailed descriptions and illustrations can be found in Storm and Leonard (1995), Leonard and Ovaska (1998), and Matsuda et al. (2006).

Population spatial structure and variability

The distribution of Sharp-tailed Snake in the northern portion of the species’ global range is highly fragmented (Cook 1960; Stebbins 1966; Storm and Leonard 1995; Figure 1). Factors leading to this fragmentation are poorly understood but might be associated with climate cooling that occurred after the Hypsithermal Interval, which ended about 5,500 years ago. A fragmented northern distribution is characteristic of a southward contracting range (Green et al. 1996).

The Canadian distribution is patchy within a matrix of developed areas and unsuitable habitat. Subpopulations on the Gulf Islands are isolated from each other and from Vancouver Island subpopulations by stretches of ocean. The sole known mainland British Columbia site in Pemberton Valley is isolated from the coastal sites by ocean (Strait of Georgia) and over 200 km of mostly unsuitable terrestrial habitat. The nearest mainland site is in Washington State ~300 km south of Pemberton.

Feldman and Spicer (2002) examined genetic variation of the then nominal species C. tenuis from California and southern Oregon using mitochondrial DNA markers. They found two distinct major clades, which were subsequently identified as separate species: Contia longicauda (Forest Sharp-tailed Snake) in northern coastal California and parts of southern Oregon and C. tenuis in the interior of California, most of Oregon, Washington, and British Columbia (Feldman and Hoyer 2010; Figure 1). The sole DNA sample from British Columbia, from North Pender Island, was very similar to specimens from Washington, northern Oregon, and interior and southern California, corresponding to the range of the larger clade (C. Feldman pers. comm. cited in COSEWIC 2009). Finer scale genetic differentiation across the species’ Canadian distribution has not been examined.

Designatable units

Sharp-tailed Snake was previously assessed as a single designatable unit (DU; COSEWIC 1999, 2009). Since the last assessment, an isolated population in the Pemberton Valley on mainland British Columbia has been documented (Anthony 2013), constituting a second DU, the Coast Mountains DU. The Vancouver Island and Gulf Islands subpopulations form the Pacific Coast DU. The Pacific Coast DU extends into Washington State, including the San Juan Islands and adjacent coastal mainland subpopulations there (if they still exist), but no gene flow across the international border is possible at present due to oceanic barriers. The relict Coast Mountains DU stands alone, isolated from all other populations.

According to COSEWIC guidelines, populations must be both discrete and evolutionarily significant to be considered as DUs (Appendix F5 of COSEWIC O and P manual, November 2020). Evidence for discreteness (D1, D2) and significance (S1, S2) is discussed below.

Discreteness

D1. Evidence of heritable traits or markers that clearly distinguish the putative DU from other DUs (e.g., evidence from genetic markers or heritable morphology, behaviour, life history, phenology, migration routes, vocal dialects, etc.), indicating limited transmission of this heritable information with other DUs.

Not applicable. Genetic analyses have not been conducted, and heritable features of morphology or life history features between the two putative DUs have not been investigated. In particular, data are lacking for the Pemberton Valley population.

D2. Natural (i.e., not the product of human disturbance) geographic disjunction between putative DUs such that transmission of information (e.g., individuals, seeds, gametes) between these “range portions” has been severely limited for an extended time and is not likely in the foreseeable future. “Extended time” is intended to mean that sufficient time has passed that either natural selection or genetic drift are likely to have produced discrete units, given the specific biology of the taxon.

The island (Vancouver Island and Gulf Islands) and mainland (Pemberton Valley) populations are geographically isolated from each other by >200 km., which include impassable open ocean and mountainous terrain. Along with other coastal reptiles and amphibians inhabiting the Pacific faunal province (O’Connor and Green 2016), Sharp-tailed Snakes probably extended their range into British Columbia along the Pacific dispersal route from a refuge in the south after the retreat of Pleistocene glaciations ~11,000 years BP, reaching their maximum distribution during the warmer Hypsithermal period 8,000–5,500 years BP. Approximately 5,000 years BP, rising sea level would have isolated the island populations and left the relict Pemberton Valley population stranded. This scenario assumes that subsequent dispersal over land or ocean is highly improbable; this is supported by the habitat specialization, extremely limited movements, and apparently poor dispersal ability of the snakes (see Movements, Migration, and Dispersal).

Evolutionary significance

S1. Direct evidence or strong inference that the putative DU has been on an independent evolutionary trajectory for an evolutionarily significant period, usually intraspecific phylogenetic divergence indicating origins in separate Pleistocene refugia.

Although both putative DUs originated from the same glacial refugium, they have likely been on different evolutionary trajectories for thousands of years (see D2 above).

S2. Direct evidence or strong inference that can be used to infer that the putative DU possesses adaptive, heritable traits, that cannot be practically reconstituted if lost. For example, persistence of the discrete, putative DU in an ecological setting where a selective regime is likely to have given rise to DU-wide local adaptations that could not be reconstituted. See Practical Considerations/Best Practices.

Adaptive differences in life history traits, such as growth, maturation, and reproduction, are plausible due to climatic differences among the two regions. Habitat-specific local adaptations have been reported for other snakes, including differential growth rates of neonate Western Terrestrial Gartersnakes (Thamnophis elegans) during the first year of life in common garden experiments (Bronikowski 2000). The long separation time between the two putative DUs has provided ample time for such local adaptations.

Both populations occur in the Pacific Amphibians and Reptiles faunal province, but their habitats are very different. On Vancouver Island and the Gulf Islands, the species occurs in the Coastal Douglas-fir (Pseudotsuga menziesii) (CDF) biogeoclimatic zone, which encompasses a narrow strip of land on the southeast coast of Vancouver Island and adjacent Gulf Islands and includes a fringe of the mainland coast (Meidinger and Pojar 1991; FLNROD 2019). In Pemberton Valley, the species occurs within the interface of the Coastal Western Hemlock (Tsuga heterophylla) (CWH) and the Interior Douglas-fir (IDF) biogeoclimatic zones. So far, despite extensive searching, Sharp-tailed Snake has been found only in open-canopy Douglas-fir forest on the IDF side (Anthony unpubl. data 2019).

The coastal and mainland populations occur in different forest types and experience different climatic regimes, as reflected in the biogeoclimatic zone designations. The coastal snakes inhabit Garry Oak (Quercus garryana) - Arbutus (Arbutus menziesii) - Douglas-fir woodlands (ECCC 2020), whereas the mainland snakes inhabit mainly coniferous, Douglas-fir forests and their fringes; Garry Oak and Arbutus are absent (Anthony unpubl. data). The coastal sites experience mild winters with little or no snow accumulation and short periods of sub-freezing temperatures, resulting in a long, moist spring activity period for snakes, lasting for several months (Köppen climate classification Csb - Mediterranean warm/cool summer climates). Conversely, the mainland population experiences longer, harsher winters with significant snow and a relatively short spring period (Köppen climate classification Dsb - warm summer continental or hemiboreal climate). The difference between the warmest and coolest month (average monthly temperature) during a year is greater in Pemberton (23.5 °C) than along the coast (11.3 °C in Saanich, Vancouver Island; 13.6 °C in Ganges, Saltspring Island; Appendix 1).

Given a) the small size of the Pemberton (Coast Mountains) population, b) its position at the northern limit of the species’ range (~500 km north of nearest mainland population in Washington) with considerable difference in climate regimes between Coast Mountains and Pacific Coast populations, and c) the very long isolation time of the Pemberton population (~5000 years minimum), a strong inference of an independent evolutionary trajectory of this population is reasonable.

Special significance

Habitats of Sharp-tailed Snake (Pacific Coast population) include sensitive Arbutus - Douglas-fir and Garry Oak ecosystems, where it co-occurs with many rare plants and invertebrates. Disjunct populations at the northern extremity of the species’ global distribution in Canada may contain unique, yet undocumented genes and adaptations (Hardie and Hutchings 2010).

Sharp-tailed Snake is one of only two species in the genus Contia, not closely related to any other genera. It provides material for study of systematics and evolution. This species has no known economic or cultural significance.

Distribution

Global range

The geographic range of Sharp-tailed Snake extends from southwestern British Columbia to the southern Sierra Nevada and to the central coast of California (Figure 1). The species is relatively widespread and locally abundant in Oregon and California (Cook 1960; Hoyer et al. 2006), but records from Washington and British Columbia are restricted to a few, isolated areas (Leonard and Ovaska 1998; ECCC 2020). The nearest occurrences in Washington State are from San Juan and Orcas islands, adjacent to the southern Gulf Islands of British Columbia (O’Donnell and McCutchen 2008; Rensel et al. 2019).

Canadian range

In Canada, Sharp-tailed Snake is known from southern Vancouver Island, from southern Gulf Islands in the Strait of Georgia (North and South Pender, joined by a bridge, Saltspring, and Galiano), and from a small, restricted area of the Pemberton Valley in mainland British Columbia (Figure 2). An additional record from the southern interior of British Columbia (McGillivray Lake near Chase; Tanner 1967) is most likely erroneous and is not considered further in this report. The Canadian range represents less than 5% of the species’ global distribution.

The Pacific Coast DU is known from 15 subpopulations (excluding the Chase record), seven on Vancouver Island, eight on southern Gulf Islands; the Coast Mountains DU is known from one subpopulation only, Pemberton Valley (Table 1). All except the Galiano Island subpopulation are considered extant (i.e., have records within the past 20 years). Subpopulations in both DUs were defined by distribution of records within 5 km distance of each other, unless separated by insurmountable barriers (Hammerson 2004 in NatureServe 2019). Since the previous COSEWIC (2009) assessment, five new subpopulations have been documented in the Pacific Coast DU: three on Vancouver Island (Langford, Mount MacDonald; Sooke, Mount Peden; Cowichan Valley), two on Saltspring Island (Mount Tuam; Reginald Hill); additionally, a new population (DU) with one subpopulation has been documented on the British Columbia mainland (Pemberton). The new discoveries reflect increased search effort, rather than range expansion.

^* Subpopulation number corresponds to that used in the provincial recovery plan (British Columbia Ministry of Environment 2015) except for subpopulations 17 and 18, which are based on new (2016 and 2021, respectively) occurrences.
^** The status of Sharp-tailed Snake subpopulations is as follows: Extant – population has been verified recently (<20 years); Historical – recent information verifying the continued existence of the population is lacking (i.e., records are >20 years).
^{^} Metchosin, Mary Hill – Galloping Goose and Sooke Road subpopulations identified in the recovery strategy (ECCC 2020) were joined by a record from near Matheson Lake in the intervening area.

In the Pacific Coast DU, the record from near Ladysmith, Cowichan Valley, is the northernmost record from Vancouver Island and the only one outside of the Capital Regional District (Figure 2). Two subpopulations identified in the recovery strategy (ECCC 2020), Metchosin, Mary Hill – Galloping Goose and Sooke Road, were joined by a record from near Matheson Lake in the intervening area. Additionally, new sites within known subpopulations have been found on North and South Pender islands, Saltspring Island, and in the Highlands district in Greater Victoria. With the documentation of a new site ~500 m from the sole previous (1949) observation, the status of the Mount Washington Road subpopulation on North Pender Island has changed from historical (as in ECCC 2020) to extant. Also, the status of Saltspring Island, Northeast, subpopulation has changed from unknown (ECCC 2020) to extant with several confirmed records from private properties and a roadkill in the Long Harbour area. Previously undocumented sites are shown in Figure 3.

Documentation of the Coast Mountains DU in Pemberton Valley is the first confirmed occurrence from mainland British Columbia. Of significance is the isolation of the population from its coastal counterparts. All 13 Sharp-tailed Snake sites are along a restricted span (< 5 km) of the west- and south-facing Mackenzie Ridge on the north side of Pemberton Valley. As a uniquely east-west trending feature in otherwise north-south trending mountains, the valley has a high heat-retention capacity. This characteristic, along with highly fertile lacustrine and fluvial deposits, has made Pemberton a centre for diverse agriculture. The same microclimatic characteristics also support the most diverse reptile fauna on the south coast of British Columbia; a unique assemblage of five reptiles (Sharp-tailed Snake; Valley Gartersnake, Thamnophis sirtalis fitchi; Terrestrial Gartersnake, T. elegans; Northern Rubber Boa, Charina bottae; Northern Alligator Lizard, Elgaria coerulea) is found here and nowhere else in the province or country. Most of the surrounding area is mountainous and too high in elevation to be expected to support Sharp-tailed Snakes.

Extent of occurrence and area of occupancy

Extent of occurrence (EOO) was calculated using the minimum convex polygon method around occurrence records since 2000 (approximately three generations) and clipped to the Canadian jurisdiction. Index of area of occupancy (IAO) was calculated by the area covered by 2x2 km grid cells containing occurrence records. For the Pacific Coast population, EOO was calculated as 1,839 km², including ocean, and IAO as 112 km² (28 2x2 km grid cells) (Appendix 2). For the Coast Mountains population, EOO was calculated as 1.11 km² and IAO as 12 km² (three 2x2 km grid cells) (Appendix 2); however, because EOO cannot be smaller than IAO, it was adjusted to 12 km². If the two putative DUs are considered together, EOO is 4,556 km² (including ocean) and IAO 124 km² (30 2x2 km grid cells).

In the previous status report (COSEWIC 2009), when only the Pacific Coast population was known, EOO was given as 995 km² (including ocean) and IAO as 96 km² using all records. The new values for the Pacific Coast DU represent an increase of 84.8% in EOO and 16.7% in IAO as a result of increased search effort over the past decade.

Search effort

From the rediscovery of Sharp-tailed Snake in British Columbia in 1948 on North Pender Island to the early 1990s, encounters with the species were largely serendipitous (Spalding 1995). A concerted effort to locate the species at known and new sites began in 1996. From 1996 to 1999, all previously reported localities and their vicinity on Vancouver, Pender, Saltspring, and Galiano islands were surveyed; likely habitats on Mayne and Saturna Islands and many smaller islands in the Strait of Georgia were also surveyed (Engelstoft and Ovaska 1999). From 2002 to 2008 surveys were carried out in habitats deemed suitable on 14 federal properties on Vancouver Island and the southern Gulf Islands, including six properties on Department of National Defence (DND) lands, one on National Research Council lands, five within the Gulf Islands National Park Reserve on North Pender, South Pender, Prevost, and Saturna Islands, and two on Canadian Coast Guard lands. Some survey effort took place on Galiano Island, site of the sole record of the species in 1981, but the island has not been surveyed with the same intensity as other large southern Gulf Islands.

Surveys since the previous status report (COSEWIC 2009) are outlined in Appendix 3. They include continuing surveys of potentially suitable habitat and monitoring of known sites on Vancouver Island and the Gulf Islands. Sites surveyed included federal lands managed by the Department of National Defence and National Research Council, Capital Regional District Parks, British Columbia Provincial Parks and Ecological Reserves (Mount Tuam and Mount Maxwell), and private residential lands as part of stewardship projects. Significant largely unsurveyed potential habitat exists within occupied IAO grid cells and surrounding areas in Sooke (Mount Peden) and Metchosin (Mount McDonald) on Vancouver Island, and Reginald Hill and Mount Maxwell on Saltspring Island.

On mainland British Columbia, annual surveys have been carried out in the Pemberton area since the discovery of the species there in 2011. Targeted surveys for this species in the valley and adjacent areas up to 10 km distant (Owl Ridge and Birkenhead River Valley, Rutherford Creek, Lillooet Lake eastern shore) were conducted annually from 2011 to 2019. The first site was found by Anthony while searching for Rubber Boa. Subsequent search effort focused on areas with similar exposures that resembled what was understood to be Critical Habitat in the coastal part of the species’ range in British Columbia. Google Earth’s sun tracker function was used to generate a polygon map of early-spring warm spots in the Pemberton Valley. Because these polygons fortuitously encompassed all previously discovered sites, further searching was concentrated mostly within the polygon areas. Due to private land access issues, a further criterion was added in recent years to search only Crown Lands within these polygons. Approximately 50 sites were surveyed, and seven new occurrences were found, all in the Pemberton Valley (Anthony unpubl. data 2019). The greatest effort took place in 2014 on provincial Crown lands.

Habitat

Habitat requirements

In British Columbia, Sharp-tailed Snake occurs in woodland habitats, where it is found predominantly in and around small rocky openings on hillsides with a warm exposure (British Columbia Ministry of Environment 2015). A mosaic structure of habitats with ample thermoregulation opportunities might be particularly important at the northern limits of its distribution, where the species may occur near its physiological limits. The habitat must contain suitable sites for hibernation, egg-laying, and foraging in a configuration available for individual snakes that typically confine their seasonal movements to relatively small areas (tens to hundreds of metres; see Movements, Dispersal, and Migration).

On Vancouver Island and the Gulf Islands, all records are from the CDF biogeoclimatic zone, which covers about 2000 km², most of which is below 150 m asl (MacKinnon and Eng 1995). Sharp-tailed Snake occurs in Douglas-fir-Arbutus woodlands and in Garry Oak-dominated hillsides (British Columbia Ministry of Environment 2015). In the Pemberton area, the records are from the interface between CWH and IDF biogeoclimatic zones at altitudes from 200 m (valley bottom) to 400 m asl. All records are from within or at the immediate edge of open-canopy Douglas-fir forest (Anthony unpubl. data 2019). Garry Oak savannah is lacking, and there is also no Arbutus. Common understorey shrubs include Oregon-Grape [Mahonia (Berberis) spp.], Saskatoon (Amelanchier alnifolia), Oceanspray (Holodiscus discolor), and Indian Plum (Oemleria cerasiformis). These are all plants that the CDF and IDF zones share, especially in warm aspect sites.

Hibernation and aestivation sites

Sharp-tailed Snakes hibernate in underground refugia, at microsites that remain frost-free and contain sufficient moisture to prevent dehydration, similar to other snakes in northern climates (Gregory and Campbell 1987). On Observatory Hill, three hibernation sites have been located in rocky southwest-facing forest openings based on seasonal movements of tagged snakes to and from these sites (Engelstoft et al. 2019a and unpubl. data 2019b). Individual snakes showed fidelity to these sites, returning to them repeatedly across years. Other presumed hibernation sites were located in similar habitats at this and other coastal sites (Engelstoft and Ovaska 1999; Engelstoft et al. 2019a). In Pemberton, a large artificial talus (layers of rock) slope created by a blasting operation ~15 years ago, provided hibernation sites for Sharp-tailed Snakes and other reptiles (Anthony unpubl. data 2019). When the site (since developed) was discovered in 2012, it was in early stages of succession, with a ground cover of grasses, small shrubs, and Oregon Grape. The snakes were found ≤50 m from the forest edge. Aestivation probably also occurs underground, but there is no information on specific sites.

Egg-laying sites

There are no records of egg-laying sites from British Columbia and only one record from the USA (Oregon: Brodie et al. 1969). Hatchling-sized snakes have been found in fall and early spring presumably close to egg-laying sites in talus on south- and southwest-facing openings on Saltspring Island (Engelstoft and Ovaska 1997, 1999), on Vancouver Island (Observatory Hill, Engelstoft et al. unpubl. data 2019b), and in Pemberton (Anthony unpubl. data 2019). On Saltspring Island, hatchlings have been found under artificial cover-objects on woody debris away from talus (Matthias pers. comm. 2020), suggesting that talus is not necessarily required. In Pemberton, hibernation and egg-laying sites seemed to be in close proximity to one another, as a preponderance of hatchlings were found in fall and spring in the same place as emerging adult and subadult snakes in spring. In Oregon, Brodie et al. (1969) found an egg-laying aggregation of five species of reptiles, including Sharp-tailed Snake, within a 14 m² patch of talus. The habitat consisted of an unshaded, grass-covered southern slope by an oak knoll. Brodie et al. (1969) suggested that suitable warm slopes with talus were in short supply causing snakes to aggregate at communal egg-laying sites.

Microhabitats and importance of cover

Sharp-tailed Snakes are semi-fossorial and use existing crevices and cracks in the soil or bedrock, or burrow into loose substrates. When on the surface, the snakes are seldom found out in the open and away from cover, such as provided by rocks or coarse woody debris. Comparison of habitat at observation points and random points 50 m away revealed that microsites where the species was found on Vancouver Island and the southern Gulf Islands had a southern exposure, shallow soil and leaf litter, and a large cover of rock (Wilkinson et al. 2007). Similarly, on Observatory Hill, captures of snakes under artificial cover-objects were associated with rock cover, especially pebbles (Engelstoft et al. 2017). During extensive monitoring on Mount Tuam, Saltspring Island, Sharp-tailed Snakes were detected mainly under artificial cover-objects on woody debris substrate (L. Matthias pers. comm. 2020). A complex, three-dimensional substrate structure is characteristic of most occupied sites.

The recovery strategy for the species, which has partially identified Critical Habitat, described the biophysical attributes of Critical Habitat (ECCC 2020, pp. 7–8) as follows:

• “sparsely forested or treeless rocky openings (~10 m diameter and greater) with warm (southerly) aspects; which
  • provide for thermoregulation (warming)
• within 20 m of the openings, open canopy forest habitat (20-60% closure; following Wilkinson et al. 2007), which
  • supports prey populations (e.g., slugs), and
  • provides thermoregulation (cooling); and
• within these openings and the adjacent open canopy forest, 3-dimensional features composed of rock (e.g., talus slopes or patches, or fissures in rock outcrops) or coarse woody debris (including large decaying logs or stumps with sloughing bark) that provide microhabitats which
  • provide temperature regimes for thermoregulation (warming and cooling)
  • retain moisture to support inactive phases and prey species for foraging
  • provide locations for egg-laying and adequate moisture and temperature regimes for incubation, and
  • provide cover/shelter during active and inactive phases”

Habitat trends

Vancouver Island and Gulf Islands

Woodland habitats occupied by Sharp-tailed Snake are naturally fragmented, compounded by human habitation, roads, and other developments (CRD Regional Map 2019). With its fertile soils and mild maritime climate, the CDF biogeoclimatic zone in the rain shadow of the Vancouver Island and Olympic mountains has long attracted settlers, and the area is currently home to about 75% of British Columbia’s human population (Islands Trust 2019). It is the most disturbed biogeoclimatic zone in the province with almost half of its land base converted to agricultural, urban, or other uses (Coastal Douglas-fir Conservation Partnership 2019). The area continues to be under pressure from urban sprawl and development. Road densities, reflecting habitat fragmentation, are among the highest in British Columbia on southeastern Vancouver Island; only 19% of the land base is over 500 m from a road (i.e., paved or unpaved road or trail with authorized motor vehicle access; Environmental Reporting BC 2019).

Within the CDF zone, Sharp-tailed Snake occurs in Arbutus- and Garry Oak-associated ecosystems, many of which are rare and listed at risk (BC CDC 2019). About 10% of the original (pre-European settlement) area of Garry Oak ecosystems remains, and only about half of them are relatively intact (Lea 2006). The remaining 5% are highly impacted and/or severely degraded by invasive alien species or other factors.

All Sharp-tailed Snake records from the islands, apart from the Cowichan Valley record, are from the Capital Regional District (CRD), which covers the extreme southern portion of Vancouver Island and the southern Gulf Islands. From 2011 to 2018, human population within the district grew by 12.4%, ranging from a modest 4.1% in rural Metchosin to 29.3% in the fast-growing municipality of Langford (Environmental Reporting BC 2019). Coverage by impervious surfaces, reflecting permanent habitat loss, has increased by 80% from 1986 to 2011 within CRD municipalities on Vancouver Island (calculated from Table E6 in Caslys 2013). Human population growth and associated rates of land conversions will most likely continue throughout the region over the next decades.

While not directly indicating trends, existing land use can be useful to depict past habitat loss and to assess the scope of some threats. Land use within each occupied IAO grid cell was assessed by visually examining the presence and/or approximate percentage coverage by habitat alteration type and other habitat characteristics from GoogleEarth™ satellite map (Table 2); road length/IAO cell was calculated using GIS. For the Pacific Coast DU, 77% of 26 grid cells (one cell that was >95% ocean was excluded) had low- or high-density housing developments (10–80% coverage/cell); 30.8% had a coverage of development in excess of 50%/cell. Road density rated as moderate (1–6 km of road/4 km² cell) or high (>6 km of road/4 km² cell) occurred in 46.2% of the grid cells, and the same percentage of cells was intersected by major roads. A smaller percentage of cells (23.1%) contained agricultural areas (10–40% coverage/cell). Areas considered protected from development included parks and ecological reserves, conservation covenants, and federal lands (managed by the Department of National Defence, National Research Council Canada, Parks Canada, Transport Canada); these occurred in 53.9% of the grid cells, with the highest proportion on Vancouver Island. Search effort has largely focused on these areas due to management imperatives and access, introducing a potential bias.

^*1 grid cell that was >95% water was excluded
^{^}Includes areas cleared for development

Total no. of grids

Vancouver Island = 14
Saltspring = 8
North and South Pender* = 4
Pacific Coast DU (total # of grids)= 26
Pacific Coast DU (total; % of grids)= na
Coast Mountains DU: Pemberton= 3

Pemberton

In general, the IDF biogeoclimatic zone is less developed than the CDF zone with less permanent habitat alteration and low road densities. However, Pemberton Valley, a driving distance of 153 km from Vancouver, is becoming increasingly desirable for both recreation and residence as the human population in the Lower Mainland continues to expand and nearby Whistler becomes unaffordable. The human population in the Squamish-Lillooet Regional District has grown by over 85% since 1986, and the village of Pemberton by 13% from the 2011 to 2018 census (Environmental Reporting BC 2019). Most of the valley bottom is farmed and within designated Agricultural Land Reserve (B.C. Ministry of Agriculture 2009). Since 2016, residential development has accelerated, expanding onto the surrounding hillsides and into Sharp-tailed Snake habitat, with two of the first sites discovered now non-existent (see Threats).

For the Coast Mountains DU, all three grid cells had either low- or high-density housing developments (10–15% coverage/grid cell) (Table 2). All three cells also contained agricultural areas (15–50% coverage/grid cell). Road density was deemed moderate in one and low (<1 km/cell) in two cells, and barriers (highway and large river) were present in all three cells. A golf course covered an additional ~10% of one cell and an industrial site ~15% in another cell. No areas protected from development were identified.

Biology

Biology of Sharp-tailed Snake remains poorly known, reflecting difficulties in studying this elusive and semi-fossorial snake. In British Columbia, most existing data on the life history and general biology of the species are derived from multi-year studies that used artificial cover-objects to locate snakes at Vancouver Island sites (mainly Cole Hill, Mary Hill, Observatory Hill), North Pender Island (Magic Lake), and Saltspring Island (Vesuvius, Mount Tuam) (Isaac and Gregory 2003; Engelstoft and Ovaska 2009, 2010; Matthias 2009; Engelstoft et al. 2019a). Work on life history at four of these sites (Cole Hill, Mary Hill, Magic Lake, Vesuvius) from 1997 to 2005 was summarized by Govindarajulu et al. (2011). The Observatory Hill site has been studied annually from 2010 to 2020 (Engelstoft et al. 2017, 2019a, 2020). British Columbia sources are augmented by studies from the United States of America (USA), where the species is more common.

Life cycle and reproduction

Sharp-tailed Snake is oviparous with a clutch size of 3–5 eggs, based on information from the USA (Storm and Leonard 1995). In Oregon, Brodie et al. (1969) discovered a communal egg-laying site used by five species of reptiles, including 43 Sharp-tailed Snake eggs in groups of two, three, four, eight and nine eggs; the larger groups might have resulted from communal oviposition by two or more females. In British Columbia, the mean number of eggs detected through palpation of 16 gravid females was 3.1+  1.1 (Govindarajulu et al. 2011), but no egg clutches have been found. Whether individual females reproduce annually or less frequently is unknown.

Body size of 85–323 mm snout-vent length (SVL) was recorded from Vancouver Island and the Gulf Islands (Govindarajulu et al 2011: n = 88, mean: 209–236 mm at 4 sites; Engelstoft et al. unpubl. data 2019b: n = 151, mean = 178 mm, median = 188 mm; Observatory Hill). The total length of individuals from Pemberton ranged from 95 to 340 mm (Anthony unpubl. data 2019); when adjusted to SVL by subtracting tail (mean of 16% of total length), the values are comparable to those from the coast (n = 34; median = 210 mm; range = 80–286 mm). Hatchling-sized juveniles have been found in fall and early spring both on the islands (Govindarajulu et al. 2011; Engelstoft et al. unpubl. data 2019b) and in Pemberton (Anthony unpubl. data 2019). Little growth probably takes place over winter for young that hatch in fall, which is presumed the norm. At coastal sites, juveniles initially grew rapidly at an average rate of 19.0 mm SVL/year (± 10.1 mm SD), but growth slowed down with increasing body size (Govindarajulu et al 2011). The average body size of gravid females was 260 mm SVL (± 22.5 mm SD), and the smallest was 219 mm. Annual growth rates of adults averaged 4.1 mm (± 5.1 mm SD) for males and 4.6 mm (± 6.7 mm SD) for females (Govindarajulu et al 2011).

Time to sexual maturity was estimated at 5–6 years for a population on North Pender Island, as extrapolated from growth rates (Govindarajulu et al. 2011). However, high uncertainty is associated with this value due to a very small number of juveniles in the sample. A value of 2–3 years is more realistic, similar to age at first reproduction for Sharp-tailed Snakes in Oregon (Hoyer pers. comm. 2020) and other small snakes, including Ring-necked Snake (Diadophis punctatus), Dekay’s Brownsnake (Storeria dekayi), Redbelly Snake (S. occipitomaculata), and Smooth Greensnake (Opheodrys vernalis) (Semlitsch and Moran 1984; CHS 2019). Lifespan is unknown but is at least eight to nine years based on recapture histories of individuals first caught as adults and recaptured five to six years later at the North Pender and Observatory Hill study sites (Govindarajulu et al. 2011; Engelstoft et al. 2019a, unpubl. data 2019b). Annual survivorship was estimated using Program Mark (White and Burnham 1999) for North Pender as 0.73 and 0.74 for adult females and males, respectively (site sampled from 1997 to 2004; Govindarajulu et al. 2011), and for Observatory Hill as 0.53 for both sexes combined (site sampled from 2011 to 2018; Engelstoft et al. 2020).

Generation time (GT) can be roughly estimated as GT=AM+1/AMR; where AM = age at maturity and AMR = annual adult mortality rate. Thus, GT= 5–7 years (rounded to the nearest year), based on annual survival rate of 0.53–0.73 and age at maturity of 3 years.

Physiology

Sharp-tailed Snake appears to be associated with cool, moist micro-sites (Cook 1960). Stebbins (1954) found individuals active and with food in the stomach at cloacal temperatures as low as 11–16°C (52–61F). In coastal British Columbia, the species has been found in all months of the year, but most frequently in spring (March–early June) and fall (September–October) (Engelstoft et al. unpubl. data 2019b). In Pemberton Valley, most records are from end of April to May and from October (Anthony unpubl. data 2019). Sharp-tailed Snakes are inactive during cold periods in winter and warm, dry periods in summer, but there is no information on their physiology during these times. On Observatory Hill (2011–2019), ambient temperatures during surveys when Sharp-tailed Snake was found ranged from 7°C to 29°C, while temperatures under occupied roofing asphalt cover-objects ranged from 7°C to as high as 46°C.

In the laboratory, three snakes provided with a thermal gradient ranging from 10°C to 45°C for 24 h selected relatively low temperatures (20–22°C) (Isaac and Gregory 2003). In the same study, crawling speed of snakes maintained at three different temperatures (16, 22 and 26°C) were similar, suggesting that the snakes were able to perform across a wide range of relatively low body temperatures.

Movements, dispersal, and migration

Movement patterns of Sharp-tailed Snakes are poorly known and difficult to study due to the snakes’ secretive habits, small body size and slender shape that preclude the use of radio-telemetry. Most detailed movement data are from PIT (Passive Integrated Transponder) tag telemetry on Observatory Hill (Engelstoft et al. 2019a). From 2011 to 2019, 46 individuals (31 adult males and 15 adult females) were tagged with PIT tags surgically inserted into the body cavity. After release, snakes were located with a portable scanner that allowed their detection up to ~20–30 cm, including below ground. The mean home range size (Minimum Convex Polygon method) was 179.6 m² ± 81.4 m² (n = 22 snakes) and the mean distance between two farthest detections 37.3 m ± 7.4 m (cumulative straight-line distance; n = 29 snakes). Four individuals undertook movements over 100 m with the greatest documented movement of 139 m; this snake was monitored over four years (2014–2018).

PIT tag telemetry data from Observatory Hill support previous information, obtained at this and other sites on Vancouver Island and the Gulf Islands from artificial cover object surveys, that individual snakes are relatively sedentary and do not undertake long seasonal migrations. For example, within a rural residential area on North Pender Island, 16 recaptured adult snakes were found within areas of usually less than 55 m along the greatest dimension (mean = 25 m; range: 16–93 m) over a year (Engelstoft and Ovaska 1999). The longest movement was by an adult male that moved a straight-line distance of 93 m within a 3-week period in March–April (Engelstoft and Ovaska 1999). In relatively undisturbed habitat on Vancouver Island (Cole Hill), five recaptured snakes moved straight-line distances of up to 32 m within one active season (Ovaska and Engelstoft 2005).

Sharp-tailed Snakes have occasionally been found on roads, one individual was crushed in the doorway of a building, and another was found in the basement of another building (Engelstoft et al. unpubl. data 2019b). Whether these individuals were dispersing or moving to or from hibernation or aestivation sites is unknown.

Interspecific Interactions

Diet

The diet of Sharp-tailed Snake is thought to consist largely of small slugs (review in Cook 1960; Leonard and Ovaska 1998). Zweifel (1954) interpreted the elongated teeth of the species as an adaptation for feeding on their slippery prey. Cook (1960) pointed out that since the European colonization of western North America and nearly ubiquitous presence of introduced slugs, both the structure and distribution of the prey base of Sharp-tailed Snake have changed drastically. The snakes may have benefited from the abundance of introduced slugs. In coastal British Columbia, various species of both introduced and native slugs are common in habitats occupied by the species, including native species (taildroppers, Prophysaon spp.) and introduced species (Arion and Deroceras spp.) (Ovaska and Engelstoft 2005; Ovaska et al. 2014–2019). Prey availability likely restricts foraging to wet, cool periods or habitats and hence potentially affects both distribution and seasonal and daily activity patterns of the snakes.

Predators

A variety of vertebrate predators may prey on Sharp-tailed Snakes, but few cases of predation have been documented. The species has been recovered from the stomachs of Brook Trout (Salvelinus fontinalis) and Western Toad (Bufo, now Anaxyrus, boreas; cited in Leonard and Ovaska 1998); an American Robin (Turdus migratorius) was noted carrying a juvenile Sharp-tailed Snake on Saltspring Island (landowner report to Matthias pers. comm. 2019). Likely predators in British Columbia include various birds that scratch the ground such as corvids (Corvidae), as well as Raccoon (Procyon lotor) and shrews (Sorex spp.). Scarring and missing tail tips of Sharp-tailed Snake, suggesting injuries from unsuccessful predation attempts, have been documented both from island sites (Engelstoft and Ovaska 1999) and from Pemberton (Anthony unpubl. data 2019). Secretive habits of Sharp-tailed Snakes, including their tendency to remain hidden under cover objects, provide some protection from visual predators. The introduced invasive Common Wall Lizard, which is presently expanding dramatically on Vancouver and the Gulf islands, may prey on eggs and hatchling snakes and has the potential to eliminate or greatly reduce some subpopulations in the near future (see Threats, Coast population DU).

Adaptability

Sharp-tailed Snakes can coexist with humans within residential areas, provided that sufficient cover and other required habitat features are present. In California and Oregon, many observations are from backyards and other disturbed areas within or near urban areas (Cook 1960; Hoyer et al. 2006). In British Columbia, numerous records on the Gulf Islands are from rural residential areas, where the snakes have been found occasionally in compost heaps, orchards, borders of gardens, and woodpiles. They readily use artificial cover-objects of wood, metal, or asphalt roofing for refuge (Engelstoft and Ovaska 2000). However, snakes within populated areas are vulnerable to habitat fragmentation, road mortality, pesticides, predation by Domestic Cats (Felis catus) and subsidized predators such as Raccoons, and loss of key habitat features (see Threats).

Limiting factors

Low reproductive potential and slow ability to recover from perturbations contribute to the vulnerability of the species. Oviparous reproduction probably limits the northward distribution of all egg-laying reptiles, which, in contrast to viviparous species, must rely entirely on conditions at the oviposition site to provide a suitable thermal environment for the developing embryos (Gregory and Campbell 1987). The availability of nest sites with appropriate thermal conditions is an important factor determining the distribution of oviparous species (Shine 2004).

Habitat fragmentation and availability of suitable oviposition sites are probably important factors limiting the distribution and population growth of Sharp-tailed Snake in British Columbia. Small patches of specialized habitat may limit population size and reduce genetic variability, hence increasing vulnerability of subpopulations to stochastic effects and habitat modification, as reported for other species of snakes (e.g., Guicking et al. 2004). On a local scale, warm, partially exposed slopes with stable talus or other cover that forms suitable breeding habitat for the species might be in short supply. Low reproductive potential, including small clutch size, and relatively sedentary habits probably limit the ability of the species to rebound after perturbations.

Population sizes and trends

Sampling effort and methods

Population monitoring has been carried out on lands managed by the Department of National Defence, National Research Council, and Capital Regional District Parks on Vancouver Island and on private residential properties on North Pender and Saltspring islands as part of research and stewardship projects. On numerous residential properties, landowners were engaged in monitoring efforts with varying levels of intensity. Snakes were located using artificial cover-objects, usually made of asphalt/fiberglass roofing material and arranged in various patterns. At most monitored sites, attempts have been made to determine the area of occupancy.

Intensive monitoring from three sites provides information on patterns of abundance: rural residential property on North Pender Island, sampled in 1996–2000 and sporadically in 2001–2004 (Govindarajulu et al. 2011) and two Vancouver Island sites, Heals Rifle Range, sampled intensively in 2005–2008 (Engelstoft and Ovaska 2009), and Observatory Hill, sampled intensively in 2011–2019 (Engelstoft et al. 2019a). Individual snakes were identified from pattern mapping (dark mottling under the snout and chin); PIT-tagging was used as an auxiliary method on larger individuals on Observatory Hill (see Movements, Dispersal, and Migration). The Observatory Hill study provides the most accurate data due to its long duration, regular surveys of a standardized set-up of artificial cover-objects, and a relatively large number of Sharp-tailed Snakes detected over the course of the study (151 individuals). Demographic parameters from data for this and the North Pender Island site were estimated using Program Mark (White and Burnham 1999).

Abundance

At Observatory Hill, the subpopulation of Sharp-tailed Snakes that used 162 artificial cover-object stations dispersed in suitable habitat was estimated to consist of a mean of 127.7 snakes (SE = 56.2, 95% CL 56.0–291.3) in 2011 (first year of monitoring) and 80 snakes (SE = 28, 95% CL: 40–157) in 2018 (last year of monitoring). The cover-objects were assumed to collectively sample 21.03 ha of habitat, based on 39.1 m radius circular area around each station (polygons for stations closer than this distance from each other were merged); this radius represented the 90^th percentile of movement distances by individual snakes derived from PIT-tag telemetry at the site (Engelstoft et al. 2019a). Adjusted for the proportion of adults in the sample (0.83), density estimates ranged from a mean of 4.98/ha (95% CL: 2.18–11.36) in 2011 to 3.12/ha (95% CL: 1.56–6.12) in 2018. Rough mean densities were calculated for Heals Rifle Range by simply dividing the number of individuals by the area sampled and comparing the value with that from Observatory Hill calculated the same way. The values for the two sites were similar (Heals: 6.9/ha based on 31 adults detected over 4 years with cover-objects estimated to sample 4.5 ha; Observatory Hill: 6.9/ha based on 151 adults detected over 8 years within 21.3 ha). The Heals data are based on uneven spatial and temporal sampling effort, and data were not analyzed statistically. A much higher density than at either of the above sites was recorded for a small (~1 ha) study site spanning two adjacent rural residential properties on North Pender Island, where the population was estimated to consist of 49 individuals (95% CL: 43–65); all observations were within an area of 733 m², resulting in a density estimate of 0.067 snakes/m² within the occupied patch (Govindarajulu et al. 2011). Because of the small area sampled and extremely patchy distribution of the snakes, this density cannot be extrapolated to larger areas at landscape scale.

Assuming that the densities at Observatory Hill in 2018 are representative of current average abundance across the species’ Canadian range, a rough estimate of population size can be calculated by extrapolation to the area occupied by subpopulations (Table 3). The Pacific Coast population was estimated to consist of a mean of 11,782 adults (95% CI= 5,891-23,110) and the Coast Mountains population of 345 adults (95% CI= 172-676). These values may represent minimum estimates because (a) area of occupancy is incompletely known at most sites and is based on known occurrences, and (b) subpopulation size could not be estimated for three coastal sites with only one or two records (Mount Peden, Mount McDonald, and Reginald Hill) that contain relatively large areas of unsurveyed potentially suitable habitat.

^ Metchosin, Mary Hill – Galloping Goose and Sooke Road subpopulations identified in the recovery strategy (ECCC 2020) were joined by a record from near Matheson Lake in the intervening area.

Vancouver Island and Gulf Islands totals:

Area of occupancy (MCP, ha) = 3776.2
Population estimate (mean d=3.12) = 11782
Population estimate (Lower CL d=1.56) = 5891
Population estimate (Upper CL d=6.12) = 23110

All areas grand totals:

Area of occupancy (MCP, ha) = 3886.7
Population estimate (mean d=3.12) = 12127
Population estimate (Lower CL d=1.56) = 6063
Population estimate (Upper CL d=6.12) = 23787

Fluctuations and trends

Historical trend

The population has undoubtedly experienced declines in the past due to habitat loss, fragmentation, and alteration associated with land conversions to urban and agricultural developments (see Habitat Trends). However, no quantitative estimates of declines are available (see Table 2 for land use within IAO grid cells).

Past 3-generation trend

Population trends across Sharp-tailed Snake’s Canadian distribution have likely declined at an unknown rate due to continuing habitat loss. No inferences of population trends can be made from trends in EOO or IAO because most sites were only recently documented. Sharp-tailed Snake has been detected at all historical sites visited within the past two decades, with the exception of Galiano Island, indicating continuing presence.

At two monitored sites within the Pacific Coast DU, populations were possibly declining, as determined from monitoring data over the past 1 to 2 generation periods: North Pender, nonsignificant decline of 11%/year (Govindarajulu et al. 2011); Observatory Hill, nonsignificant decline of 7%/year (Ovaska et al. 2018). Due to difficulties in locating these elusive snakes, even intensive sampling efforts would result in very low ability to detect declines. A modelling exercise based on the Observatory Hill dataset found that a significant decline of 50%/year could be detected with 80% power and alpha 0.05 within approximately 4 years, 30%/year decline in 5.5 years, and 10% decline/year in 9.5 years of intensive sampling conducted multiple times each year (Challenger and Robichaud 2018 in Ovaska et al. 2018).

The Coast Mountains Population was described only recently, and little trend information is available. A decline is inferred from habitat loss associated with the development of a subdivision in occupied habitat soon after the species discovery there in 2011 (see Threats and Limiting Factors).

Future trends

A continuing decline is projected and suspected for both DUs based on threats from multiple sources (see Threats). Habitat quality and quantity are projected to decline as a result of human activities and developments.

Population fluctuations

Annual fluctuations in population size have been documented for Observatory Hill (Challenger and Robichaud 2018 in Ovaska et al. 2018). However, extreme fluctuations, i.e., over an order of magnitude, are undocumented and highly unlikely given the life history characteristics of the species (low reproductive potential, longevity).

Population fragmentation

Sharp-tailed Snake habitat is patchily distributed in the landscape, and this fragmentation has been exacerbated by human activities in developed areas, particularly on the coast (CRD Regional Map 2019). The population is undoubtedly fragmented to some degree because there are insurmountable barriers to movements posed by busy roads, paved areas, and high-density developments. Compared to snakes that undergo seasonal migrations, such as Western Rattlesnake (Crotalus viridis) and Great Basin Gophersnake (Pituophis catenifer deserticola), Sharp-tailed Snake is relatively sedentary with movements in the order of hundreds of metres or less, compared to several kilometres in larger snake species (see Movements, Dispersal, and Migration). Therefore, movements of Sharp-tailed Snake among habitat patches occupied by subpopulations are severely curtailed.

The population was previously deemed severely fragmented (COSEWIC 2009); however, current interpretation of severe fragmentation, more in line with IUCN criteria (i.e., over 50% of the population is in habitat fragments smaller than required to support viable subpopulations), is uncertain. Although small subpopulations within urbanized landscapes may be in peril, the largest subpopulation (Highlands - Saanich) within the Pacific Coast DU is in relatively continuous habitat that is mostly protected from development (i.e., is within parks or managed federal lands). New sites have been discovered within the past decade within the Sea to Sea Regional Park Reserve (Mount Peden, Mount McDonald) where substantial continuous, protected habitat also exists. However, subpopulations within these larger habitat patches are not necessarily secure. The introduced, invasive Common Wall Lizard (Podarcis muralis) has been documented from the Highlands – Saanich site, and there are scattered records from East Sooke, near the Sea to Sea Regional Park Reserve. Given its rapid spread on Vancouver Island, it could potentially affect the long-term viability of the larger subpopulations of Sharp-tailed Snake. Adverse impacts on the snakes through predation of eggs or hatchlings is a strong but as yet undocumented possibility (see Threats: Threat 8. Invasive and other problematic species). Because population level impacts on the snakes are undocumented and uncertain, severe fragmentation of the Pacific Coast DU cannot be confirmed but remains a credible possibility.

Only one subpopulation is known from mainland British Columbia, precluding the application of the severe fragmentation concept to the Coast Mountains DU.

Rescue effect

Rescue of the Pacific Coast Population from the United States is impossible because of oceanic barriers. The nearest population in the United States is on Orcas Island in the San Juan archipelago, ~30 km from South Pender Island and Vancouver Island. Rescue of the Pemberton Valley population is also impossible due to the great separation distance between the nearest population in Washington State (~300 km) in relation to the movement capabilities of the snakes (10s or, at most, 100s of m). Furthermore, roads, agricultural areas, and high-density urban developments in the Lower Fraser Valley would pose insurmountable barriers to cross-border movements of snakes.

Threats

The IUCN Threats Calculator was applied to Sharp-tailed Snake to the two putative DUs by a panel of experts (Appendices 4 and 5). The process consists of assessing impacts for each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10-year period), severity (predicted population decline within the scope within the next 10 years or 3 generations, whichever is longer; i.e., 15 years for Sharp-tailed Snakes), and timing of each threat. The overall threat impact is calculated considering the separate impacts of all threat categories and can be adjusted by the panel.

Threats are discussed below in their perceived order of importance for each DU.

Pacific Coast Population (DU1)

The overall threat impact was rated as High (Appendix 4). The greatest threat is deemed to be from Residential and Commercial Development, followed by Invasive and other problematic species. Other, lower impact threats are from Transportation and service corridors, Human intrusion and disturbance, Natural system modifications, and Climate change and severe weather. Impacts from Pollution are unknown.

Threat 1. Residential and commercial development (threat impact “medium”)

Description of threat

This threat accrues mainly from housing and residential development, and associated habitat loss and fragmentation. Loss of habitat features that support important life history functions (foraging, thermoregulation, overwintering/hibernation, summer inactivity, refuge, oviposition, and seasonal movements and dispersal) is of particular concern. Loss of connectivity within and between subpopulations is also an issue. Sharp-tailed Snakes have specific habitat requirements within localized areas, and because of their limited dispersal capabilities, they are not readily able to avoid habitat disturbance by moving to other areas.

Scope

Sharp-tailed Snake occurs within relatively densely populated areas of BC, where urban development continues to expand. Occurrences outside of areas protected from development, such as in parks and federal lands, are at risk. In addition to known sites, suitable potential habitat where the species might occur but is yet to be detected occurs within areas under development pressure.

The following subpopulations are exposed to this threat:

• Metchosin, Mary Hill – Galloping Goose – Sooke Road: Federal lands on Mary Hill (~178 ha) are currently protected from development but face an uncertain future, as a large portion of the property is released by the Department of National Defence. Transfer to Scia’new First Nation is in progress (as of June 2020). The area contains designated Critical Habitat. Residential development may take place to a limited extent elsewhere within this subpopulation range
• Langford, Mill Hill: Part of the hill is within Mill Hill Regional Park, but urban development is encroaching onto the hill. Since the previous assessment, a new housing development resulted in the loss of 11.4 ha of habitat, representing 44.4% of the natural habitat on the hill
• Saltspring Island, Northwest: A new subdivision was cleared for development in Sharp-tailed Snake habitat in 2005 (Channel Ridge) but is yet to be completed. Development may continue in other areas, but no specific plans are known
• North Pender, Magic Lake: Some infilling and new housing are possible amidst existing rural subdivision
• South Pender Island: Some new housing is possible within rural landscape

In addition to the above, small-scale developments, such as replacement of older houses and subdivision of larger lots, are possible within all subpopulation areas on private lands. The scope was assessed as “restricted” (11–30% of the population affected), reflecting potential developments within five subpopulation areas.

Severity

Severity of the impact is dependent on the scale and nature of the development, ranging from elimination of a subpopulation within high-density developments to coexistence, presumably at reduced snake densities, within low-density developments where key habitat features are retained. If the area affected is large or developed intensively, connectivity within and between subpopulations would be lost, leading to isolation and increased extinction risk from perturbations. On average, where it occurs, the severity of this threat was assessed as serious (31–70% decline) due to habitat loss.

Threat 8. Invasive and other problematic species (threat impact “medium-low”)

Description of threat

Predation by subsidized natural predators, such as Raccoons, corvids, and American Robins, and by house cats could be a significant source of mortality in human modified landscapes. California Quail (Callipepla californica), a historical introduction to British Columbia, is a potential predator of juvenile Sharp-tailed Snakes. Cats are predators in urbanized areas, and there is one old record of cat predation from a residential property on North Pender, and two records from a site on Saltspring Island.

Introduced Common Wall Lizard is rapidly expanding its range on southern Vancouver Island and the Gulf Islands (Bertram 2004; Engelstoft et al. 2020) and has been documented in increasing numbers at two Sharp-tailed Snake study sites in the districts of Highlands and Saanich (Engelstoft and Ovaska 2008; Engelstoft et al. 2019a, unpubl. data 2019b). Its rapid spread from a few roadside sightings in 2011 to cover the entire hillside where Sharp-tailed Snakes occur by 2019 was documented at the Observatory Hill site (Engelstoft and Ovaska unpubl. data 2019b). It is now present in six of 15 Sharp-tailed Snake subpopulations, which collectively account for ~85% (>10,000 of ~11,800) of estimated mature snakes in the Pacific Coast population, and is encroaching on seven additional subpopulations (Table 4).

Subpopulation total (historical site included, as the species may still exist there) = 11,782 (5891-23110) Pop estimate (mature snakes)

Because Common Wall Lizard can reach extremely high densities (up to 6000 individuals/ha) in Europe (Barbault and Mou 1986) and similar or higher densities on Vancouver Island according to anecdotal information (Engelstoft et al. 2020), impacts on Sharp-tailed Snake, primarily from predation of eggs and hatchlings, are of grave concern. Within its natural range in Europe, Common Wall Lizard is an opportunistic forager, feeding on a wide range of prey (Barbault and Mou 1986). It is primarily insectivorous but can also take small vertebrate prey; cannibalism has also been documented (Žagar and Carretero 2012). There is an anecdotal report from Vancouver in 2015 of “a green lizard with a smooth back that had a neonate garter snake in its jaws”, presumed to be a European Wall Lizard (Engelstoft et al. 2020). Competition for egg-laying sites could also occur but is less likely to be important than predation due to communal egg-laying habits of many reptiles, including a documented case involving Sharp-tailed Snake (Brodie et al. 1969). Population-level effects of Common Wall Lizard on Sharp-tailed Snake are unstudied and uncertain, but potentially destabilizing.

Introduced slugs occur throughout much of the species’ range. By increasing prey availability, they may be beneficial to the snakes, countering some of the negative impacts.

Scope

The scope was assessed as “large” (31–70% of the population affected) based on the prevalence of introduced predators and subsidized natural predators within the species’ range.

Severity

The severity was assessed as moderate to slight (1–30% population decline). The impacts are expected to be negative and may be considerable, but they have not been studied. Vulnerability to cat predation may be less than that for more abundant garter snakes that bask in the open. Semi-fossorial habits and the propensity of Sharp-tailed Snake to occur under cover-objects may also protect it from predation from litter-foraging birds but not from introduced Common Wall Lizard.

Threat 4. Transportation and service corridors (threat impact “low”)

Description of threat

This threat accrues from road mortality when snakes are moving within or among habitat patches. The snakes may be attracted to edge habitats and gravel banks on roadsides, increasing mortality risk. New roads in occupied habitat pose additional risks during the construction phase and from further fragmentation of habitats.

Scope

Roads intersect or abut snake habitat at most known sites, but larger areas of habitat away from roads exist in some areas, including Mount McDonald and Mount Peden on Vancouver Island and Reginald Hill on Saltspring Island. On Saltspring Island, the snakes occur in the immediate vicinity of a busy ferry terminal. On Vancouver Island, highway expansion is in progress through potential Sharp-tailed Snake habitat in Langford. The scope was assessed as “large” (31–70% of the population affected). Although 77% of IAO grid cells contained moderate or high road density (Table 2), individuals in the middle of habitat patches even at sites adjacent to roads would not be expected to encounter them due to their limited movements.

Severity

Several cases of road mortality are known from Pender and Saltspring islands (Spalding 1995; Matthias unpubl. data 2019; specimens at RBCM). Mitigating factors include site fidelity, semi-fossorial habits, and lack of extensive seasonal movements such as undertaken by larger snakes. However, any additional mortality might be detrimental to small populations (Row et al. 2007). The severity was assessed as slight (1–10% population decline) given these considerations.

Threat 6. Human intrusion and disturbance (threat impact “low”)

Description of threat

This threat accrues from recreational activities and from work and other activities. Recreational activities and other human use of sensitive habitats can destroy important microhabitat features, such as talus and coarse woody debris, and cause damage to the ground vegetation and moss layer. On the other hand, hiking and activities confined to trails are expected to have minimal impact. Gardening and landscaping activities, which include removal of rocks, can destroy remnant natural habitat patches and remove cover needed for refuges; they can also increase the risk of accidental mortality from digging or use of power tools. This threat category also includes foot traffic and soil disturbance associated with invasive plant removal, which is ongoing at several sites (e.g., Observatory Hill). The threat from military activities was considered negligible due to cessation of operational use of most of Mary Hill for training and occurrence of the species away from the shooting range at Heals Rifle Range.

Scope

Much of the habitat is located either in parks or on private residential lands. Due to their proximity to populated areas, many regional parks, in particular, are heavily used and include a network of authorized and unauthorized trails. Off-trail activities, such as mountain biking and motorbiking activities, have been documented from some Sharp-tailed Snake sites, including occupied sites in Highlands and Saanich and at multiple sites on Saltspring Island. The scope was assessed as “large” (31–70% of the population affected).

Severity

While inadvertent destruction of talus patches during recreational activities can be serious, the frequency of such events within the large scope of the threat is probably relatively low. Similar considerations apply to mortality and habitat destruction from gardening and landscaping activities. The severity was assessed as slight (1–10% population decline), based on the average impact of the combined activities included in this category.

Threat 7. Natural system modifications (threat impact “low”)

Description of threat

Habitat modification by introduced, invasive plants, such as Scotch Broom (Cytisus scoparius), is prevalent throughout much of the Sharp-tailed Snake’s range, including hillsides occupied by the species; monocultures of Scotch broom create shade, which is most likely harmful. Spurge-laurel (Daphne laureola) is also invading some sites but is often more prevalent in moister, more densely wooded sites than in Sharp-tailed Snake habitats. Many other introduced or invasive plants, such as Foxglove (Digitalis purpurea) occur or are spreading in Sharp-tailed Snake habitats, but their effects on the species are unknown.

Garry Oak habitats on hillsides inhabited by the Sharp-tailed Snake are historically fire-maintained. Fire prevention policies have allowed fuel to accumulate, and high human use of many of these habitats has increased the risk of fires. Conifer encroachment on small openings and open canopy woodlands decreases habitat quality and has been noted on Observatory Hill, Mount Tuam, and other sites. The effects will become more important beyond the next 10-year period.

Scope

The scope was assessed as “pervasive to large” (31–100% of the population affected) because of the prevalence of invasive shrubs in Sharp-tailed Snake habitats.

Severity

The severity was assessed as slight (1–10% population decline). The impacts are expected to be negative, but they have not been studied.

Threat 11. Climate change and severe weather (threat impact “low”)

Description of threat

Adverse effects are expected mainly from increased frequency and severity of summer droughts, which are expected to restrict surface activity and foraging opportunities. While the snakes may shift their seasonal activity periods in response to milder, wetter winters and drier summers predicted under climate change models, prolonged summer droughts could reduce survivorship. Over the long term, the species may benefit from the expansion of open woodland associated with climate change, provided that dispersal to new areas is possible in landscapes fragmented by human activities.

Scope

The scope was assessed as “pervasive” (71–100% of the population affected) because of the relatively small Canadian range of the Pacific Coast population, all of which would experience similar climatic conditions.

Severity

The severity was assessed as slight (1–10% population decline). The impacts are expected to be negative and will increase over the long-term beyond the next 10-year period.

Threat 9. Pollution (threat impact “unknown”)

Possible control programs against introduced mollusc pests of agricultural products could threaten Sharp-tailed Snakes. Aggressive pesticide use could harm snakes that feed on contaminated prey, but there are no data.

Coast Mountains Population (DU2)

The overall threat impact was rated as High (Appendix 5). The greatest threat is deemed to be from Residential and commercial development, followed by Human intrusion and disturbance. Other, lower impact threats are from Energy production and mining, Transportation and service corridors, Natural system modifications, Invasive and other problematic species, and Climate change and severe weather. Impacts from Pollution are unknown (see Pacific Coast Population above for explanation).

Threat 1. Residential and commercial development (threat impact “high”)

Description of threat – See Pacific Coast DU.

Scope

Beginning in 2016, a subdivision was developed in known Sharp-tailed Snake habitat. Expansion of the development to adjacent areas on the ridge is ongoing, and is expected to increase within the next 10 years. The first phases of the development are complete, but subsequent phases are in progress or planned and consist of high-density housing, mostly below 400 m in elevation where Sharp-tailed Snakes occur. As of January 2021, habitat at three of 14 known Sharp-tailed Snake sites had been destroyed by the development, which is ongoing (Anthony pers. obs.). Other non-contiguous hillside developments are underway in Pemberton, with no information on the potential of Sharp-tailed Snake occupation of these areas. The scope was assessed as “large” (31–70% of the population affected).

Severity

An apparent elimination of the species was observed as a result of a subdivision development. In spring 2012, Sharp-tailed Snake was discovered on a hillside adjacent to an artificial talus slope created years before during blasting for a housing development that was subsequently halted due to regulatory infractions. The talus was used as an overwintering site as adults were found here in spring 2013, 2014, 2015, and 2016. Smaller talus beside it was apparently used for egg-laying as hatchlings were present in fall and spring. Another sub-adult individual was found on the same hillside 0.5 km below this site, close to the valley bottom. In 2016, however, the housing development was re-started, and by 2017 both sites on the hillside had disappeared due to clearing, blasting, and road-building that also removed important habitat from a large surrounding area.

Construction practices, such as blasting and use of heavy machinery, cause widespread destruction of habitat, and the development footprint is large. The severity was assessed as “serious” (31–70% population decline) because the type of development (residential subdivisions) affects relatively large areas and has a high potential to destroy important habitat features, such as hibernation and egg-laying sites.

Threat 6. Human intrusion and disturbance (threat impact “medium”)

See Pacific Coast DU for description of the threat.

Scope

A network of mountain bike and motorized vehicle trails covers the entire range of this population. Unauthorized new bike trails, including climbing trails with long ridgebacks, are ubiquitous and traverse through delineated Critical Habitat, where there is no signage or other on-the-ground protection. There is increased pressure for recreational use from people in new housing developments, surrounding areas, and Lower Mainland. Use of the area may have increased because of COVID-19. The scope was assessed as “pervasive” (71–100% of the population affected).

Severity

The severity was scored as moderate (11–30% population decline), which is higher than for Pacific DU because of increased exposure to high recreational use in prime habitat.

Threat 3. Energy production and mining (threat impact “low”)

Description of threat

This threat accrues from mining and quarrying. Gravel or rock extraction for road construction or other purposes is harmful for the snakes by potentially causing direct mortality and destroying important habitat for refuges. Effects are particularly harmful if talus patches where snakes congregate for hibernation or egg-laying are destroyed.

Scope

Gravel extraction for road construction and flagstone quarries is possible in snake habitat but restricted to small areas. Illegal gravel extraction has been documented in the area in the recent past. An active quarry exists near the occupied sites. While past quarrying activities may have created habitat, reactivation of these sites would cause mortality or displacement of snakes using the sites, and hence they are included. The scope was assessed as “small” (1–10% of the population affected).

Severity

Considering the potential of quarrying to destroy essential habitat features where snakes may congregate, the severity was assessed as “extreme” (71–100% of decline).

Threat 4. Transportation and service corridors (threat impact “low”)

See Pacific Coast DU for description of the threat.

Scope

The scope includes existing road network of mainly secondary roads and logging and other access roads, including those servicing new and prospective residential developments. New access roads associated with subdivision have greatly increased road traffic including recreational users across the hillside; for example, mountain bike parking lots may have 300–500 trucks/weekend. The scope was assessed as “restricted” (11–30% of the population affected). Both road density and traffic volumes are expected to increase with expanding housing developments on the hillsides.

Severity

The severity was scored as moderate (11–30% population decline), which is higher than for Pacific DU because of increased exposure to high traffic volumes through prime habitat and small size of the population; loss of only a few snakes may have population-level effects.

Threat 7. Natural system modifications (threat impact “low”)

See Pacific Coast DU for description of the threat and factors affecting severity.

Scope

Much of the occupied habitat is invaded by Scotch Broom, and as clearings and road building continue, the plant is likely to spread. Himalayan Blackberry (Rubus armeniacus) is also invading some areas. The scope was assessed as “pervasive to large” (31–100% of the population affected).

Threat 11. Climate change and severe weather (threat impact “low”)

Description of threat

The threat accrues from increased summer droughts as described for Pacific Coast DU and from storms and flooding. The hillsides occupied by Sharp-tailed Snakes are prone to erosion from flooding events, resulting in loss and damage of microhabitats. Storms associated with flooding events occur annually and may increase with climate change in both severity and frequency.

Scope

The scope was assessed as “pervasive” (71–100% of the population affected) based on threat from droughts, because the same climatic and weather patterns affect the entire small area occupied by the population.

Severity

The severity was assessed as slight (1–10% population decline) within the pervasive scope, but moderate (11–30% population decline) within areas affected by storms and flooding events. The impacts are expected to be negative and will increase over the long-term beyond the next 10-year period.

Number of threat-based locations

Pacific Coast Population (DU1)

The greatest plausible threats to the population over the next 10 years are from predation by rapidly expanding invasive European Wall Lizard populations, and conversion of habitat to housing and urban areas. Although there is uncertainty about the timing and severity of the Wall Lizard impact, its rapid spread will likely impact large areas simultaneously on Vancouver Island and separately on the three Gulf Islands. Credible estimates of number of locations based on the Wall Lizard threat and accounting for time lags, range from 7 to 11. These include three on Gulf Islands (Salt Spring, North Pender, South Pender) and 4 to 8 on Vancouver Island, with uncertainty about expected decline rates (hence doubling number of locations for two generations or 10 years). Habitat conversion is likely to take place at multiple sites mainly within areas of six subpopulations (see Threats). The actual number of such events is unknown, but considering each development as a separate event would result in many more than ten locations.

Alternatively, land ownership could be used as an indicator of a threat-location due to similarity in management of threats from invasive species and recreational activities. The number would also be much greater than ten, given that the species occurs on numerous private land parcels, in addition to federal, provincial, and municipal lands under different management regimes.

All occurrences are under the same climatic regime, and summer droughts were identified as a threat. However, there is much uncertainty about the impacts, and although adverse effects are plausible, there are no data. Therefore, considering climate change and severe weather as a basis for identifying locations is premature for this population.

Coast Mountains Population (DU2)

The greatest plausible threat to the population over the next 10 years is from conversion of habitat to housing and urban areas. The private land parcel where the development is projected to occur over the next 10 years could be considered from one to three locations, depending on how the different phases of the development are counted. The remainder of the range could be considered one location, if ongoing heavy recreational activity is considered a single threatening event, resulting in a total of 2 to 4 locations. Superimposed on the above are storms and flooding events, which are predicted to affect 11–30% of the range over the next 10 years.

Protection, status and ranks

Legal protection and status

Sharp-tailed Snake is listed as Endangered under the federal Species at Risk Act and is in Schedule 1, the official list of species at risk in Canada. A federal recovery strategy has been prepared (ECCC 2020). It identifies Critical Habitat as a description of known biophysical attributes of the habitat that are required to support life-cycle processes (functions). The strategy also provides a list of examples of activities likely to result in the destruction of Critical Habitat and a schedule of studies outlining the activities required to complete its identification. Geospatial areas containing Critical Habitat for Sharp-tailed Snake total 552.68 ha, distributed across the species’ Canadian distribution. The Species at Risk Act requires protection of important habitats, including designated Critical Habitat and residences for threatened and endangered species on federal lands, and provides provisions for their protection on other lands through the safety net clause. British Columbia’s Wildlife Act prohibits the collection, handling, and trade of all native wildlife species without a permit. Where the species occurs within national parks, its habitats are protected from development by the Canada National Parks Act. British Columbia Parks Act does not directly address protection of species at risk and their habitats, which may be covered by individual park management plans (Govindarajulu pers. comm. 2020).

Non-legal status and ranks

NatureServe (2019) provides the following status designations for Contia tenuis: Global status: G5 – Secure (last reviewed 2 February 2016); National status: USA – N5 (Secure); Canada – N1N2 (Critically Imperilled/Imperilled); sub-national status: California – S5 (Secure); Oregon – S4 (Apparently Secure); Washington – S3 (Vulnerable); British Columbia – S1S2 (Critically Imperilled/Imperilled). COSEWIC assessed the species as Endangered in 1999, and the status was reconfirmed in 2008. The species is on the Red List of species at risk in British Columbia.

Habitat protection and ownership

On Vancouver Island, many occurrences are from parks or lands that are currently protected from development. Federal lands with occurrence records include Observatory Hill, managed by National Research Council and home of Dominion Astrophysical Observatory, and Mary Hill and Heals Rifle Range, managed by the Department of National Defence; a part of Mary Hill is currently in the process of being transferred to the Scia’new First Nation. The species occurs in several localities within the CRD regional parks and trails system (Mount Work, Mill Hill, Lone Tree Hill, Sea to Sea reserve, Galloping Goose trail right-of-way), and in smaller municipal parks. On the Gulf Islands, the species occurs mostly on private lands, but it is also present in protected areas. These include Gulf Islands National Park Reserve (Greenburn Lake on South Pender Island), and Mount Tuam, managed by Transport Canada, CRD regional park (Reginald Hill) and a small municipal park on Saltspring Island.

In Pemberton Valley, the species occurs on private, municipal, and provincial crown lands, most of which are unprotected. The Ském’em (formerly Fulton) Wetlands that is on public land, managed by the Squamish Lillooet Regional District/Village of Pemberton/Stewardship Pemberton, is the only area within the population’s range that is currently protected from development; however, threat from intensive recreational use is present.

Acknowledgements

This report is an update from previous status reports (COSEWIC 1999, 2009), prepared by Kristiina Ovaska and Christian Engelstoft. Unless otherwise noted, distribution maps were prepared by Sydney Allen, COSEWIC Secretariat. The report writers thank the numerous people who generously shared data, reports, or provided contacts. Special thanks to Laura Matthias for providing unpublished data and responding to numerous queries.

Authorities contacted

Canadian Wildlife Service
Eric Gross
Rhonda Millikin
Randal Lake

Department of National Defence
Rachel McDonald

Natural Resources Canada
Andrea Schiller

Parks Canada
Pippa Shepherd
Pippi Lawn
Shelley Pruss
Brian Reader
Tara Sharma

Canadian Museum of Nature
Robert Anderson

Royal British Columbia Museum
Gavin Hanke

British Columbia provincial representatives
Gregory A. Wilson
Purnima Govindarajulu

British Columbia Conservation Data Centre
Lea Gelling
Katrina Stipeck

COSEWIC Non-government Science Members
David F. Fraser
Arne Mooers

COSEWIC Secretariat
Sonia Schnobb
Rosana Soares
Jenny Wu
Sydney Allen

Recovery team
Eric Gross

Other relevant contacts
Michael Dunn (Mayne Island Conservancy)
Keith Erickson (Galiano Island Conservancy Association)
Michelle Evelyn (independent biologist)
Jared Hobbs (J Hobbs Ecological Consulting Ltd.)
Laura Matthias (independent biologist)
Aimee Mitchell (Athene Ecological)
Kathryn Luttin (Salt Spring Island Conservancy)

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Biographical summary of report writer(s)

Kristiina Ovaska has an MSc degree from Acadia University and PhD degree in biology from the University of Victoria. Her academic experience includes two post-doctoral studies on population biology and ecology of amphibians (McGill University; University of British Columbia). Presently, she is research associate at Royal British Columbia Museum (Victoria, British Columbia) and partner in Biolinx Environmental Research Ltd. (Sidney, British Columbia). Kristiina is the author of more than 40 publications in the refereed scientific literature, as well as numerous technical reports, largely on species at risk. She is Co-chair of COSEWIC Amphibians and Reptiles Specialist Subcommittee (SSC). Together with Christian Engelstoft, she has worked on inventory and research projects on Sharp-tailed Snake since 1996 and has been a member of the Sharp-tailed Snake Recovery Team since its inception in 2011.

Christian Engelstoft has an MSc degree in Biology from the University of Victoria. He has worked as a consultant in British Columbia since 1995, including extensive studies on Sharp-tailed Snake and other species at risk. Christian and Kristiina are presently partners in Biolinx Environmental Research Ltd. and have collaborated on numerous projects on Sharp-tailed Snake and other species since 1996.

Leslie Anthony has a PhD degree in Zoology from the University of Toronto and was an NSERC post-doctoral fellow at the Redpath Museum, McGill University. He has published some 20 scientific papers on a range of topics in evolution, ecology, and toxicology. Leslie discovered the only known mainland population of Sharp-tailed Snake in Canada in Pemberton in 2011. Since then, he has continued annual surveys in the area, expanding our knowledge of the distribution and habitat requirements of the species.

Collections examined

No collections were examined. Royal British Columbia Museum, BC Conservation Centre, and iNaturalist were queried for records. Additional records were obtained from Habitat Acquisition Trust (Victoria, British Columbia). Salt Spring Island Conservancy, and personal files by C. Engelstoft and L. Matthias.

Appendices

Appendix 1. Differences in monthly temperatures (A) and precipitation (B) between ranges of Pacific Coast (DU1) and Coast Mountains (DU2) populations of Sharp-tailed Snakes. Data for DU1 are average values for Saanichton, Vancouver Island, and Ganges, Saltspring Island; data for DU2 are for Pemberton. Pemberton is warmer in summer and colder in winter, and receives more precipitation (except in spring) than the islands. Data from Climate Data (2019).

Appendix 2. Extent of occurrence (EOO) and index of area of occupancy (IAO) maps for Pacific Coast population (top) and Coast Mountains (Pemberton) population (bottom) of Sharp-tailed Snake. Maps prepared by Sydney Allen (COSEWIC Secretariat)

Appendix 3. Summary of search effort for Sharp-tailed Snake in British Columbia since the previous COSEWIC (2009) status report, 2009–2019

^* TCS – time-constrained survey of natural cover; ACO – artificial cover-object survey with repeated checks each year; OPP - Opportunistic

Appendix 4. Threats calculator results for Sharp-tailed Snake, Pacific Coast population

Threats assessment worksheet

Species or ecosystem scientific name:

Sharp-tailed Snake, Contia tenuis, Pacific Coast population

Element ID:

Not applicable

Elcode:

Not applicable

Date:

2020-06-02

Assessor(s):

Dave Fraser (Facilitator/COSEWIC Member), Kristiina Ovaska (A&R Co-chair/SRW), Tom Herman (A&R Co-chair), Rosana Soares (Secretariat), Christian Engelstoft (SRW), Leslie Anthony (SRW), Nicholas Cairns (A&R SSC member), Lea Randall (A&R SSC member), Pamela Rutherford (A&R SSC member), Sara Ashpole (A&R SSC member), Morgan Davies (PCA), Eric Gross (CWS- Recovery), Laura Mathias, Andrea Schiller (NRCan)

Reference(s):

COSEWIC status report, draft January 2020

Assigned overall threat impact:

B = High

Impact adjustment reasons:

Not applicable

Overall threat comments:

Generation time 5-7 years; IAO: 108 km²; Population estimate (mean): 11,782 adults; 14 subpopulations; Scores in red for Threat 8: for 8.1, scope and severity were changed from Large-Restricted and Unknown as per 2 June call to Large and Moderate-Slight respectively after further review of Wall Lizard threat in particular, including discussion at the November 2021 Species Assessment Meeting. For 8.2, severity was changed from Unknown to Slight to match revisions to DU2.

Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).

Appendix 5. Threats calculator results for Sharp-tailed Snake, Coast Mountains population.

Threats assessment worksheet

Species or ecosystem scientific name:

Sharp-tailed Snake. Contia tenuis, Coast Mountains population

Element ID:

2020-06-02

Elcode:

Not applicable

Date:

Not applicable

Assessor(s):

Dave Fraser (Facilitator/COSEWIC Member), Kristiina Ovaska (A&R Co-chair/SRW), Tom Herman (A&R Co-chair), Rosana Soares (Secretariat), Christian Engelstoft (SRW), Leslie Anthony (SRW), Nicholas Cairns (A&R SSC member), Lea Randall (A&R SSC member), Pamela Rutherford (A&R SSC member), Sara Ashpole (A&R SSC member), Morgan Davies (PCA), Eric Gross (CWS- Recovery), Laura Mathias, Andrea Schiller (NRCan)

References:

COSEWIC status report, draft January 2020

Assigned overall threat impact:

B = High

Impact adjustment reasons:

Not applicable

Overall threat comments:

Generation time 5-7 years; IAO: 12 km²; Population estimate (mean): 345 adults; 1 subpopulation; Scores in red - changed as a result of 10 June 2020 discussion with Pemberton people (Veronica Woodruff and Les Anthony), C. Engelstoft, and K. Ovaska.

Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).