Magnum Mantleslug (Magnipelta mycophaga): COSEWIC status appraisal summary 2022

Official title: COSEWIC status appraisal summary on the Magnum Mantleslug (Magnipelta mycophaga) in Canada

Special Concern

2022

COSEWIC assessment summary

Assessment summary – December 2022

Common name: Magnipelta mycophaga

Scientific name: Magnipelta mycophaga

Status: Special Concern

Reason for designation: The large slug species, up to 80 mm in length, is endemic to the northern Columbia Basin in western North America. Half of the global range is in southeastern British Columbia. The species occurs in patchy habitat and is confined to moist, cool microsites within coniferous forests at mid-to high elevations. Despite extensive searches, there are only 22 subpopulations recorded within its Canadian range. Fragmentation of its habitat continues to be a threat, as are logging and habitat shifts, droughts, storms, and flooding. It may become Threatened if threats are neither reversed nor managed with demonstrable effectiveness and is currently close to meeting Threatened criteria.

Occurrence: British Columbia

Status history: Designated Special Concern in May 2012. Status re-examined and confirmed in December 2022.

COSEWIC status appraisal summary

Magnum Mantleslug

Limace à grand manteau

Magnipelta mycophaga

Range of occurrence in Canada (province/territory/ocean): British Columbia

Wildlife species

SAS 6 Change in eligibility, taxonomy or designatable units: no

Explanation:

No changes since the previous assessment.

Range

SAS 7 Change in Extent of Occurrence (EOO): Yes

SAS 8 Change in Index of Area of Occupancy (IAO): Yes

SAS 9 Change in number of known or inferred current locations^{Footnote 1}: Yes

SAS 10 Significant new survey information: Yes

Explanation:

Distribution records for the species exist from 22 occurrences, representing 16 subpopulations (that is, those >1 km apart or 3 km apart in continuous habitat) at scattered localities across the species’ Canadian range (BCECCS 2018; Figure 1). Since the previous COSEWIC (2012) status report, which included records from 1992 to 2010, the species has been detected on 9 occasions; the last record is from 2015 (see Table 1 in BCECCS 2018 for a list of localities). In addition, a specimen collected in 1936 on Mount Revelstoke (a previously known locality) has come to light. An online search of the iNaturalist (2020) database resulted in no new records.

Survey efforts since the COSEWIC (2012) report include the following: Ovaska et al. (2020) reported on surveys for terrestrial gastropods in the Kootenay region from 2007 to 2015, focusing on species at risk. In September 2013, 2014, and 2015, they spent a total of 140 person-hours intensively searching for gastropods at 144 sites and detected Magnum Mantleslug (7 individuals) at 6 sites, all previously undocumented. Copley and co-workers conducted surveys for arthropods at 70 sites in 2011 (July to September), 2012 (August), 2013 (June to August), 2015 (July), and 2017 (July); all gastropods encountered were collected (C. Copley pers. comm. 2020). They detected the species (3 individuals) at 3 sites in 2011: Mount Revelstoke and 2 previously undocumented sites. Durand and Mackenzie (2017) reported on surveys by EcoLogic (2017) in the Slocan Watershed, which focused on species at risk, including gastropods; Magnum Mantleslug was not found.

Since the previous assessment, the known EOO has increased marginally (by 15.3%) with new records to the southeast near the international border and to the north, north of Revelstoke (Figure 2). The known IAO has increased by 40 km² (10 grid cells; 83.3%; Figure 2). The changes in EOO and IAO reflect increased survey efforts rather than range expansion.

The number of known subpopulations has increased from 9 to 16. Threat-based locations, corresponding to subpopulations, have also increased accordingly, from 9 to 16, assuming that each subpopulation is subjected to separate threatening events from wildfires, or recreational developments. If droughts associated with climate change are considered the most serious plausible threat, then the number of locations might be 11, combining those occurrences on the same mountains, ridges, or watercourses. Although droughts may affect large areas simultaneously, forest type, aspect, and other factors contributing to habitat heterogeneity are likely to influence their impacts on the slugs, resulting in uncertainty in the number of locations.

Population information

SAS 11 Change in number of mature individuals: unk

SAS 12 Change in population trend: unk

SAS 13 Change in severity of population fragmentation: no

SAS 14 Change in trend in area and/or quality of habitat: no

SAS 15 Significant new survey information: no

Explanation:

Survey efforts have focused on obtaining information on distribution. There is no information on population abundance or trends. Habitat quality is projected to deteriorate due to numerous threats. Logging, in particular, continues to fragment and alter habitats across the species’ Canadian range. Severe fragmentation was previously considered “possible” but is more accurately assessed as “unknown.” It is impossible to assess the viability of subpopulations based on available data. None of the surveys to date have attempted to estimate abundance and minimum viable population size for the species is unknown.

Threats

SAS 16 Change in nature and/or severity of threats: no

Explanation:

Magnum Mantleslug continues to face a multitude of threats, as identified previously (COSEWIC 2012). Threat calculator results presented in COSEWIC (2012) were re-evaluated as part of the preparation of the provincial management plan for Kootenay slugs (see Table 6 in BCECCS 2018). This evaluation resulted in some changes to the scores based on updated information on the distribution and threats. The changes are due to more realistic scoring as the process has evolved rather than a change in the actual threats. Logging (Biological Resource Use; Threat 5.3) and habitat shifts, droughts, and storms and flooding (Climate Change and Severe Weather; Threats 11.1, 11.2, 11.4) remained the greatest threats to the species, but the threat impact of both categories was reduced from Medium and Medium-Low, respectively, to Low. Other threats, also scored as Low impact, accrued from the development of ski hills and recreational areas (Residential and Commercial Developments; Threats 1.1, 1.3); introduction and spread of invasive gastropods, earthworms, and other invertebrates (Invasive and Other Problematic Species; Threat 8.1); wildfires (Natural System Modifications; Threat 7.1); quarrying (Energy Production and Mining; Threat 3.2); and road building (Transportation and Service Corridors; Threat 4.1). Forestry effluents and air pollution (Pollution; Threats 9.3, 9.5) were flagged as threats of unknown impact. Based on the cumulative impacts of all threats, the overall threat impact was calculated as Medium, as opposed to High in the previous threat calculator assessment.

Protection

SAS 17 Change in effective protection: no

Explanation:

In total, 31.8% of known occurrences are in protected areas (Mount Revelstoke National Park, Wells Gray and Stagleap provincial parks, and Darkwoods Conservation Area by Nature Conservancy Canada). The species’ presence in these areas was previously documented (COSEWIC 2012). Most occurrences are on BC Crown forestry lands (45.5%), followed by recreational (18.2%) and private forestry (4.5%) lands.

The objectives of the provincial management plan (BCECCS 2018) include securement of habitat for extant subpopulations, mitigating threats, and restoring habitat connectivity. These objectives have yet to be achieved, and it is unknown whether any of the recommended actions have been initiated (by November 2020).

Rescue effect

SAS 18 Change in evidence of rescue effect: no

Explanation:

Several records exist from the vicinity of the international border, including two recent records from the Purcell Mountains just north of the border abutting Kootenai National Forest in the United States. However, as stated in COSEWIC (2012), while rescue from the United States is possible, it is unlikely over the short term given the poor dispersal ability and patchy distribution of the slugs in the landscape.

Quantitative analysis

SAS 19 Change in estimated probability of extirpation: unk

Details:

Insufficient data for analysis

Summary and additional considerations [e.g., recovery efforts; summarize exactly what has changed since the previous assessment]

Since the previous COSEWIC assessment (COSEWIC 2012), the species has been listed as Special Concern in Schedule 1 of the Species at Risk Act in 2017. Survey efforts have increased the known occurrences (that is, sites) from 13 to 22, and the number of subpopulations from 9 to 16. The EOO has increased only marginally (15.3%), whereas the IAO has increased by 83.3%. Undocumented occurrences probably exist, but it is likely that the distribution will remain very patchy. A multi-species provincial management plan for Kootenay slugs, including Magnum Mantleslug, has been prepared (BCECCS 2018). The plan describes several actions for protecting habitats and reducing threats at known sites and for filling in knowledge gaps on the distribution and habitat requirements of the species. These actions have yet to be implemented.

Acknowledgements

Claudia Copley and Robert Forsyth generously shared their respective data on distribution records and search efforts in the Kootenay region. Heidi Gartner provided records of the species in the Royal British Columbia Museum’s collection. Lea Gelling and Katrina Stipec provided records from the BC Conservation Data Centre database. Sydney Allen (COSEWIC Secretariat) prepared the distribution maps and EOO and IAO calculations for this report. Dwayne Lepitzki, Co-chair of the COSEWIC Mollusc Species Specialist Subcommittee, and anonymous reviewers provided helpful comments on an earlier draft.

Authorities contacted

Canadian Wildlife Service:

• Rhonda Millikin
• COSEWIC Secretariat: Sonia Schnobb and Jenny Wu (ATK), Sydney Allen (mapping)
• Parks Canada: Pippa Shepherd, Species-at-Risk Coordinator; Shelley Pruss, Ecosystem Scientist; Laura Gardiner, Resource Management Officer; Lisa Larson, Ecological Integrity Monitoring Coordinator
• Province of British Columbia: Jennifer Heron, Invertebrate Specialist and Recovery Team, Vancouver; Lindsay Anderson, Rare and Endangered Species Biologist, Nelson; Lea Gelling and Katrina Stipec, British Columbia Conservation Data Centre, Victoria
• Royal British Columbia Museum: Heidi Gartner, Collections Manager, Molluscs; Claudia Copley, Collections Manager, Entomology
• Other relevant contacts: Robert Forsyth, independent, gastropod expert, Vancouver, British Columbia; Ian Adams, independent wildlife biologist, Cranbrook, British Columbia; Virginia Hudson, Manager of Conservation Planning and Stewardship, Nature Conservancy of Canada, British Columbia Region

Information sources

BCECCS (BC Ministry of Environment and Climate Change Strategy). 2018. Multispecies Management Plan for Magnum Mantleslug (Magnipelta mycophaga), Pygmy Slug (Kootenaia burkei), and Sheathed Slug (Zacoleus idahoensis) in British Columbia. B.C. Ministry of Environment Climate Change Strategy, Victoria, British Columbia. 55 pp.

Copley, C., pers. comm. 2020. Email correspondence to Kristiina Ovaska, October 2020. Collections Manager (entomology), Royal British Columbia Museum, Victoria, British Columbia.

COSEWIC (Committee on the Status of Endangered Wildlife in Canada). 2012. COSEWIC assessment and status report on the Magnum Mantleslug Magnipelta mycophaga in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa, Ontario. x + 41 pp.

Durrand, R., and R. Mackenzie. 2017. Species-at-Risk in the Slocan Watershed. Report prepared for Slocan Solutions Society. Website: https://slocanriverstreamkeepers.files.wordpress.com/2016/04/slocan_sar_report_30jan2017_final.pdf [accessed 30 October 2020].

EcoLogic Environmental Consultants. 2017. Terrestrial Ecosystem Mapping of the Willa Project. Prepared for MX Gold. Cited in Durrand and Mackenzie (2017).

iNaturalist. 2020. Observations: Magnum Mantleslug (Magnipelta mycophaga). Website: https://www.inaturalist.org/taxa/224381-Magnipelta-mycophaga [accessed December 2020].

NatureServe. 2021. NatureServe Explorer: an online encyclopedia of life [web application]. NatureServe, Arlington, Virginia. Website: https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.117721/Magnipelta_mycophaga [accessed 15 June 2021].

Ovaska, K., L. Sopuck, and J. Heron. 2020. Surveys for terrestrial gastropods in the Kootenay region of British Columbia, with new records and range extensions. Canadian Field-Naturalist 133:221–234.

Writer of status appraisal summary:

• Kristiina Ovaska

Technical summary

Scientific name: Magnipelta mycophaga

English name: Magnum Mantleslug

French name: Limace à grand manteau

Range of occurrence in Canada: 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)

>1 yr

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

Inferred and projected decline most likely based on 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].

Unknown

[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?

1. partially (habitat alteration by logging)
2. partially
3. no

Are there extreme fluctuations in number of mature individuals?

Unknown

Extent and occupancy information

Estimated extent of occurrence (EOO)

47,040 km²
(minimum convex polygon method)

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

88 km²
22 2x2 km grid cells (includes all records)

Is the population “severely fragmented” that is, 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?

1. Unknown
2. Yes

Subpopulation sizes and their viability are unknown: 16 isolated subpopulations (22 sites), most of which are known from one record only, representing 1 to 4 individuals.

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

11 to 16; minimum based on climate change (droughts) as the most plausible serious threat and groupings of sites on same mountains, ridges, or watercourses together; maximum based on the number of subpopulations (that is, sites >1 km apart in fragmented habitat or >3 km apart in continuous habitat), assuming that each is subjected to separate threatening events from logging, wildfires, and recreational developments.

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

No observed decline (known EOO has increased due to search effort). Decline could be projected due to threats.

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

No observed decline (known IAO has increased due to search effort). Decline could be projected due to threats.

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

Yes, projected decline most likely based on threats.

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

Yes, projected decline most likely based on threats.

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

Yes, inferred and projected decline in habitat quality based on 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 COSEWIC Definitions and Abbreviations website and IUCN for more information on this term.

Number of mature individuals (in each subpopulation)

Subpopulations (give plausible ranges);

Sixteen known subpopulations; an increased from nine in previous status report, reflecting increased search effort

N mature individuals total:

Insufficient data to determine.

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 November 2017 as part of the preparation of the provincial management plan (BCECCS 2018). Calculated impact for all threat categories was Low, cumulatively resulting in a Medium overall threat impact.

1. Biological Resource Use (Logging and wood harvesting; Threat 5.3)
2. Climate Change and Severe Weather (Habitat shifting and alteration, Droughts, Storms and flooding; Threats 11.1, 11.2, 11.4)
3. Residential and Commercial Development (Tourism and recreational areas; Threats 1.1, 1.3)
4. Energy Production and Mining (Mining and quarrying; Threat 3.2)
5. Transportation and Service Corridors (Roads; Threat 4.1)
6. Natural System Modifications (Fires and fire suppression; Threat 7.1)
7. Invasive and Other Problematic Species (Invasive/non-native alien species; Threat 8.1)

What additional limiting factors are relevant?

Naturally patchy habitats; poor dispersal ability

Rescue effect (immigration from outside Canada)

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

Idaho: S2 – imperilled; Montana: S2S3 – critically imperilled to vulnerable; Washington: S2 – imperilled (NatureServe 2021)

Is immigration known or possible?

Possible but limited by poor dispersal ability of slugs and their patchy distribution

Would immigrants be adapted to survive in Canada?

Yes

Is there sufficient habitat for immigrants in Canada?

Probably

Are conditions deteriorating in Canada?⁺

Yes

Are conditions for the source (that is, outside) population deteriorating?⁺

Unknown

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? No

Status history

COSEWIC status history:

Designated Special Concern in May 2012. Status re-examined and confirmed in December 2022.

Status and reasons for designation

Status: Special Concern

Alpha-numeric codes: Not applicable.

Reasons for designation: The large slug species, up to 80 mm in length, is endemic to the northern Columbia Basin in western North America. Half of the global range is in southeastern British Columbia. The species occurs in patchy habitat and is confined to moist, cool microsites within coniferous forests at mid-to high elevations. Despite extensive searches, there are only 22 subpopulations recorded within its Canadian range. Fragmentation of its habitat continues to be a threat, as are logging and habitat shifts, droughts, storms, and flooding. It may become Threatened if threats are neither reversed nor managed with demonstrable effectiveness and is currently close to meeting Threatened criteria.

Applicability of criteria

Criterion A (Decline in total number of mature individuals):

Not applicable. Insufficient data to calculate inferred population decline.

Criterion B (Small distribution range and decline or fluctuation):

Not applicable. Nearly meets the thresholds for Threatened, B2. While the EOO of 47,040 km² is above the threshold for Threatened, the IAO (88 km²) is well below the threshold for Endangered. The species probably does not undergo extreme fluctuations and is not severely fragmented, although subpopulations are isolated. It occurs at slightly more than 10 locations; the number of mature individuals, IAO; the number of subpopulations and locations are projected to continue to decline and there is an implied and projected continuing decline in area, extent, and quality of habitat.

Criterion C (Small and declining number of mature individuals):

Not applicable. Insufficient data to determine number of mature individuals.

Criterion D (Very small or restricted population):

Not applicable. Number of mature individuals is unknown and typical thresholds for D2, Threatened are exceeded (>5 locations and IAO >20 km²).

Criterion E (Quantitative analysis):

Not applicable. Analysis not conducted.

Figure 1. Distribution of Magnum Mantleslug (Magnipelta mycophaga) in Canada, showing localities known at the time of the previous COSEWIC (2012) status report and new localities documented since then. Lack of recent records from large areas of the distribution reflects paucity of search effort. Map prepared by Sydney Allen (COSEWIC Secretariat).

Figure 2. Extent of Occurrence (EOO) and Area of Occupancy (IAO) for Magnum Mantleslug (Magnipelta mycophaga) in Canada, based on all records, as compiled in 2020. Map prepared by Sydney Allen (COSEWIC Secretariat).

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 (2022)

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)*

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)**

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

Data Deficient (DD)***

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.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.

** Formerly described as “Not In Any Category”, or “No Designation Required.”

*** 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.

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