Narwhal (Monodon monoceros) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

Narwhal populations in Canada may be limited or threatened by hunting activities, environmental contaminants, industrial activities such as commercial fishing, and climate change. The effects of these factors are mitigated by the species’ deepwater habits and widespread geographical distribution, much of which is outside normal hunting areas in offshore pack ice and in isolated areas of the Arctic. This remote distribution protects large numbers of narwhals from hunters as well as isolated oil spills or other events. However, under exceptional circumstances, such as large ice entrapments or when killer whales drive narwhals into shallow water, many animals can be hunted at once from a single locality. The question of whether narwhals that summer in isolated areas serve as a reserve for those in more accessible areas, where they are more vulnerable to extirpation, remains unanswered. Narwhals are not seen as direct competitors with humans for resources, or as a physical threat.

Hunting

Hunting activities probably represent the most consistent limiting factor and threat to narwhal populations in Canada. Inuit residents of 13 communities hunt animals from the Baffin Bay population, while the Hudson Bay narwhals are hunted mainly by residents of Repulse Bay and sometimes by residents of 6 other communities (Table 1). Narwhal are also hunted by the Kugaaruk community following the community-based management system, while Taloyoak and Gjoa Haven have a yearly limit of 10 narwhals each.

Most narwhals are harvested in July and August (Donaldson 1988; Gamble 1988; Guin and Stewart 1988; J. Pattimore, pers. comm. 1986). The hunts begin earlier in the year in Pangnirtung (April), Pond Inlet and Arctic Bay (May) and end later in the year in Clyde River and Qikiqtardjuak (October). The actual number of narwhals killed during these hunts is higher than the number landed, but unknown because few data were collected on the number of animals that were killed and lost. These losses vary depending upon the location, weather, hunter experience, and type of hunt (e.g. floe edge, ice crack, open water). They also vary from year to year. Thus loss rates cannot be extrapolated from one season to another or from one community to another (Weaver and Walker 1988; Roberge and Dunn 1990).

Loss rates are typically highest at the floe edge and lowest during the open water hunt (Roberge and Dunn 1990). Comparison of these rates between studies is confounded by the fact that some studies considered only whales killed and lost, while others also considered whales that were wounded and escaped. The former method tends to underestimate the total kill, and the latter to overestimate it. These two extremes provide a range within which the actual loss rates should lie. Loss estimates from the community-based management hunts in 2001 suggest that on average at least 19 (SD 11; killed and lost only) and perhaps as many as 46 (SD 5; killed and lost plus struck and escaped) animals are lost for every 100 landed (Table 2). These crude annual loss rate estimates are comparable to those from earlier studies, most of which were for portions of the annual hunt (e.g. Hay and Sergeant 1976; Finley et al. 1980; Kemper 1980; Finley and Miller 1982; Weaver and Walker 1988; Roberge and Dunn 1990). The collection of struck and lost data is a key contribution of the community-based management program to improving estimates of hunting mortality.

Losses result in part from the fact that narwhals are often shot before they are harpooned (Bruemmer 1971; Stewart et al. 1995). Loss rates are greater among animals that are not harpooned (Gonzalez 2001). In 1979, Pond Inlet hunters tried using harpoon guns to reduce loss rates. This technology proved to be much less practical than .303 calibre rifles and hand-thrown harpoons for killing and securing narwhals (Finley and Miller 1982). In the Pond Inlet area, a high proportion of harvested animals have old bullet wounds (42% Finley et al. 1980; 23% Finley and Miller 1982). Many of the communities participating in community-based management require hunters to use harpoons as a means of reducing the number of whales that are struck and lost (M. Wheatley, pers. comm. 2003).

There is strong economic pressure to land tusked males despite a preference for the maqtaq of juvenile narwhals (Reeves 1992a). This selection is more successful during on-ice hunts in the spring when the narwhals are shot at close range and the tusk is clearly visible, than during open-water hunts (Reeves 1976). Hunter preference for large-tusked males likely leads to underestimates of numbers of females killed, given that hunters may expend more effort to retrieve male carcasses (Weaver and Walker 1988; Roberge and Dunn 1990).

Lack of reliable age data for narwhals prevents accurate prediction of reproductive and survival rates and thereby sustainable hunts. Sergeant (1981) assumed the sustainable annual hunting rate for narwhals was 5% based on studies of beluga. A more reasonable estimate is probably 3-4% given that the 5% estimate did not incorporate natural mortality (Kingsley 1989). The latter assumes that an equal proportion of male and female narwhals are killed. A bias towards males as seen at Pond Inlet (2:1 Weaver and Walker 1988) and Arctic Bay (3:1 Roberge and Dunn 1990), might increase the sustainable hunting rate, but a bias towards females should reduce it. The extent or direction of this bias over time will likely reflect trends in the price of tusk ivory and, to a lesser extent, maqtaq. Given the uncertainties related to reproductive and survival rates, and the species’ vulnerability to unpredictable mass mortality from entrapment in the ice, a more precautionary hunting rate would be 2% (DFO 1998a).

Over the period 1988 through 2001, Canadians landed an average of 327 (SD 85; range 234-547) narwhals annually from the Baffin Bay population, and 40 (SD 43; range 6-161) from the Hudson Bay population. The number of narwhals landed annually from the Baffin Bay population fluctuates widely each year, but removals due to hunting have likely increased recently in both Canada and Greenland (Figure 5; JCNB/NAMMCO 2001). However, Greenland kills may not be relevant based on recent information that suggests that Canadian populations of narwhal do travel to Greenland.

Landings from the Hudson Bay population increased from an average of 22 (SD 9.7) whales per year over the period 1979-1998 to an average of 109 (SD 51) whales per year over the period 1999-2001(Table 1). Unusually large numbers killed by Repulse Bay hunters are responsible for this increase. Repulse Bay may have removed between 5.2 and 6.9% of the Hudson Bay narwhal population in 1999 based on the 2000 survey estimate of 1780 narwhals in the Hudson Bay population (P. Richard, pers. comm. 2002), assuming that at least 50% of the whales may have been submerged and therefore missed by the survey, assuming an annual rate of increase of 4%, and using the community-based mortality estimates (186-254 narwhals; Table 2). Indeed, population mortality in 1999 may have been higher given that predation by killer whales contributed to the hunters’ success. The effects on population structure of this simultaneous removal by hunters, who prefer tusked males, and killer whales, that appear to prefer non-tusked narwhals, are unknown. Hunters from the community may also have removed between 3.6 and 4.7% of the population in 2001, when they filled the community-based management hunting limit of 100 narwhals.

The Hudson Bay narwhal population is unlikely to support the rates of removal seen in 1999 and 2001 over the long term, unless the natural rate of increase is greater than 5% per year. In 2002, the community-based management program responded to this concern by reducing the annual harvest limit for Repulse Bay from 100 to 72 narwhals. If the population is smaller than the estimate (i.e. including a correction for submerged animals), or if the natural rate of increase is less than 4%, then the population would be at risk if communities that hunt narwhals from the Hudson Bay population approach their annual limits on a regular basis. Past experience suggests this is unlikely to occur, but it must be monitored (Table 1). Evidence of unusually high mortality from causes other than hunting, such as killer whale predation or ice entrapment, must also be considered when hunting limits are adjusted.

Contaminants

Elevated concentrations of cadmium and mercury have been found in the tissues of narwhals taken in Canada and Greenland (Wagemann et al. 1983, 1996, 1998; Hansen et al. 1990). These metals accumulate in soft tissue as the animal grows but the lack of age data and small sample sizes make it difficult to identify trends in their accumulation over time and space. Within these limitations, the tissue concentrations of cadmium in narwhals taken at Pond Inlet do not appear to have changed over the period 1978-79 to 1992-94, but total mercury concentrations in the muscle, liver, and kidney may have increased (Wagemann et al. 1996). The effects of age and dietary differences and the contribution of anthropogenic mercury could not be quantified. Concern has been raised about the potential for kidney damage in narwhals from elevated cadmium levels and about the risk to human health from consuming narwhal maqtaq and meat containing elevated mercury concentrations (Wagemann et al. 1996; 1998).

In 1982-83, the blubber and liver of narwhals collected at Pond Inlet were analyzed for organochlorine pesticides (DDT, chlordane, polychlorinated camphenes [PCCs], dieldrin, hexachlorocyclohexanes [∑HCH], mirex), polychlorinated biphenyl congeners (PCBs), and chlorobenzenes (∑CBz) (Muir et al. 1992). Their mean ∑PCB concentrations were 6- to 15- fold lower than in dolphins from the Canadian east coast and belugas from the St. Lawrence River estuary, respectively, while PCC levels were from 4- to 2- fold lower, and ∑HCH, dieldrin and ∑CBz differed by <2-fold. The pattern of these contaminants in their tissues suggests that narwhals are exposed to proportionally more volatile compounds, likely by long range transport, and may have less capacity to metabolize some of these compounds than do odontocetes living nearer sources of these contaminants. No temporal trends have been identified in the accumulation of organochlorine contaminants in narwhal.

Industrial development

Recent development of the turbot (Greenland halibut) fishery in Baffin Bay has raised concern among narwhal researchers (Heide-Jørgensen et al. 2002). This fishery takes place during the open water season in the same area where narwhals winter. While it is not coincident with narwhal occupation, it is targeting fish that narwhals eat at depths of 1000 to 1300 m where they feed. The total allowable catch (TAC) rose from 300 tonnes annually from NAFO Div. OA in 1996 to 2000 (Treble 1999), to 4,000 tonnes for NAFO Div. OA and 1A (offshore) in 2001 (Treble and Bowering 2002), and is expected to increase to 8,000 tonnes in 2003 (M. Treble, pers. comm. 2002). The effects of this new competition for food resources on wintering narwhals are unknown and worthy of study. Narwhals have been captured in fishing nets (Mitchell 1981), but this is not common and of lesser concern than the effects of competition for food.

Large quantities of turbot are also caught in the spring through the landfast ice in Cumberland Sound (Topolniski 1993; Stewart 1994) when narwhals are on their wintering grounds. This longline fishery began in 1986 and targets fish at depths of 600 to 1125 m. Catches have exceeded 430 tonnes but have been in the 250 tonne range in recent years (M. Treble, pers. comm. 2002). Their effect on narwhals is unknown. Exploratory turbot fisheries have been conducted by a number of other communities in the Baffin region but they have not identified populations that will support a commercial harvest (Stewart 1994).

Threats posed to narwhals in Canadian waters by hydrocarbon and mineral development and exploration are low at present. Indeed, there is less hydrocarbon exploration ongoing in the High Arctic today than there was in the 1970s and 1980s (D.G. Wright, pers. comm. 2002), and both of Canada’s High Arctic metal mines closed in September 2002 (M. Wheatley, pers. comm. 2003). This will reduce the effects of ice breaking activities on narwhals entering Lancaster Sound in the spring. It will also reduce seismic and noise disturbances related to mining activities and the risk of hydrocarbon and heavy metal pollution. Future developments could reverse this trend.

Climate change

The potential effects of climate change on the narwhal have not been examined in detail but given the species’ close association with consolidated pack ice and dependence on small leads and cracks, such analysis should be a priority. Climate change has the potential to alter the distribution, duration, and quality of seasonal ice cover in the Arctic and thereby the density of ice-associated prey species of marine mammals, such as Arctic cod and sympagic (with ice) amphipods (Tynan and DeMaster 1997).

In the long term, global warming may result in increased visitor numbers and activities in the Arctic (such as whale watching) that may disturb and affect narwhals. It is also possible that reduced ice coverage may make narwhals more susceptible to predation by killer whales. Overall, the effects of climate change on sea ice in areas presently inhabited by narwhals are uncertain (Maxwell 1999). Indeed, the duration of ice cover in Baffin Bay and Davis Strait increased between 1979 and 1996 (Parkinson 2000). The capacity of the narwhal to adapt to changes in pack ice is also unknown (Heide-Jørgensen et al. 2002). Given this uncertainty and the fact that changes in ice cover and dynamics might alter the species’ seasonal distribution, geographical range, migration patterns, nutritional status, reproductive success, and ultimately the abundance and stock structure, the narwhal’s vulnerability to climate change deserves attention.