Beluga whale (Delphinapterus leucas) COSEWIC assessment and status report: chapter 11
Limiting Factors and Threats
- St. Lawrence Estuary Population
- Ungava Bay Population
- Eastern Hudson Bay Population
- Western Hudson Bay Population
- Eastern High Arctic – Baffin Bay Population
- Cumberland Sound Population
- Eastern Beaufort Sea Population
Limiting factors may be viewed as belonging to two main categories; those which would generally be classed as natural and those which are anthropogenic.
Causes of natural mortality of Arctic mammals are difficult to document because animals may live far from human populations and carcasses are rarely ever found. The chance of finding dead mammals that live in the marine environment is even smaller. Here the combined scientific and aboriginal traditional knowledge (ATK) is relatively scarce and quantitative data are lacking. One exception to this is the beluga population in the confines of the St. Lawrence Estuary where ongoing long-term studies have gained considerable knowledge of disease and mortality factors from the recovery of dead carcasses (Martineau et al. 2002a, b)
Polar bears, Ursus maritimus, are a known predator of belugas throughout their Arctic range. They are known to kill belugas in the winter along the floe edges. At break-up, polar bears have been observed to take belugas by diving in on top of them from platforms of floating ice (Smith and Sjare 1990). During the open water season, polar bears are capable of killing belugas that have become entrapped in river streams when the tide has ebbed (Norris 1994).
Ice entrapments (savsaat, pl. savsait) of belugas are known to recur in several areas of the Beaufort Sea, Canadian High Arctic, in northern Foxe Basin and along the West Greenland coast. Polar bears and Inuit hunters take advantage of these incidents to harvest belugas. The proportion of mortality in these situations that is attributable to predation is not well documented and remains debatable (Kilabuk 1998).
Killer whales, Orcinus orca, are known to take belugas throughout most of the eastern Canadian Arctic (Reeves and Mitchell 1989) and Greenland (Thomsen 1993). Observations of killer whale occurrence are fewer in the high Arctic and the Beaufort Sea areas, but occasional sightings (Byers and Roberts 1995) and attacks have been documented. In the St. Lawrence Estuary, killer whales might have once been somewhat more abundant than in the present day, when almost no sightings are made, even in the outer Gulf of St. Lawrence. One observation was made of killer whales killing belugas as far upstream as Les Escoumins in the early 1960s (L. Otis pers. com. 1967). No such incidents have been seen in the last 15 years, during which intensive beluga research has been conducted (R. Michaud, pers. com. 2002)
The Inuvialuit of the Mackenzie Delta mention that belugas are frightened of walruses, Odobenus rosmarus, and have possibly documented a wound resulting from a walrus tusk (Byers and Roberts 1995). There has also been an incident of a beluga that was found with the broken tip of a narwhal, Monodon monoceros, tusk imbedded in its melon (Byers and Roberts 1995, Orr and Harwood 1998). This might be indicative of aggressive interspecific behaviour (Reeves and Mitchell 1988), which could result in mortality. Belugas and narwhals occupy some of the same areas during the open water season in the Canadian High Arctic (Smith et al. 1985, Innes et al. 2002b).
The strong philopatry of belugas, which causes them to return to the same estuaries year after year, makes them highly vulnerable to overexploitation. This behavioural trait is undoubtedly the most important natural factor which has led to the extirpation of beluga populations by a combination of commercial and subsistence hunting (Francis 1977, Reeves and Mitchell 1987). Because of this strong philopatry and site tenacity (Caron and Smith 1990) native harvesters, hunting in these estuaries, continue to perceive that the numbers of belugas remain high even though the populations might actually be declining.
Little is known of the role of infectious diseases in belugas. Recently, Brucella antibodies have been found in the tissues of Beaufort Sea animals, but no indications have been found that this has caused health problems at the population level. WhÎle viruses have been known to cause large-scale die-offs of seals and toothed whales (Hinshaw et al. 1984, Lipscomb et al. 1994), no such event has yet been documented for any known beluga population.
Anthropogenic threats act as strong limiting factors for many of the Canadian beluga populations. They must be discussed for each population separately because they vary greatly over the wide geographical range of the beluga.
The belugas of the St. Lawrence were much reduced in numbers by hunting (Vladykov 1944, Reeves and Mitchell 1984), and also perhaps by the loss of certain estuarine habitats (Kingsley 2002). At present this is the only population of belugas in Canada that has been completely protected from hunting, first under the 1979 Beluga Protection Regulations in the Fisheries Act, and then, in 1993, under the Marine Mammal Regulations of the Fisheries Act.
The area presently occupied by these belugas is a heavily used maritime shipping corridor. The St. Lawrence Estuary also is very heavily industrialized and has the Great Lakes, an area of large industry, as its headwaters. Because of the perceived low numbers of belugas present in the 1970s and the possibility that the population was in decline (Pippard 1985), a large amount of research has been conducted on the many anthropogenic factors which might be limiting the growth and recovery of this population (see references in: Muir at al. 1990, Béland et al. 1993, Martineau et al. 2002a).
The small size and lower genetic diversity of this population has led to the speculation that inbreeding might be suppressing the reproductive rates (Patenaude et al. 1994). WhÎle the genetic diversity of this population is the lowest of all Canadian populations (de March and Postma 2003), the degree to which inbreeding suppression is a limiting factor is hard to evaluate. It should be noted that marine mammals, particularly seal populations of several species, have experienced severe reduction to very low numbers where a genetic bottleneck could have occurred and yet have rebounded to high densities. Other genetic factors, such as changes at particular loci, might be implicated in a reduced capacity of the St. Lawrence Estuary population to respond to certain pathogens (Murray et al. 1999).
The loss and perturbation of habitat is a continuing threat for St. Lawrence belugas which live in a relatively restricted zone of a heavily traveled and populated area. Both commercial shipping and whale watching activities have increased significantly in the area over the last 40 years (Michaud 1993). Lesage et al. (1999) have demonstrated that boat traffic had a significant effect on the vocal behaviour of belugas. Little is known of the immediate or chronic stress responses which belugas might have to these various disturbances factors, and how it might affect their feeding, mating and nurturing behaviour.
Large numbers of beluga carcasses have been recovered along the inhabited shorelines of the St. Lawrence Estuary and have allowed considerable research into the causes of mortality. Links have been postulated between the prevalence of cancerous tumors and the exposure of St. Lawrence belugas to industrial pollutants (Martineau et al. 2002a). Debates continue on whether such correlations between pollutants and pathologies are truly indicative of a direct cause and effect relationship, and whether the sample of recovered carcasses is representative of measured cancer rates within the live population (Theriault et al. 2002, Martineau et al. 2002a, Hammill et al. 2003). Because little information exists from Arctic beluga populations on cancer rates and since the St. Lawrence beluga cancer samples come mainly from old animals, it is difficult to evaluate this question (Geraci et al. 1987). There is no doubt that belugas of the St. Lawrence are more exposed to pollutants than any other beluga population in Canada (Muir et al. 1990).
Other possible limiting factors include competition for resources with commercial fisheries and other increasing populations of marine mammals such as harp seals, Pagophilus groenlandica, and grey seals, Halichoerus grypus, (Curren and Lien 1998). More detaÎled research must be conducted before the effect of competition can be critically evaluated (Nozeres et al. 2001), particularly since belugas eat a variety of food species (Vladykov 1944), and are capable of deep foraging dives (Martin and Smith 1992). It should be noted, however, that even with the high carcass recovery rate, no cases of starvation have been documented. Occasional extralimital sightings of belugas are reported either along the Labrador coast or south of the St. Lawrence Estuary (Curren and Lien 1998). These could be stray animals from this population, but appear to be very low in numbers. At least one such extralimital animal from Labrador was shown to belong to an Arctic population by genetic analysis (B. de March, pers. com.).
This population is so severely depleted that its recovery is uncertain. Future hydroelectric developments in Ungava Bay have recently been indicated by the Quebec government. These might have the potential to affect the river outflow into some estuaries used by Ungava Bay belugas. The Inuit of Ungava Bay have expressed concern about the effect of increased noise disturbance by both commercial shipping and outboard motors (Lee et al. 2002).
Continued overexploitation of this population by resource harvesters, at or near the present level, may lead to its disappearance within the next 10-15 years (Hammill 2001, Bourdages et al. 2002). The Eastern Hudson Bay belugas are the subject of quotas, and closed hunting seasons in certain areas under a co-management plan between Nunavik and Department of Fisheries and Oceans Canada in an effort to remedy the critical status of this population. To date however, a significant reduction in catches has not occurred (Lesage et al. 2001).
Disturbances from outboard motors and hunting in the estuaries used by belugas of this population have significantly increased over time (Doidge1994), and could also be harmful to the population. Ironically, because this disturbance appears to reduce the numbers coming to the estuaries, it might have the positive effect of reduced harvests in the long run by driving the belugas further offshore.
The Inuit of Nunavik have also expressed concern in the past, about habitat degradation of estuaries by noise disturbance and hydroelectric projects, which could affect the outflow of rivers in Eastern Hudson Bay (Doidge at al. 2002; see also Doidge and Lesage 2001).
Expanding commercial fisheries, for instance for Geenland halibut (Reinhardtius hippoglossoides; also called turbot), in the Hudson Strait, southern Davis Strait, and off the northern Labrador coast, may degrade the winter habitat of this population, as well as the Western Hudson Bay population.
This large population, centred on the Seal, Churchill and Nelson Rivers, is the subject of substantial, and rising (see above) catches, and might be subject to disturbance by increased shipping. Future hydroelectric projects could cause changes to river outflow and result in changes in the use of such sites as either moulting or feeding areas. This has not apparently been the case in the developments to date on the Churchill River.
The Eastern High Arctic – Baffin Bay population, which spends its winter in the Jones Sound – North Water polynya area, does not appear to be adversely affected by over-exploitation or subject to any other negative anthropogenic impacts. The occasional ice entrapment occurs in this area (Freeman 1968, 1973, Heide-Jørgensen et al. 2002b), which is not unexpected since belugas are living throughout the winter in an area of heavy shifting and consolidating ice. The magnitude of mortality from these events is not well documented.
Overexploitation by Greenland Inuit, who harvest belugas along the West Greenland coast, is a serious concern for the animals which winter in this area (Innes and Stewart 2002). Although commercial fisheries for Greenland halibut and pink shrimp, Pandalus borealis, take place in the area occupied by belugas in the winter, deleterious effects of competition by fisheries for resources have not yet been studied.
Inuit of West Greenland report changes in the distribution of belugas which now are found more to the west of Disko Island, and in some cases are reported to stay further offshore. Increased trawler and hunting boat traffic and drive fisheries in such areas as Upernavik have been cited as the causative influence (Thomsen 1993).
Apart from subsistence hunting pressures there are no apparent important anthropogenic impacts on this population. Commercial fisheries for Greenland halibut, Reinhardtius hippoglossoides, are conducted in the area. Belugas are known to feed on this species at the floe edge (Stewart 2001).
Inuit of Pangnirtung report changes in the behaviour of belugas related to increased boat traffic and the associated noise caused by outboard motors (Kilabuk 1998). This noise is considered the reason for the decline in numbers of belugas, which were formally more numerous in areas such as Clearwater Fiord. Hunters also note a decrease in the fatness of whales, which they relate to more energy being spent in avoidance of motorboats. Less selective hunting resulting from faster-moving motorboats is blamed for higher proportion of belugas being scarred with bullet wounds. This is seen as being exacerbated by the annual quota which obliges hunters to rush their hunting period in order to obtain their part of the catch (Kilabuk 1998). The quota was increased from 35 to 41 in 2003.
This population has been continually monitored since 1973 and is not limited by over-hunting. There does not appear to be any indication of reduced body condition or negative effects of any infectious diseases (DFO 2000). Increasing commercial fisheries in the Bering Sea wintering grounds might, in the future, impact several species of Arctic marine mammals.
Much offshore petroleum exploration has already occurred in the Mackenzie Basin, with no measurable impact on this population (Fraker 1980, Finley et al. 1987). The proven offshore oil and gas reserves are important and will be developed in the near future. This will increase anthropogenic activities and might create disturbance.
Once the oil and gas wells and pipelines are built there will also be the potential threat of oil spills. WhÎle the short-term consequences of spills on cetaceans are not necessarily always lethal, effects on the food chain are also of concern (Geraci et al. 1983, Smith et al. 1983, St. Aubin et al. 1985). If oil transport is by pipeline down the Mackenzie rather than by tanker, the chances of a major oil spill affecting belugas are much reduced.
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