Atlantic walrus (Odobenus rosmarus rosmarus) recovery strategy: chapter 3
Recovery Feasibility
A self-sustaining population of Atlantic walrus exists in the eastern Arctic, adjacent to the historic range of the extirpated Northwest Atlantic population. Occasionally individuals, probably strays from the north, are observed in the historic range of the Northwest Atlantic population, but there has been no natural recovery of the southern population to date despite the cessation of the key threat (hunting) for over 200 years (COSEWIC 2006).
Accordingly, any attempts at recovery in the shorter term of this extirpated population would require the re-introduction of individuals from another area to establish a viable population.
The recovery of the extirpated Northwest Atlantic population ofAtlantic walrus is not considered feasible at this time. Based on definition of the ‘extirpated’ designation of COSEWIC, this population is no longer found in the wild in Canada and consequently, any recovery would require the introduction of non-native individuals and an examination of the assessment criteria for considering these introduced individuals. Notwithstanding this administrative issue, an fulsome examination of feasibility consideration are presented in the following sections.
2.1 Availability of Individuals for Re-establishment
Recovery would require that individuals be available to support re-establishment of a viable population. Atlantic walrus populations in Canada were recently assessed in a single designable unit as “Special Concern” by the Committee on Status of Endangered Wildlife in Canada (COSEWIC 2006). Estimates of current abundance are imprecise, but available information suggests a total walrus population in northern Canada of the order of 10,000 individuals (COSEWIC 2006). Its ability to sustain current removals is questionable however and current harvest levels are poorly known. Recent average harvests may have been of the order of 560 individuals per year, levels which may not be sustainable in some areas or throughout the range (COSEWIC 2006).
If the criteria for subsequent assessment are considered, populations of less than 250 mature individuals are considered “endangered” under the risk assessment criteria used by COSEWIC (COSEWIC 2004). Therefore, hypothetically, an introduction of well over 100 mature individuals, perhaps a minimum of 250, would be necessary to lay the basis for re-establishment of a population of Atlantic walrus in the Northwest Atlantic below the endangered risk threshold. Re-establishment over a period of time of the order of 5 years would allow individuals to build social interactions and perhaps establish a viable population. Under these assumptions, 20-50 individuals per year would have to be captured and transported to support a reintroduced population. While this level of removal in itself would not likely pose a conservation concern, addition of these removals to existing harvests would increase risk to the existing northern populations. Therefore it is uncertain that removals of individuals from the extant population for a re-introduction program would not jeopardize its status even if well managed. Furthermore, captures for re-establishment of a Northwest Atlantic population would have to be managed in concert with Aboriginal subsistence harvest. The species is important for Aboriginal subsistence and there are significant removals for that purpose. Aboriginal harvesting rights are assured by Canada’s Constitution and by the Nunavut Land Claims Agreement, but conservation requirements take priority over Aboriginal harvesting rights.
Atlantic walrus is also found in west and east Greenland and western Russia, but conservation status of these populations is such as to make removals for re-introduction in southern Canada unlikely. The west Greenland population is considered depleted and declining and is subject to subsistence harvesting, the east Greenland population may be subject to unsustainable levels of subsistence harvesting, and information on the western Russian population is very uncertain (NAMMCO 2005).
2.2 Habitat Availability
Sufficient habitat would have to be available to support re-establishment of the Northwest Atlantic walrus population, or would have to be made available through habitat management or restoration. Suitable habitats, combining relatively shallow water with productive bottom invertebrate communities, probably exist in the Northwest Atlantic area historically inhabited by Atlantic walrus, given that there are relatively large areas of relatively undisturbed habitat in this region. However, human settlements and human activities are widely distributed in these historically inhabited areas, and disturbance from these would be an important potential habitat limiting factor.
Selection of sites for re-establishment would have to be done with considerable care. Areas with minimal human settlements (to minimize disturbance), minimal human activities (fishing, shipping, recreational activities in coastal areas), minimal fisheries for bottom invertebrates, and relatively unpolluted water (to minimize contamination from and mortality in bottom invertebrates) would be required for reintroduction of this species. Consideration might be given to sites within coastal protected areas, and measures to restrict interactions between humans and walruses would have to be included in any re-introduction initiative.
2.3 Potential to Mitigate Threats to Individuals and Habitat
The potential for significant threats to the species or its habitat to be mitigated or avoided must also be considered in assessing recovery feasibility. The existing legal provisions prohibiting the harming of a listed extirpated species under the Species at Risk Act might provide a good basis for reducing threats to a re-introduced population to a minimum.
Harvesting is unlikely to be a serious threat in southern Canada, since the only harvests permitted on the extant eastern Arctic population are for Aboriginal subsistence; although it is not certain that Aboriginal rights to harvest would not be asserted, there appears to be no documented evidence of Aboriginal harvesting in the south. Cree in eastern James and Hudson Bay occasionally harvest walrus for dog meat (COSEWIC 2006), and it is possible that such use was historically made in southern Canada where walrus were found. Entanglement in fishing gear, as with whales and seals, is a potential threat which would have to be managed within any area of reintroduction of this species. Human disturbance could probably be minimized by selecting areas far from human settlements, or within established protected areas, for re-establishment.
Interactions with other species might potentially affect recovery, but the impact is impossible to assess. Predation would probably not be an issue, since even in the north predation is apparently rare and impact is reduced by herd behavior. Adequate abundance and productivity of prey species would be a critical factor to choosing a site for re-introduction.
2.4 Existence of Effective Recovery Techniques
Recovery techniques which have been proven effective would be required if this population were to be re-established. Transport of walrus by air is feasible, as has been shown by shipments of individual walrus between zoos and aquariums (Brookfield Zoo, n.d.). However, it seems unlikely that humane transport of the large numbers of walrus needed to re-establish a viable population would be feasible in the near-term, in light of the remoteness of the source areas, the size of mature animals, the numbers required, the large distances to be covered, as well as the uncertainties with survival through any potential relocation. Walrus are only found in remote areas of the north, far from normal air transport facilities, and the logistics of transporting live animals from these areas would be very difficult. In recent years walrus have become less abundant near population centers and are mainly found at some distance from settlements (COSEWIC 2006), further increasing the difficulties of humane live transport. Given the need to resettle walrus in areas of minimal human disturbance, it would be necessary to move walrus to remote areas in the historical range, further increasing complexity and distance of transport.
As indicated above, transport of 20-50 individuals per year would be required over 5 years or more to lay the basis for a re-established population. Each individual trip would require (a) live capture of a mature adult walrus in a remote Arctic area (b) holding in captivity pending transport (c) transport, probably by boat, to a local airport (d) transport by small aircraft (Twin Otter) from a local airport to Iqaluit or another airport capable of taking large aircraft (e) transport south by jet (f) transport to a large airport in the area of release (g) transport by small aircraft, vehicle or boat to the site of release. Efficiency might be increased by capturing and transporting several animals per trip. However, the logistics of such operations would be such as to make feasibility of large-scale reintroduction highly questionable.
Captive breeding is unlikely to be a viable option to support re-establishment. Although walrus can be kept in captivity; at present there are 25 individuals in 9 zoos in North America, births in captivity are very rare (Indianapolis Zoo n.d.). Few young have been raised by their mothers in captivity, but hand-rearing by humans is possible using formulated feeds (COSEWIC 2006). Intrinsic rate of population increase for walrus in the wild would be around 5% per year based on estimates of sustainable harvesting rates and on information from species with similar reproductive characteristics (large whales). A rate of increase of 5% per year translates into a population doubling time of 14.4 years. Even beginning with a captive population of 10 individuals, 4 doublings (56 years) would be required to achieve numbers of the order needed to establish a viable population (160 individuals). Risks and uncertainties for this strategy would include questionable adaptability of captive bred individuals to wild conditions, the need for extensive facilities and personnel over a very long time period for keeping and rearing large numbers of captive individuals, and uncertainties about breeding success in captivity. The need to hand-rear young and to remove tusks in captivity would reduce adaptability to conditions in the wild, and rate of increase in captivity would probably be lower than that expected in the wild, increasing the time to produce the required numbers.
2.5 Recovery Feasibility Conclusion
Recovery of the extirpated Northwest Atlantic population of Atlantic walrus is considered neither biologically nor technically feasible at the present time. There are many uncertainties about whether a viable population would establish, even if (i) adequate numbers of individuals were available for re-introduction and (ii) interactions between walruses and humans could be managed in such a way as to ensure good habitat conditions for re-introduction. It is further uncertain as to how well individual walrus would adapt from northern conditions, where ice is available for much of the year, to an area where ice is only present in winter and only in part of the historical range. Choice of site(s) for re-establishment would be critical; although some characteristics of an ideal site can be identified (minimal human disturbance, abundant benthic mollusc populations at shallow depths, good coastal habitat for haul out), it would be impossible to guarantee success at any given site. Sea otters have been successfully re-introduced to areas from which they have been extirpated, but this is a species with a high intrinsic rate of increase, in contrast to walrus. Because of the low rate of increase of walrus, efforts to re-establish a Northwestern Atlantic population of Atlantic walrus would have to be continued over at least a decade, and determining whether re-establishment was successful might well require several decades.
The biological feasibility of recovery associated with the availability of the numbers of individuals needed to re-establish a population is not certain: extant populations are at low levels, and Aboriginal subsistence harvest is a high priority in managing these populations. Although re-introduction might be considered a conservation issue, the risks and uncertainties surrounding the potential success of re-introduction in the south might make it difficult to argue that capture for re-introduction was a higher priority than harvest for Aboriginal subsistence. Technical feasibility of transporting the large numbers of walruses needed to support re-establishment of a viable population is doubtful, given the many transport steps required between the remote northern areas from which mature live animals could be obtained and of the remote southern resettlement site. The potential cost and logistics associated with a large recovery effort combined with uncertainties regarding survival through any relocation as well as the success of any re-establishment support the conclusion that recovery is not feasible at this time.
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