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Unimak Caribou Herd
Ongoing Issues — FAQs
Why did the herd decline?
We do not have enough data to determine exactly what factors caused the initial decline. It was likely a combination of unfavorable weather events in the presence of fairly high levels of predation. This pattern, where weather events reduce survival and calf production and predation exacerbates the decline and keeps the herd from recovering, has been observed for other herds in Alaska. There was no indication that the herd was at too high a density or that disease or other factors were responsible. The continuation of the decline more recently is associated with a high rate of calf mortality that can be attributed to predation. Nutritional limitations and unfavorable weather do not appear to be playing a role at this time based on the body condition of the caribou and on calf weights.
Did non-resident sport hunters cause the low numbers of bull caribou on Unimak?
Hunting did not cause the decline in the numbers of bulls. It is true that the bulk of the reported harvest in the last 10 years was from non-residents. But our analyses – and those provided in the USFWS EA – clearly demonstrate that bulls were lightly harvested for the 10 years prior to closing the season. Bull numbers continued to decline after hunting was closed. The decline in bulls is due to very low recruitment (that is, very low numbers of calves surviving to four months of age). Because bulls do not live as long as cows and have lower survival rates even without hunting, bull numbers decline faster than cow numbers when no recruits are being added to the population.
How do you know predation is limiting calf recruitment?
Our surveys indicated that calves were being born healthy but based on subsequent surveys and a limited calf mortality study; all indications were that calves died in early summer. Studies in adjacent herds indicated that early mortality is predominately caused by bears and wolves. The very same patterns observed on Unimak were observed for the Southern Alaska Peninsula herd where the selective reduction of a small number of wolves resulted in a large increase in calf recruitment.
Bears kill caribou calves. Why isn’t the state proposing to reduce bear numbers?
Our research and management on the adjacent Southern Alaska Peninsula herd (SAP) clearly showed that reducing wolves alone could provide a substantial increase in calf recruitment. Even during and after wolf removal when calf survival was high, wolves on the SAP killed more calves than bears. Bears occur at high densities in southwest Alaska, but an individual bear kills very few caribou calves there. We would have to remove about 30 bears to have the same effect on caribou calf survival as by taking a single wolf. Our observations are that Unimak appears in every way to be very similar to the SAP herd.
Aren’t these population fluctuations natural? Won’t the caribou come back as they did before?
As far as we know, the current situation is “natural.” But natural can result in no human harvest for very long periods. ADF&G is required to conserve wildlife under the sustained yield principle for the benefit of the people of Alaska, including for subsistence. Purposes of the Refuge are to conserve caribou and to provide for subsistence. The current scenario could lead to no harvestable surplus for years if not decades, failing to either conserve caribou or provide for subsistence.
Why not just wait until caribou move back across from the mainland?
We have used radio-collars to monitor caribou movements for 14 years in the UCH and the adjoining SAP herds. This has totaled 29 adults per year and 10 calves per year for a total of 546 caribou-years. Not a single individual caribou has changed herds even temporarily during that period. While they obviously have moved into new ranges in the past, the frequency of exchange is not frequent enough for management purposes.
How do you know that poor habitat did not cause the decline?
It is possible that weather events and associated poor foraging conditions in combination with predators were responsible for the initial decline. This phenomenon has been observed in other herds. Currently animals are in good condition as shown by calf weights and body condition of adults. Our professional judgment is that predation is limiting recruitment into the herd.
How do you know habitat is not currently limiting the herd?
Unimak caribou are currently in very good condition and there is no evidence of habitat limitation.
How do you know the habitat can support more caribou?
We don’t know the maximum number of caribou the island can support. However, caribou numbers are significantly below what they have been in the past so competition for existing food resources is not limiting. The state’s plan is to ensure that the population does not further decline or become extirpated due to predation. If the herd starts to grow following selective wolf removal, we will continue to monitor indices of foraging conditions (body condition, weights and pregnancy rates). If evidence of food limitation is observed, we would discontinue selective wolf removal and re-evaluate population objectives.
Don’t the subsistence hunters mostly hunt on the mainland?
Residents of the area are opportunistic and hunt where caribou are available. However, both the NAP and the SAP herds are currently closed to all hunting due to population declines. Use of the UCH for subsistence probably increases when caribou are abundant there and when they are scarce elsewhere. The Federal Subsistence Board and the Alaska Board of Game have both identified the UCH population as being important for subsistence.
Didn’t the USFSWS’ Notice of Decision indicate that local residents of False Pass were not in support of removing wolves to increase caribou?
In the Notice of Decision, the Service noted that one comment was received from a False Pass resident supporting the No Action Alternative and that no comments were received from Nelson Lagoon or Sand Point residents. In fact, the Service received comments supporting the reduction of wolves from at least 9 year round adult residents of False Pass (the majority of adult residents) but did not reference their comments in the Notice of Decision.
Why not just transplant bulls from the adjacent SAP herd?
The transplanted bulls will eventually die without contributing to increases in recruitment if predation is not reduced on calves. More bulls would have to be transplanted from the SAP, which will further delay the SAP reaching huntable status. Although translocating bulls to Unimak may result in a few more calves being born, calf survival will remain low, and the increase in calf numbers might not result in an increase in calf recruitment due to the high rate of predation. The end result would be taking away bulls and therefore reducing hunting opportunities, including subsistence, from the SAP with potentially no significant change to the status of caribou on Unimak.
The refuge is federally designated wilderness. Why not used ground-based methods to reduce wilderness impacts?
The impacts to wilderness character for predator reduction are not much different than those from the aircraft supported 3-year study of caribou - supported by USFWS - on the island. A ground-based wolf reduction program would simply be less effective and take longer than airborne efforts. The USFWS, with the assistance of ADF&G, did include a ground-based alternative in the EA but it was not selected and no rationale was provided for not selecting that alternative.
Would the use of helicopters impair the wilderness characteristics of the Refuge?
Yes, the use of helicopters would temporarily impair wilderness characteristics for short periods of time. The USFWS conducted a Draft Minimum Requirements Analysis that determined the use was acceptable for the benefits it provided in restoring the caribou herd, as is allowed under federal wilderness policy. Far more extensive use of helicopters has been allowed in this same refuge to spread poison to eliminate rats. However, Service officials reversed their decision in the Notice of Decision. In addition, the disturbance would not be much more than that caused by the associated research conducted with helicopters that is still supported by the USFWS (see FAQ #12). In any case, the total amount of disturbance by helicopters is small and is approved in other federal wilderness areas in the state.
Where is the science?
The scientific basis for the EA and the recommendations within are cited below. More references can be found on the Intensive Management - Predator-Prey References page.
In the EA, as ADF&G did in its earlier Environmental Review, the USFWS concluded that wolf reduction was necessary to restore the herd for harvest. Federal officials changed their final position only after re-assessing multiple policies and positions related to refuge and wilderness management. Even though the Service states that it holds subsistence equal to the other refuge purposes, the final Notice of Decision fails to support subsistence and the conservation of caribou at the expense of philosophical beliefs related to wilderness and natural diversity.
References Cited: USFWS EA, December 2010
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- Adams, L.G., F.G. Singer, and B.W. Dale. 1995. Caribou calf mortality in Denali National Park, Alaska. Journal of Wildlife Management 59:584-594.
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- Alaska Census Data 2000-2008. [On line] Beals, F.E., and J.E. Longworth. 1941. Pages 11-25 [unnumbered] in Wildlife observations from Unimak Island between Jan. and June 1941. Unpublished USFWS “sea otter” report. Smithsonian Institution Archives, Record Unit 7176, Box 5, Folder 4. [Copy in files at Alaska Maritime National Wildlife Refuge.]
- Bergerud, A.T. 1974. Decline of caribou in North America following settlement. Journal of Wildlife Management 38(4):757-770.
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- Mech, L.D. and R.O. Peterson. 2003. Wolf-prey relations. Pp.131-160. In L.D Mech and L. Boitani (eds.), Wolves: behavior, ecology, and conservation. Chicago: University of Chicago Press.
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- NOAA Fisheries: Office of Protected Species 2010. [On line] Post, E.S., and D. Klein. 1999. Caribou calf production and seasonal range quality during a population decline. Journal of Wildlife Management 63:335-345.
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