Skiff-based surveys.—Skiff-based surveys were conducted several times during the 1990s at Adak, Kagalaska, Kiska, Little Kiska, Amchitka, Shemya (Semichi Islands), and Attu islands (Fig. All statistical tests were considered to be significant when P < 0.05. Softened by warming and acidifying waters, the coral-like structures have quickly succumbed to the urchins’ tiny teeth, which can annihilate years of fragile algae in a single bite. Hence, the westward extent of the decline appears to be Attu Island. We evaluated the hypothesis that otter densities varied among island groups over time. Differences in aerial and skiff-based population trends were evaluated using a paired t-test. We tested the hypothesis that otter densities varied among island groups with a 1-way analysis of variance, using island groups as treatments and islands as replicates. In 1970, Jim Estes made his first trek up to Alaska’s Aleutian Islands. Location, altitude, weather, visibility, and observer identification were recorded directly into an onboard computer interfaced with a global positioning system. “You can travel down 10 miles of coastline and never see an animal,” he said. The survey crew consisted of a pilot, copilot, 2 observers, and 1 data recorder. Tinker, A.M. Doroff, and D.M. Sea otters in the Aleutian archipelago have declined substantially in number. From 2014 through 2017, some reefs shrank by up to 64 percent. We conducted an aerial survey of the Aleutian archipelago in 2000 and compared results with similar surveys conducted in 1965 and 1992. These data, together with the uniformly low density for the entire Aleutian archipelago in 2000, suggest that the overall population is currently about 10% of the area's potential carrying capacity. The sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. One controversial hypothesis is that orcas have been eating the otters. Proportional changes were then plotted as frequency distributions and contrasted with expected distributions for stable populations, assuming sampling variation but with no prevailing tendency toward increase or decline. Overflights of Steiler sea lion haulout and rookery sites were permitted under the National Marine Mammal Laboratory's ESA/ MMPA Permit 782-1532-00. Map of the study area denoting 6 major island groups (Near, Rat, Delarof, Andreanof, Four Mountains, and Fox islands) in the Aleutian archipelago. 1). ; Estes 1990; L. Rotterman and T. Simon-Jackson, in litt. The number of sea otters counted decreased by 75% between 1965 and 2000; 88% for islands at equilibrial density in 1965. During the past 15–20 years, sea otters Enhydra lutris in the Aleutian Islands, Alaska, USA, experienced a drastic decrease in population size. “Given those two things happening simultaneously, it’s really getting hit from both sides,” said Alyssa Griffin, an ocean biogeochemist at the University of California, Davis, who wasn’t involved in the study. A. Tinker M. T. Williams T. M. Doak D. F.. Hatfield B. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. The eastward extent of the decline is less clear. The information presented in this article chronicles one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. The loss is more than cosmetic. Changes yet to come will likely prompt the grazers to pick up the pace even more, the team’s analysis showed, barring sweeping change in carbon emissions. This assessment assumes that data gathered in the 3 aerial surveys are directly comparable. You wouldn’t think sea otters would affect the climate very much, but their existence keeps other parts of the ecosystem in check. Mean encounter rates (otters/km) for the shoreline and transects were compared between 1992 and 2000 surveys. Estimated annual rates of decline at the 3 islands averaged 19.4% (±0.94) during the 1990s; hindcasting provided estimates for the start of the decline as 1988 for Adak, 1991 for Amchitka, and 1986 for Kagalska (Fig. United States Fish and Wildlife Service, Marine Mammals Management, 1011 East Tudor Road, Anchorage, AK 99503, USA. Comparison of sea otter population trends based on aerial and skiff-based surveys conducted during the 1990s at 6 islands in the Aleutian archipelago. Behavior. The aircrafts were flown approximately 0.23 km from the shoreline at an altitude of 91 m and an average airspeed of 185 km/h during the surveys, sampling an area from shoreline to approximately 0.7 km offshore (T. Evans et al., in litt.). Estimated dates for the onset of population declines of sea otters at Adak, Amchitka, and Kagalaska islands. When sea otter populations are healthy, urchin populations are kept in check, and kelp is abundant. Predecline abundance was estimated from aerial counts conducted in the late 1950s and early 1960s when populations at the islands were presumed to be at equilibrial density (Kenyon 1969), and a correction factor of 3.58 (±0.77) was applied to the counts to adjust for sightability and detection (varying this correction factor between 2 and 4 did not change the results substantively). B. Our findings are consistent with this hypothesis, given the broad geographic extent of pinniped declines across the western Gulf of Alaska and the Aleutian Islands (D. Withrow et al., in litt. The decline of the white abalone throughout most of its range over the last century, and the decline of the black abalone in the southern half of its range over the last 3 decades, had essentially nothing to do with sea otter predation. Nonetheless, the population decline appears to have been relatively recent (Figs. These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. 3d–f), the resulting distributions became unimodal and were displaced strongly to the left, indicating an overall decline of 88% (±4.6; n = 21) between 1965 and 2000 (Fig. In the past several decades, a glut of carbon dioxide in the atmosphere has acidified ocean waters, making it harder for algae to armor themselves. At the present rate of decline, the population will reach the SSORT's recommended criterion for up-listing to Endangered within two to three years. Now, Dr. Estes said, more than 90 percent of those otters are gone. Jason Henry/Special To The Chronicle The number of sea otters swimming off the California coast this year dwindled by 86 from last year, a 3 percent decline in the animal’s population, … Whereas the author of the reading states that pollution was the major cause of the decline in sea otter populations, the lecturer suggests that predation is the most likely factor contributing to the reduction in … Data from the 2000 aerial survey indicate that numbers have declined across the entire Aleutian archipelago. For many years, there were no sea otters in Canadian waters and most of the sea otters in the world were … That could be a difficult task, given the probable cause of the Aleutian Islands’ stunning vanishing of otters. We suspect that these various declines are causally linked, and thus the key to understanding the sea otter decline lies with the understanding of why pinnipeds have declined. In 1992, the survey aircraft was a deHavilland turbine Twin Otter, and in 2000 the survey aircraft was a turbine Aero Commander 690A. 1) when viewing conditions were good to excellent (Beaufort sea state of 1–2, and >1 km of clear visibility at sea level). Dr. Estes, who is 74, hasn’t visited the Aleutians since 2015. National Research Council 1996). The algae’s decline also seems to be speeding up. By 2000, sea otter densities had declined to a uniformly low level throughout the … Fishery Bulletin 103:270-279. The mean ratio was then multiplied by the aerial count to obtain a minimal estimate of current population abundance. The minimal population estimate was 8,742 sea otters in 2000. The annual percentage of decline in population density was calculated for skiff-based and aerial surveys as 100(1 − λ), where λ is the annual rate of population growth (λ = er, r = [ln(Dt+dt) − ln(Dt)]/dt, where Dt = density at year t and dt = number of years between surveys). In recent decades, the sea otter population the Aleutian Islands of western Alaska has plummeted. Remnant populations, located in the central Aleutian Islands, were monitored infrequently through the 1950s (Kenyon 1969; Lensink 1962; Murie 1959). The earliest and most extensive recovery of sea otters after the fur trade occurred in the Aleutian archipelago. This analysis is based on limited data and depends on a variety of simplifying assumptions (most importantly, that the initiation of the decline was instantaneous and that the rate of decline was constant over time). However, it suggests that the population decline began some time after the mid-1980s. 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