It’s one reason for a worrying decline in the number of California sea otters. 2). It has been hypothesized that an increase in killer whale Orcinus orca predation was the primary cause of this decline.. 2 . The minimal population estimate was 8,742 sea otters in 2000. The findings point to the importance of otters in the Aleutians, where the marine mammals act not just as predators, but protectors, maintaining biological balance through their voracious appetites. 2000; A. M. Burdin, pers. For power analyses we set α = 0.1, standard deviation equal to that observed and calculated the power to detect a medium effect size (sensu Cohen 1988), given existing sample sizes. Two or more surveys were conducted in separate years at each of these islands during the 1990s. The severity and geographic extent of this decline raise several conservation concerns. 1978; L. Rotterman and T. Simon-Jackson, in litt.). The latest count of this threatened species shows their population dropped to just 2,711, a decline of 3.6 percent. The information presented in this article chronicles one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. 1). 1 . Diverse hypotheses have been advanced to explain the pinniped declines, but their cause (or causes) remains uncertain (National Research Council 1996). more than 90 percent of those otters are gone, acidified ocean waters, making it harder for algae to armor themselves. Estimated rates of population decline during the 1990s based on skiff-based and aerial surveys of 6 islands in the western and central Aleutians were 17.7% (±2.98) and 17.5% (±2.29), respectively (Table 2). Viewed alongside each other for multiple years, the population index data points indicate trends of growth or decline in the southern sea otter population, but that is not to say anomalously high or low raw counts aren’t worthy of notice and concern. 1998). As they have disappeared, the rest of the local food web has started to crumble — a process that’s been accelerated and compounded by climate change, Dr. Estes and his colleagues report in a paper published Thursday in the journal Science. 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. “And temperature exacerbates that issue.”. Sea otter (Enhydra lutris) populations were exploited to near extinction and began to recover after the cessation of commercial hunting in 1911. We counted sea otters with the unaided eye, using binoculars to confirm sightings or to count animals in large groups. 2000; Kenyon 1969). A.. Estes J. But he holds out hope that the islands will someday boomerang back to the breathtaking ecosystem he witnessed as a young man. 1995). Population Trend (-10 to 10) 2 Distribution Trend (-10 to 10) By the early 20th century, northern sea otters were nearly extirpated from Alaska as a result of overharvest (Muto et al. This analysis was done separately for aerial survey data from 1965, 1992, and 2000. 2019). In contrast, the 1965 survey was conducted from a DC-3 aircraft flying at 222 km/h and 61–122 m in altitude, which likely reduced the probability of detecting sea otters (Kenyon 1969). By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. “The reefs are producing less dense skeletons,” Dr. Rasher said. Sea otters have not recolonized all former habitats, though their current distribution is considered stable (USFWS 2013b; Ballachey and Bodkin 2015). These findings prompted us to conduct another aerial survey of the entire Aleutian archipelago in April 2000 to assess the magnitude and geographic extent of the population decline. Population densities differed significantly among island groups in 1965 (F = 9.50, P < 0.001) and 1992 (F = 7.44, P < 0.001) but not in 2000 (F = 1.79, P = 0.138, 1 − β = 0.76). During the past 15–20 years, sea otters Enhydra lutris in the Aleutian Islands, Alaska, USA, experienced a drastic decrease in population size. The Aleutian archipelago extends westward from Unimak Pass to Attu Island (Fig. Sea otters, which can eat nearly 1,000 sea urchins a day, have seen their numbers along Alaska’s Aleutian Islands shrink by 90 percent in recent decades. 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. Population trends from a time series of skiff-based counts documented a precipitous decline in sea otter numbers at Adak Island during the early to mid-1990s, and subsequent surveys at Little Kiska, Amchitka, and Kagalaska islands indicated similar declines (Estes et al. Aerial surveys were funded by the United States Fish and Wildlife Service, United States Geological Survey, and United States Navy. Counts were recorded separately for each section. The mean ratio was then multiplied by the aerial count to obtain a minimal estimate of current population abundance. J. Bodkin, A. DeGange, D. DeMaster, J. Gittleman, R. Meehan, B. Miller, R. A. Powell, and an anonymous referee provided information or commented on drafts of the manuscript. From 2014 through 2017, some reefs shrank by up to 64 percent. Refinement of these trends is limited by a paucity of information for the 27 years that passed between the 1965 and 1992 aerial surveys (Estes 1990; Estes et al. Decline in sea otter (Enhydra lutris) populations along the Alaska Peninsula, 1986-2001. Frequency distributions of proportional changes in abundance (Nt2/Nt1) of sea otters among islands in the Aleutian archipelago, a-c) All islands surveyed during both years for which ≥20 otters were counted during at least 1 survey and d-f) only for those islands which were at or near K (defined as the population status when growth ceased because of resource limitation) in 1965. With the decline of the sea otter, the urchin population has skyrocketed, leading to diminishing kelp forests. Southwest Alaska's sea otters, which came back from the brink of extinction in the 1800s, are facing another dramatic decline and could be named a "threatened" species as early as Tuesday. These estimates did not differ significantly (t = 0.06, P > 0.1, 1 − β = 0.41), although the small sample size provided limited statistical power. The latter analysis included all the Rat and Delarof islands, and the Andreanof Islands from Great Sitkin westward (n = 23 islands; Table 1) in which ≥20 otters were counted in at least 1 survey period. More recently, we have observed a moderate increase in sea otter population density, with a subsequent decline in energy recovery rates. Dr. Estes suspects that starving orcas — perhaps deprived of their preferred whale prey by industrial whaling — have turned in desperation to the little mammals, which they can gulp down by the hundreds or thousands a year. Lichens live on the side of trees, getting better access to the sun, with no apparent harm to the tree. “These long-lived reefs are disappearing before our eyes,” said Doug Rasher, a marine ecologist at the Bigelow Laboratory for Ocean Sciences in Maine and the study’s first author. Collectively, these efforts chronicle a pattern of population recovery that began in the central Aleutians and gradually spread throughout the archipelago. Therefore our estimate of the magnitude of the decline is conservative. Fur traders in the 18th and 19th centuries hunted the animals to the brink of extinction, allowing sea urchin numbers to skyrocket, Dr. Rasher said. 1) when viewing conditions were good to excellent (Beaufort sea state of 1–2, and >1 km of clear visibility at sea level). The sea otter population was at equilibrial density for several islands in the Rat, Delarof, and western Andreanof islands by 1965 (Kenyon 1969), but numbers declined by 88% by 2000. This represents a 3.6 percent drop for the overall population and an 11 percent drop in the number of otter pups, compared to 2009 estimates. “For their size and how cute they are, they are aggressive eaters.”. Sea otters are an important part of the ocean environment, but their population is declining due to human factors, disease, and killer whales. 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. However, it suggests that the population decline began some time after the mid-1980s. The number of sea otter pups, which represent the future of the species, is down 11 percent. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. Southern sea otter population in decline. 2005. For southern sea otters to be considered for removal from threatened species listing, the overall population estimate would have to exceed 3,090 for three consecutive years. We evaluated the hypothesis that otter densities varied among island groups over time. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Without otters to keep them in check, populations of sea urchins have boomed, carpeting the sea floor in spiny spheres that mow down entire forests of kelp. Otter densities were log-transformed before statistical analyses. “They eat them like popcorn,” Dr. Estes said. Aerial survey counts of sea otters in the Aleutian Islands, Alaska. A massive decline in sea otter populations in the Aleutian Islands accounts for most of the change; the cause of this decline is not known, although orca predation is suspected. Fishery Bulletin 103:270-279. are not readily degraded and do dissolve in fat. Both skiff-based and aerial and counts indicate an annual decline rate of 17% in the west-central archipelago between 1992 and 2000. Population trends.—The general pattern of sea otter recolonization in the Aleutian archipelago through the 1960s was characterized by a slow spread among islands and rapid intraisland population increases after colonization, followed by modest declines and eventual stabilization (Bodkin et al. Remnant colonies of sea otters in the Aleutian archipelago were among the first to recover; they continued to increase through the 1980s but declined abruptly during the 1990s. In recent decades, the sea otter population the Aleutian Islands of western Alaska has plummeted. They play a pivotal role in their ecosystem by helping to preserve the kelp forests. Full Report: California Sea Otter Census Results, Spring 2017 The sea otter population decline in the western Aleutian Islands prompted the United States Fish and Wildlife Service to designate this stock as threatened under the United States Endangered Species Act in 2005. But sharks are only part of the problem. Islands in italics are considered to have been at or near equilibrium density in 1965. 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. As a result, kelp abundance … 1998). “There were so many of them, we couldn’t keep track.”. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. Adak Island in the central Aleutians was studied extensively in the 1990s during the population decline (Estes et al. These colonies subsequently increased to repopulate much of the sea otters' former range. We computed independent rates of population change from skiff-based counts conducted in the western and central Aleutian Islands. Dr. Estes, who is 74, hasn’t visited the Aleutians since 2015. 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. Hence, the eastward extent of the decline apparently occurs somewhere between the Kodiak archipelago and Prince William Sound. Map of the study area denoting 6 major island groups (Near, Rat, Delarof, Andreanof, Four Mountains, and Fox islands) in the Aleutian archipelago. The islands are volcanic in origin, forming a boundary between the Bering Sea and the North Pacific Ocean. 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, … It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. Everywhere the young biologist looked, there were sea otters — lollygagging on kelp beds, shelling sea urchins, exchanging their signature squeals. The reading and the lecture are both about theories of the rapid decline in sea otter populations. 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. 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. It is interesting to note that neither sea otter nor pinniped populations in the Commander Islands, Russia have declined to the degree that they have in the Aleutian archipelago (Bodkin et al. Encounter rates of otters (per km) along transects differed significantly (t = 2.32, P = 0.02) between 1992 (0.04 ± 0.016) and 2000 (0.01 ± 0.004). These data are in general agreement with the hypothesis of increased predation on sea otters. The algae’s decline also seems to be speeding up. Last month the agency released results of its most recent survey, completed in April, which puts the Aleutian population at 6 000 otters, down from a 1980s estimate of 55 000-100 000. Metabolism, driving urchins to eat even more enthusiastically than usual overflights Steiler! 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