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. 2; Table 1). In 2001, the US Fish and Wildlife Service (USFWS) designated the Aleutian Islands population of northern sea otter as a candidate species for listing under the Endangered Species Act (ESA). 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. Because sea otter counts obtained from aerial surveys are biased low (Bodkin and Udevitz 1999; Kenyon 1969; Lensink 1962), we estimated a minimal correction factor for the 2000 aerial survey by computing the mean ratio of the skiff : aerial counts for the 6 islands surveyed in 2000. 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. Kelp provides shelter for sea otters and their pups and a variety of other marine organisms. Sample sizes are small, but the difference in encounter rates between years is similar to that observed for nearshore aerial surveys. 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. The minimal population estimate was 8,742 sea otters in 2000. All statistics are reported ± 1 SE, unless otherwise indicated. Back then, crowds of these charismatic creatures shrouded the sprawling archipelago, congregating in “rafts and bunches, as many as 500 at once,” said Dr. Estes, an ecologist at the University of California, Santa Cruz. In the Aleutians’ delicate seascape, otters hold the entire ecosystem together. All statistical tests were considered to be significant when P < 0.05. The sea otter preys on urchins in Alaska, which allows the kelp forests to thrive as well. (pdf) Estes, J.A., M.T. Now, Dr. Estes said, more than 90 percent of those otters are gone. The International Fur Seal Treaty protected the surviving remnant colonies from further harvest beginning in 1911. 1 . ; Estes 1990; L. Rotterman and T. Simon-Jackson, in litt. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. 3a–c) and for those islands that were at or near equilibrial density (noted as K in Figs. “Ocean warming and acidification are making it difficult for calcifying organisms to produce their shells, or in this case, the alga’s protective skeleton,” said Rasher. 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). We evaluated the null hypothesis that there was no difference between observed and expected distributions. The loss is more than cosmetic. To quantify the damage, Dr. Rasher and his colleagues braved high winds and freezing waters to collect samples over several years of the dwindling algae and analyzed them in the lab. Against the backdrop of climate change, the delicate underwater ecology of Alaska’s Aleutian Islands is hurting from declines in otters. 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 met with weakened reef layers, urchins excavated chasms several millimeters deep — the equivalent of up to seven years of growth. The hunting of otters by humans has been a major factor. Counts were recorded separately for each section. 1980; T. Evans et al., in litt.). In the 1980s, the area was home to an estimated 55,000 to 100,000 sea otters, but the population fell to around 6,000 animals by 2000. Sea otters, … “The reefs are producing less dense skeletons,” Dr. Rasher said. Systematic aerial surveys of sea otters in the Aleutian Islands were initiated in 1957 (Kenyon 1969) in conjunction with site-specific surveys that employed a variety of techniques (Estes et al. Decline in Sea Otter Population Foley Ms. Hall 2nd Period Biology This picture was taken by student Sara Rappl, of an otter in an enclosure. We surveyed the shoreline of each island in its entirety. comm. "A 1 percent decline does not seem like much, but we now have fewer otters than in 1993, and there has apparently been an 11 percent decline since the population peaked in 1995," Shimek said. We computed independent rates of population change from skiff-based counts conducted in the western and central Aleutian Islands. The algae’s decline also seems to be speeding up. 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. 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. 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. 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. The more detailed results of skiff-based surveys conducted at several islands during the 1990s are used to define decline trajectories more precisely and provide a minimal estimate of bias in the aerial counts. These data are in general agreement with the hypothesis of increased predation on sea otters. They play a pivotal role in their ecosystem by helping to preserve the kelp forests. Current population size.—We counted 2,442 sea otters in the aerial survey of spring 2000. Kiska and Little Kiska include Pyramid Island; Great Sitkin includes Ulak, Aziak, Tanaklak, Kanu, Asuksak, and Tagadak islands; Atka includes Segchudak, Sadatanak, Amtagis, and Salt islands; Umnak and Samalga include Bogoslof, Vsevidof, Ogchul, Kigul, and Adugak islands. Repatriating otters could help reefs in the near-term, Dr. Rasher said, perhaps “buying us time to get our act together in terms of curbing global carbon emissions.”. (ENN) -- Things are not looking good for southern sea otters. 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. “The amount of things they control in this ecosystem is pretty astonishing,” said Anjali Boyd, a marine ecologist at Duke University who wasn’t involved in the study. Elevated adult mortality was found to be the primary cause of the population decline, and predation by killer whales (Orcinus orcd) is thought to be the principal reason for this mortality (Estes et al. We also compared mean annual rates of decline as estimated by skiffbased and aerial surveys of all islands (15.0%/year (±1.74; n = 29)) but did not detect a difference (t = 0.857, P > 0.1, 1 − β = 0.47). By the 1980s, an estimated 55,000–74,000 animals inhabited the archipelago, and continued population growth was expected (D. Calkins and K. Schneider, in litt. Southern sea otter population in decline. 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. This analysis was done separately for aerial survey data from 1965, 1992, and 2000. For southern sea otters to be considered for removal from threatened species listing, the population index would have to exceed 3,090 for three consecutive years, according to the threshold established under the Southern Sea Otter Recovery Plan by the U.S. Sea otters are an important part of the ocean environment, but their population is declining due to human factors, disease, and killer whales. 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. 1) suggest an increasing population from 1975 to 1994 (Estes 1990; United States Fish and Wildlife Service, in litt. 3a–c) were distinctly bimodal, indicating that, although otter numbers at most islands were in decline during this period, they increased markedly at others. The 2017 USGS southern sea otter survey results showed the raw count population size dropped to 2,688 an over 25 percent decline from last year. ); it is unclear whether equilibrial density had been reached before the onset of the decline. 1998). Remnant populations, located in the central Aleutian Islands, were monitored infrequently through the 1950s (Kenyon 1969; Lensink 1962; Murie 1959). When the researchers grew urchins and algae under conditions that simulated the preindustrial past, the present and a projected future in the lab, they found that contemporary circumstances spurred urchins to gnaw away at algae up to 60 percent faster. Sea otters had spread to all island groups by 1992, but the overall count at that time had declined by approximately 50% in the central Aleutians since the 1965 survey (T. Evans et al., in litt.). Adak Island in the central Aleutians was studied extensively in the 1990s during the population decline (Estes et al. Fishery Bulletin 103:270-279. Hence, the westward extent of the decline appears to be Attu Island. Continuing lack of growth in the range peripheries likely explains the cessation of range expansion. 1978), although the data are difficult to interpret because of differing survey methods. Sea otters spend much of their lives in the water and can dive up to 330 feet when foraging for food, though most dives are much shallower. Burn. For three consecutive years from 2016 through 2018, the average southern sea otter population, which includes those found in Monterey Bay, narrowly topped the … To avoid the unknown and potentially confounding effects of range expansion and population growth between 1965 and 1992, we repeated the analysis for those islands that Kenyon (1969) assumed to be at or near equilibrial density in 1965 (defined here as that which occurred when populations ceased growing because of resource limitation). Location, altitude, weather, visibility, and observer identification were recorded directly into an onboard computer interfaced with a global positioning system. This is arguably the case for all large terrestrial carnivores (Diamond 1984), including various species of wolves, bears, and large cats throughout the world, although in most cases the declines are poorly chronicled. Skiff-based surveys and related studies were supported by the National Science Foundation and the Department of Defense Legacy Program. Against the backdrop of climate change, the delicate underwater ecology of Alaska’s Aleutian Islands is hurting from declines in otters. Estimated dates for the onset of population declines of sea otters at Adak, Amchitka, and Kagalaska islands. However, recent surveys of sea otters in the Commander Islands, Russia (approximately 300 km west of Attu Island) suggest a stable population there since 1992 (Bodkin et al. Behavior. more than 90 percent of those otters are gone, acidified ocean waters, making it harder for algae to armor themselves. Now, even the living, red-algae reefs on which the swirling stands of kelp once stood are in peril. 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. Continuing sea otter population declines in the Aleutian archipelago. “You can travel down 10 miles of coastline and never see an animal,” he said. United States Fish and Wildlife Service, Marine Mammals Management, 1011 East Tudor Road, Anchorage, AK 99503, USA. 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. “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. 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. 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. Observers sat aft of the pilots on each side of the plane. S. Ashland, B. Elmer, T. Blaesing, and D. Weintraub piloted the surveys. Viewing conditions were good to excellent during both surveys with approximately 90% of sightings made in average wind speeds of ≤19 km/h. Sea otters once also occupied a large range of coastal marine environments near … The sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. The severity and geographic extent of this decline raise several conservation concerns. “There were so many of them, we couldn’t keep track.”. An estimated 6,000 sea otters remain in the Aleutian Islands today. Climate change has greatly contributed to this occurrence and the decline in the sea otter population. Historically, more than 90 percent of the eagles' food comes from the ocean. 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. The 5-year average trend in abundance, including both the mainland range and San Nicolas Island populations, remains positive at 2.3 percent per year. 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). 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. Dashed lines indicate when no data were available. are not readily degraded and do dissolve in fat. 1998). Transects were digitized for the entire archipelago and of these, 61 were randomly sampled in 1992. Non-significant results are accompanied by a report of statistical power (1 − β), where β is the probability of making a type-II error. ; York 1994). He doubts he will live to see the otters return. The earliest and most extensive recovery of sea otters after the fur trade occurred in the Aleutian archipelago. ; K. Schneider, in litt.). 2). 1). 1978; L. Rotterman and T. Simon-Jackson, in litt.). This is a minimal estimate of abundance because some unknown proportion of the population is not detected in skiff-based surveys (Udevitz et al. 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.). Mean encounter rates (otters/km) for the shoreline and transects were compared between 1992 and 2000 surveys. 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. The sea otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill , which killed thousands of sea otters … We dedicate the aerial survey work to T. Blaesing, whose creativity and skill facilitated the collection of complete data of high quality. Marks D. M. Tinker M. T. Nolan K. Peirce J.. Oxford University Press is a department of the University of Oxford. It has been hypothesized that an increase in killer whale Orcinus orca predation was the primary cause of this decline.. 2 . comm.). But he holds out hope that the islands will someday boomerang back to the breathtaking ecosystem he witnessed as a young man. It’s one reason for a worrying decline in the number of California sea otters. “And temperature exacerbates that issue.”. 2005. Many questions about the geographic extent and ultimate cause of the sea otter decline in southwestern Alaska remain, but our findings demonstrate that once-abundant populations have collapsed across the entire Aleutian archipelago. Aerial surveys were funded by the United States Fish and Wildlife Service, United States Geological Survey, and United States Navy. The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. We fitted decline trajectories to the survey data using least squares, assuming an exponential function of the form Nt = N0ert. Warmer temperatures also speed animal metabolism, driving urchins to eat even more enthusiastically than usual. “For their size and how cute they are, they are aggressive eaters.”. The southern sea otter population, which once numbered about 16,000 animals, is hovering around 3,000 today. The minimal population estimate was 8,742 sea otters in 2000. Onset of decline.—To estimate when population declines began in the Aleutian Islands, we first computed trajectories in counts at those islands where ≥3 skiff-based surveys were conducted in the 1990s (Adak, Amchitka, and Kagalaska islands). “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. Map of the study area denoting 6 major island groups (Near, Rat, Delarof, Andreanof, Four Mountains, and Fox islands) in the Aleutian archipelago. 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). ESTES ETAL. The shoreline of each island was divided into contiguous segments, each 3–10 km in length and separated by distinctive topographic features (e.g., prominent points of land). 1) when viewing conditions were good to excellent (Beaufort sea state of 1–2, and >1 km of clear visibility at sea level). "A 1 percent decline does not seem like much, but we now have fewer otters than in 1993, and there has apparently been an 11 percent decline since the population peaked in 1995," Shimek said. Many other carnivorous mammals have been lost from large segments of their historical range, but in nearly all instances the populations dwindled more gradually because of direct human exploitation, predator control, poaching, and habitat destruction. “It was spectacularly beautiful.”, When the Otters Vanished, Everything Else Started to Crumble. We present general patterns of population change for sea otters in the Aleutian Islands through compilation of aerial survey data from the late 1950s to 2000. Thus, the 3 surveys (1965, 1992, and 2000) provide a reasonable assessment of gross change in distribution and relative abundance of sea otters in the Aleutian archipelago over a 35-year period (Fig. The southern sea otter, also called the California sea otter, is a smaller subspecies genetically different from its northern neighbor. 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. A. Tinker M. T. Williams T. M. Doak D. F.. Hatfield B. The frequency distributions of the first 3 contrasts (Figs. 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). We counted sea otters with the unaided eye, using binoculars to confirm sightings or to count animals in large groups. 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. We evaluated the hypothesis that otter densities varied among island groups over time. The survey crew consisted of a pilot, copilot, 2 observers, and 1 data recorder. Although the urchins eagerly descended upon the local smorgasbord of kelp, the bubblegum-pink reef beneath them seems to have persisted — in part because healthy algae produce a protective limestone layer that can thwart even the most determined grazers. We also compared the distribution of annual rates of decline for the 6 islands surveyed by skiff with that for the entire archipelago, based on 1992 and 2000 aerial surveys. The null hypothesis of no difference between observed and expected distributions was evaluated using a 1-sample K-S test. Dr. Estes, who is 74, hasn’t visited the Aleutians since 2015. The sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. There were no clear patterns to the distributions of the residual values, indicating that the exponential decay function was appropriate for describing the observed trends. Sea otters once also occupied a large range of coastal marine environments near these islands, but in recent years, otter populations have declined in response to their own main predator. Emergent trends, however, become more certain when similar counts are summed over multiple islands. However, this did not prevent the sea otter population from continuing to decline, and in 1929, the last verified sea otter in Canada was shot and killed (Nichol, 2002). :SEA OTTER MORTALITY 199 of growth and decline included a decrease in per capita pup production and massilength ratios of adult carcasses over the 31-yr study. 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. However, in southwest Alaska, sea otters have experienced a sharp population decline in the last 20 years. 1995). The Alaska Maritime National Wildlife Refuge and the M/V Tiglax provided logistical-support. When otter populations recovered after trapping was restricted, the reef rebounded, too. However, it suggests that the population decline began some time after the mid-1980s. We surveyed all major islands and offshore rocks of the Aleutian archipelago except for Chagulak Island in the Islands of Four Mountains, which was omitted because of the high risk associated with flying near its large seabird colony. L. Comerci, A. DeGange, S. Kalxdorff, and C. Price were observers during the aerial surveys. Angela M. Doroff, James A. Estes, M. Tim Tinker, Douglas M. Burn, Thomas J. Evans, Sea Otter Population Declines in the Aleutian Archipelago, Journal of Mammalogy, Volume 84, Issue 1, 28 February 2003, Pages 55–64, https://doi.org/10.1644/1545-1542(2003)084<0055:SOPDIT>2.0.CO;2. 2 and 3). In 2000, we resurveyed 35 transects in the western and central Aleutians. 2000; E. Mamaev, pers. Otter densities were log-transformed before statistical analyses. In 1970, Jim Estes made his first trek up to Alaska’s Aleutian Islands. Many individuals assisted with the skiff-based surveys throughout the 1990s, including D. Irons, J. Meehan, D. Monson, and J. Stewart. Current status of populations in Lower Cook Inlet and the Kenai Peninsula is unknown; however, annual surveys in Prince William Sound show no indication of a decline, despite extensive impacts from the Exxon Valdez oil spill (Ballachey et al. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. In California, sea otter abundance has failed to reach conservation goals, and for many decades growth rates have been lower than expected, relative to other remnant populations (Bodkin et al., 1999), with periods of modest growth and decline despite focused efforts to protect sea otters and measures to enhance population growth. Everywhere the young biologist looked, there were sea otters — lollygagging on kelp beds, shelling sea urchins, exchanging their signature squeals. The geographic extent of the sea otter population decline is unknown. From 2014 through 2017, some reefs shrank by up to 64 percent. As a result, kelp abundance … Data from the 2000 aerial survey indicate that numbers have declined across the entire Aleutian archipelago. comm.). When sea otter populations are healthy, urchin populations are kept in check, and kelp is abundant. 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. To avoid spurious results, we arbitrarily restricted the latter analyses to islands where 20 or more otters were counted during at least 1 aerial survey. 1998). 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. Representative densities for each period were based on maximal counts by aircraft for each island divided by the length of shoreline surveyed for each group. Extensive hunting of these animals for their valuable pelts eliminated the species from most of its historic range, which extended across the Pacific Rim from Japan to the Pacific coast of Mexico (Kenyon 1969; Lensink 1962; Reidman and Estes 1990; L. Rotterman and T Simon-Jackson, in litt.). Decline in sea otter (Enhydra lutris) populations along the Alaska Peninsula, 1986-2001. National Research Council 1996). 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. Results of the spring 1998 southern sea otter survey indicate a 5.2 percent decline in … By 2000, sea otter densities had declined to a uniformly low level throughout the … The findings add yet another example to the list of ecosystems being ravaged by an ever-warming world, and underscore how food chain alterations and climate change can disastrously collide. 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Function of the eagles ' food comes from the 2000 aerial survey indicate that have! This threatened species shows their population dropped to just 2,711, a decline in the Pacific has! Boomerang back to the tree “ just seeing that trend is staggering, ” Dr. Rasher,. This region ( Figures 1 and the Department of Defense Legacy Program population size.—We counted 2,442 sea otters repopulated. Data chronicle one of the decline is conservative, we have observed a moderate in... All statistics are reported ± 1 SE, unless otherwise indicated a result, kelp abundance … it s! Appears to be significant when P < 0.001 in all cases ) and indicate!
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