To quantify uncertainty for these estimates, we computed 95% confidence interval (CI) for both predecline abundance and trend lines for decline, then calculated intersection points for both trajectories and confidence limits. comm. 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). 3f). 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. Dashed lines indicate when no data were available. Warmer temperatures also speed animal metabolism, driving urchins to eat even more enthusiastically than usual. (ENN) -- Things are not looking good for southern sea otters. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Sea otters in the Aleutian archipelago have declined substantially in number. Nonetheless, the population decline appears to have been relatively recent (Figs. By Environmental News Network staff June 9, 1998 Web posted at: 5:37 PM EDT (1737 GMT) (ENN) -- Things are not looking good for southern sea otters. “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. 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. 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). 1978; Kenyon 1969; Lensink 1962). By the 1950s, sea otter numbers apparently had recovered to pre-commercial harvest levels at some islands in the central Aleutians, although the majority of the archipelago was yet to be re-colonized (Estes 1990; Kenyon 1969). The frequency distributions of the first 3 contrasts (Figs. 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 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. L. Comerci, A. DeGange, S. Kalxdorff, and C. Price were observers during the aerial surveys. 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. However, in southwest Alaska, sea otters have experienced a sharp population decline in the last 20 years. 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. 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. Counts were recorded separately for each section. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. National Research Council 1996). J. Dunlap provided computer support. At Adak Island (the only site with sufficient data for the analysis) the earliest intersection point suggested that population decline began in 1978; however, 7 of the 9 intersection points occurred after 1985. Historically, more than 90 percent of the eagles' food comes from the ocean. The sea otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill , which killed thousands of sea otters … By 2000, sea otter densities had declined to a uniformly low level throughout the archipelago (Fig. 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. The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. Mean encounter rates (otters/km) for the shoreline and transects were compared between 1992 and 2000 surveys. “They eat them like popcorn,” Dr. Estes said. Results of the spring 1998 southern sea otter survey indicate a 5.2 percent decline in … 1980; T. Evans et al., in litt.). Sample sizes are small, but the difference in encounter rates between years is similar to that observed for nearshore aerial surveys. 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. 1994; J. Bodkin et al., in litt.). Where algae had once coated the Aleutian sea floor like a swath of pink pavement, only patches remained. 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). 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. Dr. Estes, who is 74, hasn’t visited the Aleutians since 2015. 2; Table 1). “The reefs are producing less dense skeletons,” Dr. Rasher said. 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. 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. 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. ; York 1994). In 2000, we resurveyed 35 transects in the western and central Aleutians. Otter densities were log-transformed before statistical analyses. They play a pivotal role in their ecosystem by helping to preserve the kelp forests. 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. 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. Temporal changes in density of sea otters for major island groups, 1911–2000. Islands in italics are considered to have been at or near equilibrium density in 1965. 1 . A. Tinker M. T. Williams T. M. Doak D. F.. Hatfield B. 3). A single sea otter can scarf down nearly 1,000 sea urchins a day. Skiff-based surveys and related studies were supported by the National Science Foundation and the Department of Defense Legacy Program. When the oceans had been healthy, the team found, nips from urchins had barely scuffed the algae’s surface. 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. 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. Comparison of sea otter population trends based on aerial and skiff-based surveys conducted during the 1990s at 6 islands in the Aleutian archipelago. In just a few decades, this bustling civilization has withered into a ghost town. Continuing lack of growth in the range peripheries likely explains the cessation of range expansion. 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. It has been hypothesized that an increase in killer whale Orcinus orca predation was the primary cause of this decline.. 2 . “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. The 2016 survey recorded a raw count population size of 3,615, the highest survey result ever. 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. Early European explorers reported vast numbers of sea otters (Enhydra lutris) in coastal waters of the Aleutian archipelago and mainland Alaska (Bancroft 1959; Lensink 1962). 1998). Observed and expected distributions of proportional change in abundance between selected surveys differed significantly (P < 0.001 in all cases). 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. But these hidden relationships might contain hints of remedies. commensalism. We fitted decline trajectories to the survey data using least squares, assuming an exponential function of the form Nt = N0ert. Against the backdrop of climate change, the delicate underwater ecology of Alaska’s Aleutian Islands is hurting from declines in otters. Sea otters are an important part of the ocean environment, but their population is declining due to human factors, disease, and killer whales. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. All statistical tests were considered to be significant when P < 0.05. 2 and 3). More recently, we have observed a moderate increase in sea otter population density, with a subsequent decline in energy recovery rates. Everywhere the young biologist looked, there were sea otters — lollygagging on kelp beds, shelling sea urchins, exchanging their signature squeals. 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. He was greeted by an ocean filled with furry faces. Aerial surveys.—We conducted aerial surveys from 1–30 April 1992 and 11–29 April 2000. When sea otter populations are healthy, urchin populations are kept in check, and kelp is abundant. The minimal population estimate was 8,742 sea otters in 2000. Observers sat aft of the pilots on each side of the plane. 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. We evaluated the null hypothesis that there was no difference between observed and expected distributions. An estimated 6,000 sea otters remain in the Aleutian Islands today. 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). The number of sea otter pups, which represent the future of the species, is down 11 percent. Skiff-based surveys at Attu Island (Fig. 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 International Fur Seal Treaty protected the surviving remnant colonies from further harvest beginning in 1911. The Alaska Maritime National Wildlife Refuge and the M/V Tiglax provided logistical-support. B. The spring 1999 survey of 2,090 California sea otters indicates the population has declined overall by 1.14 percent since the 1998 spring survey, which revealed that there were a total of 2,114. ESTES ETAL. “Just seeing that trend is staggering,” Ms. Boyd said. The survey crew consisted of a pilot, copilot, 2 observers, and 1 data recorder. Hence, the westward extent of the decline appears to be Attu Island. This indicates that the population may be reaching its carrying capacity for this region (Figures 1 and 2). The decline of the sea otter population in the Pacific Northwest has been attributed to? 2000; A. M. Burdin, pers. 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. Aerial surveys have many limitations but provide the only practical means of rapid and complete coverage of sea otter habitat over a vast and remote region. All statistics are reported ± 1 SE, unless otherwise indicated. Climate change has greatly contributed to this occurrence and the decline in the sea otter population. 1995). Differences in aerial and skiff-based population trends were evaluated using a paired t-test. 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. Although the California sea otter population is declining, the geographic range of the population continues to expand both to the north and south. Cloud cover, Beaufort sea state, wind speed, and visibility conditions were recorded at the beginning of each segment. 1) when viewing conditions were good to excellent (Beaufort sea state of 1–2, and >1 km of clear visibility at sea level). Fishery Bulletin 103:270-279. 3a–c) and for those islands that were at or near equilibrial density (noted as K in Figs. Decline in sea otter (Enhydra lutris) populations along the Alaska Peninsula, 1986-2001. We computed independent rates of population change from skiff-based counts conducted in the western and central Aleutian Islands. 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. That could make it hard to sustain larger otter populations: Once introduced, they might just disappear all over again. 2005. 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.”. Therefore our estimate of the magnitude of the decline is conservative. 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. "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. When otter populations recovered after trapping was restricted, the reef rebounded, too. Expected distributions were computed from a lognormal density function with a mean of 1 and the observed variance. Aerial survey counts of sea otters in the Aleutian Islands, Alaska. Alaskan reefs, built by the coralline algae C. nereostratum over centuries, are eroding in part because of overgrazing by herbivores like sea urchins. The eastward extent of the decline is less clear. 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 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). 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). 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. In contrast, Dr. Estes noticed that places with healthy sea otter populations often had healthy kelp forest habitat as well. “And temperature exacerbates that issue.”. 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. 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. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. Behavior. 3a–c) were distinctly bimodal, indicating that, although otter numbers at most islands were in decline during this period, they increased markedly at others. Against the backdrop of climate change, the delicate underwater ecology of Alaska’s Aleutian Islands is hurting from declines in otters. We arbitrarily restricted this comparison to islands at which ≥20 otters were counted during at least 1 of the surveys, to avoid spurious results. 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. 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. A.. Estes J. These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. These data chronicle one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. Full Report: California Sea Otter Census Results, Spring 2017 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. Burn. Adak Island in the central Aleutians was studied extensively in the 1990s during the population decline (Estes et al. But against the backdrop of climate change, Dr. Rasher said, the reef’s safety net is gone. Mean annual rates of decline were not significantly different (t = 0.06, P > 0.05). 1) suggest an increasing population from 1975 to 1994 (Estes 1990; United States Fish and Wildlife Service, in litt. Continuing sea otter population declines in the Aleutian archipelago. This analysis was done separately for aerial survey data from 1965, 1992, and 2000. 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. 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. 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. "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. 2000; E. Mamaev, pers. We analyze trends in sea otter abundance by comparing the number of animals counted over time and by computing proportional changes between time periods. Tinker, A.M. Doroff, and D.M. 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. In the Aleutians’ delicate seascape, otters hold the entire ecosystem together. In 1992, the survey aircraft was a deHavilland turbine Twin Otter, and in 2000 the survey aircraft was a turbine Aero Commander 690A. 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. 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. “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. We evaluated the hypothesis that otter densities varied among island groups over time. 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. 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. Now, even the living, red-algae reefs on which the swirling stands of kelp once stood are in peril. “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. 1998). Analytical methods.—We established early trends of sea otter abundance and distribution in the Aleutian archipelago from historical records provided by Kenyon (1969). These data are in general agreement with the hypothesis of increased predation on sea otters. Location, altitude, weather, visibility, and observer identification were recorded directly into an onboard computer interfaced with a global positioning system. 2). For many years, there were no sea otters in Canadian waters and most of the sea otters in the world were … Transects were digitized for the entire archipelago and of these, 61 were randomly sampled in 1992. Encounter rates of sea otters for each island were obtained by dividing the uncorrected counts by the length of shoreline surveyed (hereafter these measures are referred to as densities). 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. 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. 2–4) but well underway by 1992 (Table 1; Figs. These trajectories were then hindcast to when they intersected predecline estimates of abundance. 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. The islands are volcanic in origin, forming a boundary between the Bering Sea and the North Pacific Ocean. We dedicate the aerial survey work to T. Blaesing, whose creativity and skill facilitated the collection of complete data of high quality. The severity and geographic extent of this decline raise several conservation concerns. Current population size.—We counted 2,442 sea otters in the aerial survey of spring 2000. comm.). 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, … The latest count of this threatened species shows their population dropped to just 2,711, a decline of 3.6 percent. Many individuals assisted with the skiff-based surveys throughout the 1990s, including D. Irons, J. Meehan, D. Monson, and J. Stewart. 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. Kelp provides shelter for sea otters and their pups and a variety of other marine organisms. 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. 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. Population estimates for Amchitka Island in the early 1970s provide no suggestion of a decline (Estes et al. This is a minimal estimate of abundance because some unknown proportion of the population is not detected in skiff-based surveys (Udevitz et al. Data from the 2000 aerial survey indicate that numbers have declined across the entire Aleutian archipelago. 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