Climate change has greatly contributed to this occurrence and the decline in the sea otter population. Otter densities were log-transformed before statistical analyses. 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. But against the backdrop of climate change, Dr. Rasher said, the reef’s safety net is gone. Continuing sea otter population declines in the Aleutian archipelago. 3). 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. You wouldn’t think sea otters would affect the climate very much, but their existence keeps other parts of the ecosystem in check. Nonetheless, the population decline appears to have been relatively recent (Figs. This analysis was done separately for aerial survey data from 1965, 1992, and 2000. 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. 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. We analyze trends in sea otter abundance by comparing the number of animals counted over time and by computing proportional changes between time periods. The algae’s decline also seems to be speeding up. 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. commensalism. “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. 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. By 2000, sea otter densities had declined to a uniformly low level throughout the … Population estimates for Amchitka Island in the early 1970s provide no suggestion of a decline (Estes et al. 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. 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. The uniformly low density to which sea otter populations have declined across the Aleutian archipelago suggests that factors contributing to the population decline may be density-dependent. 1978), although the data are difficult to interpret because of differing survey methods. Diverse hypotheses have been advanced to explain the pinniped declines, but their cause (or causes) remains uncertain (National Research Council 1996). Although the California sea otter population is declining, the geographic range of the population continues to expand both to the north and south. Mean encounter rates (otters/km) for the shoreline and transects were compared between 1992 and 2000 surveys. 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. When combined with aerial survey data from 1965, 1992, and 2000, these records are sufficient to chronicle broad patterns of population change across the 6 main island groups. Now, even the living, red-algae reefs on which the swirling stands of kelp once stood are in peril. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. 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. Differences in aerial and skiff-based population trends were evaluated using a paired t-test. He was greeted by an ocean filled with furry faces. The Aleutian archipelago extends westward from Unimak Pass to Attu Island (Fig. 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). Skiff-based surveys at Attu Island (Fig. A.. Estes J. Aerial surveys were funded by the United States Fish and Wildlife Service, United States Geological Survey, and United States Navy. "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. Comparison of sea otter population trends based on aerial and skiff-based surveys conducted during the 1990s at 6 islands in the Aleutian archipelago. :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. 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. We arbitrarily restricted this comparison to islands at which ≥20 otters were counted during at least 1 of the surveys, to avoid spurious results. ESTES ETAL. 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. Data from the 2000 aerial survey indicate that numbers have declined across the entire Aleutian archipelago. 1). The loss is more than cosmetic. “There was this incredible diversity,” he said. 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. Southern sea otter population in decline. The number of sea otter pups, which represent the future of the species, is down 11 percent. 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. 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. 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. Overflights of Steiler sea lion haulout and rookery sites were permitted under the National Marine Mammal Laboratory's ESA/ MMPA Permit 782-1532-00. 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). “You can travel down 10 miles of coastline and never see an animal,” he said. “Just seeing that trend is staggering,” Ms. Boyd said. 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. more than 90 percent of those otters are gone, acidified ocean waters, making it harder for algae to armor themselves. 1998). 2; Table 1). From 2014 through 2017, some reefs shrank by up to 64 percent. However, in southwest Alaska, sea otters have experienced a sharp population decline in the last 20 years. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. 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). The sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. 2000; E. Mamaev, pers. 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. The sea otter preys on urchins in Alaska, which allows the kelp forests to thrive as well. 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.). Both aircraft were equipped with large bubble windows and long-range fuel tanks. Sea otter (Enhydra lutris) populations were exploited to near extinction and began to recover after the cessation of commercial hunting in 1911. Hence, the westward extent of the decline appears to be Attu Island. 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. Mean annual rates of decline were not significantly different (t = 0.06, P > 0.05). The eastward extent of the decline is less clear. “The reefs are producing less dense skeletons,” Dr. Rasher said. Analytical methods.—We established early trends of sea otter abundance and distribution in the Aleutian archipelago from historical records provided by Kenyon (1969). 1998). Emergent trends, however, become more certain when similar counts are summed over multiple islands. "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. 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. 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. 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. Search for other works by this author on: Long Marine Laboratory, Biology Department and Institute of Marine Sciences, United States Geological Survey, University of California, Santa Cruz, CA 95004, USA, Age and sex-specific mortality and population structure in sea otters, An aerial survey method to estimate sea otter abundance, Marine mammal survey and assessment methods, Estimation of density from line transect sampling of biological populations, Statistical power analysis for the behavioral sciences, Historic extinctions: a rosetta stone for understanding prehistoric extinctions, Growth and equilibrium in sea otter populations, Sea otter predation and community organization in the western Aleutian Islands, Alaska, Killer whale predation on sea otters linking oceanic and near shore ecosystems, The sea otter in the eastern Pacific Ocean, The history and status of sea otters in Alaska, Fauna of the Aleutian Islands and Alaska Peninsula, United States Fish and Wildlife Service Biological Report, Detection of sea otters in boat-based surveys of Prince William Sound, Alaska, The population dynamics of Northern sea lions, 1975-1985, Innovations that changed Mammalogy: field fixation for transmission electron microscopy (TEM), Local trends in abundance of migratory bats across 20 years, Landscape-wide flight activity by wintering bats predictably follows pulses of warmth in the Midwestern United States, About the American Society of Mammalogists, https://doi.org/10.1644/1545-1542(2003)084<0055:SOPDIT>2.0.CO;2, Receive exclusive offers and updates from Oxford Academic, Copyright © 2021 American Society of Mammalogists. Collectively, these efforts chronicle a pattern of population recovery that began in the central Aleutians and gradually spread throughout the archipelago. The 2016 survey recorded a raw count population size of 3,615, the highest survey result ever. Killer whales presumably shifted their diet to include sea otters after populations of their preferred prey, harbor seals (Phoca vitulina) and Steiler sea lions (Eumetopias jubatus), declined. The survey crew consisted of a pilot, copilot, 2 observers, and 1 data recorder. 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 … 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. Therefore our estimate of the magnitude of the decline is conservative. Now, Dr. Estes said, more than 90 percent of those otters are gone. Clearly the world has long recognized the need and use of these beautiful creatures, as the first treaty to protect them was signed almost 100 years ago, and they have been included in almost every major animal protection statute since then. National Research Council 1996). 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. Adak Island in the central Aleutians was studied extensively in the 1990s during the population decline (Estes et al. 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. The minimal population estimate was 8,742 sea otters in 2000. Current population size.—We counted 2,442 sea otters in the aerial survey of spring 2000. 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. Kelp provides shelter for sea otters and their pups and a variety of other marine organisms. 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. 2019). An estimated 6,000 sea otters remain in the Aleutian Islands today. Aleutian sea otters have been in flux before. ; Estes 1990; L. Rotterman and T. Simon-Jackson, in litt. 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. The sea otter declines, which appear to differ from their terrestrial counterparts in both pattern and apparent cause, are remarkable because they occurred immediately after abrupt population declines in 3 broadly sympatric species of pinniped (northern fur seals Callhorinus ursinus, Steller sea lion E. jubatus, and harbor seals P. vitulina—. 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. In the Aleutians’ delicate seascape, otters hold the entire ecosystem together. Cloud cover, Beaufort sea state, wind speed, and visibility conditions were recorded at the beginning of each segment. comm.). Expected distributions were computed from a lognormal density function with a mean of 1 and the observed variance. 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. Continuing lack of growth in the range peripheries likely explains the cessation of range expansion. “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 surveys in 2000 and 2001 of the Alaska Peninsula and Kodiak archipelago indicate significant declines in those areas (United States Fish and Wildlife Service, in litt.). These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. 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. 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). 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). Transects were digitized for the entire archipelago and of these, 61 were randomly sampled in 1992. Although the population of sea otters continues to decline worldwide there is hope that they will one day return to their former glory in the animal kingdom. Sea otters, … Sea otters are an important part of the ocean environment, but their population is declining due to human factors, disease, and killer whales. In recent decades, the sea otter population the Aleutian Islands of western Alaska has plummeted. 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). J. Dunlap provided computer support. 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. 2). Sample sizes are small, but the difference in encounter rates between years is similar to that observed for nearshore aerial surveys. Where algae had once coated the Aleutian sea floor like a swath of pink pavement, only patches remained. The decline of the sea otter population in the Pacific Northwest has been attributed to? The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. 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. Sea otters once also occupied a large range of coastal marine environments near … But he holds out hope that the islands will someday boomerang back to the breathtaking ecosystem he witnessed as a young man. 3a–c) were distinctly bimodal, indicating that, although otter numbers at most islands were in decline during this period, they increased markedly at others. 1995). Both skiff-based and aerial and counts indicate an annual decline rate of 17% in the west-central archipelago between 1992 and 2000. For many years, there were no sea otters in Canadian waters and most of the sea otters in the world were … All statistical tests were considered to be significant when P < 0.05. 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). Warmer temperatures also speed animal metabolism, driving urchins to eat even more enthusiastically than usual. We dedicate the aerial survey work to T. Blaesing, whose creativity and skill facilitated the collection of complete data of high quality. But these hidden relationships might contain hints of remedies. 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. When sea otter populations are healthy, urchin populations are kept in check, and kelp is abundant. 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 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.). 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. 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. 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.”. 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). 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. Sea otters in the Aleutian archipelago have declined substantially in number. Estimated dates for the onset of population declines of sea otters at Adak, Amchitka, and Kagalaska islands. When otter populations recovered after trapping was restricted, the reef rebounded, too. 1978; Kenyon 1969; Lensink 1962). These data are in general agreement with the hypothesis of increased predation on sea otters. 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). ; K. Schneider, in litt.). (ENN) -- Things are not looking good for southern sea otters. ; York 1994). B. Ballachey B. E. Bodkin J. L. Degange A. R.. Bodkin J. L. Burdin A. M. Ryazanov D. A.. Burnham K. P. Anderson D. R. Laake J. That could be a difficult task, given the probable cause of the Aleutian Islands’ stunning vanishing of otters. Counts were recorded separately for each section. We conducted an aerial survey of the Aleutian archipelago in 2000 and compared results with similar surveys conducted in 1965 and 1992. Observers sat aft of the pilots on each side of the plane. Temporal changes in density of sea otters for major island groups, 1911–2000. Dr. Estes, who is 74, hasn’t visited the Aleutians since 2015. Remnant populations, located in the central Aleutian Islands, were monitored infrequently through the 1950s (Kenyon 1969; Lensink 1962; Murie 1959). 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. The geographic extent of the sea otter population decline is unknown. Many individuals assisted with the skiff-based surveys throughout the 1990s, including D. Irons, J. Meehan, D. Monson, and J. Stewart. “There were so many of them, we couldn’t keep track.”. The Alaska Maritime National Wildlife Refuge and the M/V Tiglax provided logistical-support. 1 . 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. Hence, the eastward extent of the decline apparently occurs somewhere between the Kodiak archipelago and Prince William Sound. All statistics are reported ± 1 SE, unless otherwise indicated. 1998). We sampled offshore habitat by surveying line transects that were perpendicular to the shoreline and extended to the 50-fathom (91.4 m) isobath (Burnham et al. A single sea otter can scarf down nearly 1,000 sea urchins a day. Historically, more than 90 percent of the eagles' food comes from the ocean. 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