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, … "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. The loss is more than cosmetic. “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. Climate change has greatly contributed to this occurrence and the decline in the sea otter population. 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. 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. 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. 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.). We analyze trends in sea otter abundance by comparing the number of animals counted over time and by computing proportional changes between time periods. 1) suggest an increasing population from 1975 to 1994 (Estes 1990; United States Fish and Wildlife Service, in litt. The number of sea otters counted decreased by 75% between 1965 and 2000; 88% for islands at equilibrial density in 1965. The sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. 3a–c) and for those islands that were at or near equilibrial density (noted as K in Figs. Skiff-based surveys at Attu Island (Fig. 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. comm.). All statistical tests were considered to be significant when P < 0.05. Warmer temperatures also speed animal metabolism, driving urchins to eat even more enthusiastically than usual. A. Tinker M. T. Williams T. M. Doak D. F.. Hatfield B. During the past 15–20 years, sea otters Enhydra lutris in the Aleutian Islands, Alaska, USA, experienced a drastic decrease in population size. 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. ; York 1994). The reading and the lecture are both about theories of the rapid decline in sea otter populations. Hence, the eastward extent of the decline apparently occurs somewhere between the Kodiak archipelago and Prince William Sound. It has been hypothesized that an increase in killer whale Orcinus orca predation was the primary cause of this decline.. 2 . As a result, kelp abundance … Differences in aerial and skiff-based population trends were evaluated using a paired t-test. 1978; Kenyon 1969; Lensink 1962). Two or more surveys were conducted in separate years at each of these islands during the 1990s. Hence, the westward extent of the decline appears to be Attu Island. 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. The Alaska Maritime National Wildlife Refuge and the M/V Tiglax provided logistical-support. 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. “They eat them like popcorn,” Dr. Estes said. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. 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. Overflights of Steiler sea lion haulout and rookery sites were permitted under the National Marine Mammal Laboratory's ESA/ MMPA Permit 782-1532-00. We arbitrarily restricted this comparison to islands at which ≥20 otters were counted during at least 1 of the surveys, to avoid spurious results. 2 and 3). 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, … B. In recent decades, the sea otter population the Aleutian Islands of western Alaska has plummeted. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. 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. Map of the study area denoting 6 major island groups (Near, Rat, Delarof, Andreanof, Four Mountains, and Fox islands) in the Aleutian archipelago. 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. 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). 1978), although the data are difficult to interpret because of differing survey methods. The Aleutian archipelago extends westward from Unimak Pass to Attu Island (Fig. The geographic extent of the sea otter population decline is unknown. Collectively, these efforts chronicle a pattern of population recovery that began in the central Aleutians and gradually spread throughout the archipelago. 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. 1998; Hatfield et al. Diverse hypotheses have been advanced to explain the pinniped declines, but their cause (or causes) remains uncertain (National Research Council 1996). Sea otters are an important part of the ocean environment, but their population is declining due to human factors, disease, and killer whales. 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. Both aircraft were equipped with large bubble windows and long-range fuel tanks. He was greeted by an ocean filled with furry faces. 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). “There were so many of them, we couldn’t keep track.”. ESTES ETAL. 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. But met with weakened reef layers, urchins excavated chasms several millimeters deep — the equivalent of up to seven years of growth. The survey crew consisted of a pilot, copilot, 2 observers, and 1 data recorder. 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 further evaluated trends in sea otter abundance by comparing the number of animals counted by island, island group, and across the archipelago, and by computing proportional changes between time periods (Nt2/Nt1). Dr. Estes, who is 74, hasn’t visited the Aleutians since 2015. Aleutian sea otters have been in flux before. However, it suggests that the population decline began some time after the mid-1980s. We evaluated the hypothesis that otter densities varied among island groups over time. The sea otter preys on urchins in Alaska, which allows the kelp forests to thrive as well. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. This is a minimal estimate of abundance because some unknown proportion of the population is not detected in skiff-based surveys (Udevitz et al. We counted sea otters with the unaided eye, using binoculars to confirm sightings or to count animals in large groups. comm.). There are 6 major island groups (Near, Rat, Delarof, Andreanof, Four Mountains, and Fox) that collectively contain 78 major islands with >5,000 km of coastline. In 2000, we resurveyed 35 transects in the western and central Aleutians. 1). Behavior. The mean ratio was then multiplied by the aerial count to obtain a minimal estimate of current population abundance. 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. 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.). Marks D. M. Tinker M. T. Nolan K. Peirce J.. Oxford University Press is a department of the University of Oxford. 3). The information presented in this article chronicles one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. 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). Expected distributions were computed from a lognormal density function with a mean of 1 and the observed variance. 1980; T. Evans et al., in litt.). 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. 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. ; V. Nikulin pers. He doubts he will live to see the otters return. When sea otter populations are healthy, urchin populations are kept in check, and kelp is abundant. 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 hunting of otters by humans has been a major factor. 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). The eastward extent of the decline is less clear. Everywhere the young biologist looked, there were sea otters — lollygagging on kelp beds, shelling sea urchins, exchanging their signature squeals. (ENN) -- Things are not looking good for southern sea otters. 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. Sample sizes are small, but the difference in encounter rates between years is similar to that observed for nearshore aerial surveys. 1994; J. Bodkin et al., in litt.). are not readily degraded and do dissolve in fat. ); it is unclear whether equilibrial density had been reached before the onset of the decline. 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. Observed and expected distributions of proportional change in abundance between selected surveys differed significantly (P < 0.001 in all cases). “Predator loss can impact the environment in ways we haven’t even thought of,” Dr. Griffin said. J. Dunlap provided computer support. 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. All of these increases occurred at islands with small otter populations in 1965. 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. The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. Counts were recorded separately for each section. 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. 1998). 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 indicated trend for any given island may be unreliable due to a small sample size (3 survey periods) and inherent variation in the detection of otters within counts. ; Estes 1990; L. Rotterman and T. Simon-Jackson, in litt. An estimated 6,000 sea otters remain in the Aleutian Islands today. But sharks are only part of the problem. But against the backdrop of climate change, Dr. Rasher said, the reef’s safety net is gone. Results of the spring 1998 southern sea otter survey indicate a 5.2 percent decline in … Full Report: California Sea Otter Census Results, Spring 2017 Population estimates for Amchitka Island in the early 1970s provide no suggestion of a decline (Estes et al. "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. Otter densities were log-transformed before statistical analyses. The southern sea otter population, which once numbered about 16,000 animals, is hovering around 3,000 today. 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). Temporal changes in density of sea otters for major island groups, 1911–2000. 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. 1995). Historically, more than 90 percent of the eagles' food comes from the ocean. 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. Both skiff-based and aerial and counts indicate an annual decline rate of 17% in the west-central archipelago between 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. Data from the 2000 aerial survey indicate that numbers have declined across the entire Aleutian archipelago. By 2000, sea otter densities had declined to a uniformly low level throughout the … 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. That could be a difficult task, given the probable cause of the Aleutian Islands’ stunning vanishing of otters. “For their size and how cute they are, they are aggressive eaters.”. An estimated 6,000 sea otters remain in the Aleutian Islands today. 2005. Dashed lines indicate when no data were available. Estimated dates for the onset of population declines of sea otters at Adak, Amchitka, and Kagalaska islands. 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). United States Fish and Wildlife Service, Marine Mammals Management, 1011 East Tudor Road, Anchorage, AK 99503, USA. These data are in general agreement with the hypothesis of increased predation on sea otters. 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. The decline of the sea otter population in the Pacific Northwest has been attributed to? 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. The sea otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill , which killed thousands of sea otters … In 1970, Jim Estes made his first trek up to Alaska’s Aleutian Islands. 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. Decline in sea otter (Enhydra lutris) populations along the Alaska Peninsula, 1986-2001. The algae’s decline also seems to be speeding up. You wouldn’t think sea otters would affect the climate very much, but their existence keeps other parts of the ecosystem in check. Lichens live on the side of trees, getting better access to the sun, with no apparent harm to the tree. 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. 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). This is an example of? Now, Dr. Estes said, more than 90 percent of those otters are gone. The null hypothesis of no difference between observed and expected distributions was evaluated using a 1-sample K-S test. We evaluated the null hypothesis that there was no difference between observed and expected distributions. Sea otters have not recolonized all former habitats, though their current distribution is considered stable (USFWS 2013b; Ballachey and Bodkin 2015). S. Ashland, B. Elmer, T. Blaesing, and D. Weintraub piloted the surveys. The earliest and most extensive recovery of sea otters after the fur trade occurred in the Aleutian archipelago. ; K. Schneider, in litt.). 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. These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. :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. 1998). 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. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. Skiff-based surveys and related studies were supported by the National Science Foundation and the Department of Defense Legacy Program. 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. 1) when viewing conditions were good to excellent (Beaufort sea state of 1–2, and >1 km of clear visibility at sea level). The number of sea otter pups, which represent the future of the species, is down 11 percent. Cloud cover, Beaufort sea state, wind speed, and visibility conditions were recorded at the beginning of each segment. Kelp provides shelter for sea otters and their pups and a variety of other marine organisms. 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. Multiplying this value by the skiff : aerial correction factor (3.58 ± 0.77; n = 6) provides a population estimate of 8,742 (95% CI = 3,924–13,580) sea otters for the Aleutian Islands 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—. The International Fur Seal Treaty protected the surviving remnant colonies from further harvest beginning in 1911. 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. 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. Sea otters in the Aleutian archipelago have declined substantially in number. “Just seeing that trend is staggering,” Ms. Boyd said. 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. 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. Aerial survey counts of sea otters in the Aleutian Islands, Alaska. Comparison of sea otter population trends based on aerial and skiff-based surveys conducted during the 1990s at 6 islands in the Aleutian archipelago. The minimal population estimate was 8,742 sea otters in 2000. Fishery Bulletin 103:270-279. We computed independent rates of population change from skiff-based counts conducted in the western and central Aleutian Islands. 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. Burn. Emergent trends, however, become more certain when similar counts are summed over multiple islands. 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 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. We conducted an aerial survey of the Aleutian archipelago in 2000 and compared results with similar surveys conducted in 1965 and 1992. 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. 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