“There were so many of them, we couldn’t keep track.”. 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.). 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. 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.). “Just seeing that trend is staggering,” Ms. Boyd said. 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. 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 sea otter preys on urchins in Alaska, which allows the kelp forests to thrive as well. ; K. Schneider, in litt.). J. Dunlap provided computer support. ESTES ETAL. As a result, kelp abundance … We fitted decline trajectories to the survey data using least squares, assuming an exponential function of the form Nt = N0ert. Southern sea otter population in decline. Skiff-based surveys at Attu Island (Fig. 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. "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. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. 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.”. 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. 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. 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. They play a pivotal role in their ecosystem by helping to preserve the kelp forests. “Predator loss can impact the environment in ways we haven’t even thought of,” Dr. Griffin said. These data chronicle one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. 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. Both skiff-based and aerial and counts indicate an annual decline rate of 17% in the west-central archipelago between 1992 and 2000. Both aircraft were equipped with large bubble windows and long-range fuel tanks. Fishery Bulletin 103:270-279. 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. Two or more surveys were conducted in separate years at each of these islands during the 1990s. But met with weakened reef layers, urchins excavated chasms several millimeters deep — the equivalent of up to seven years of growth. Sea otters are an important component of the ocean environment. 1994; J. Bodkin et al., in litt.). Sea otter (Enhydra lutris) populations were exploited to near extinction and began to recover after the cessation of commercial hunting in 1911. When otter populations recovered after trapping was restricted, the reef rebounded, too. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. 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. 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. The 2016 survey recorded a raw count population size of 3,615, the highest survey result ever. 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. 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.). 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. Transects were digitized for the entire archipelago and of these, 61 were randomly sampled in 1992. By 2000, sea otter densities had declined to a uniformly low level throughout the archipelago (Fig. “The reefs are producing less dense skeletons,” Dr. Rasher said. In the Aleutians’ delicate seascape, otters hold the entire ecosystem together. These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. “You can travel down 10 miles of coastline and never see an animal,” he said. 3a–c) and for those islands that were at or near equilibrial density (noted as K in Figs. 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. 3d–f) in 1965. We counted sea otters with the unaided eye, using binoculars to confirm sightings or to count animals in large groups. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. The geographic extent of the sea otter population decline is unknown. That could be a difficult task, given the probable cause of the Aleutian Islands’ stunning vanishing of otters. In 2000, we resurveyed 35 transects in the western and central Aleutians. comm.). The generally high proportion of deaths from infectious disease suggests that this factor has contrib- uted to the chronically sluggish growth rate of the California sea otter popula- 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. In just a few decades, this bustling civilization has withered into a ghost town. 2000; A. M. Burdin, pers. Observed and expected distributions of proportional change in abundance between selected surveys differed significantly (P < 0.001 in all cases). 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. 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. “And temperature exacerbates that issue.”. Skiff-based surveys and related studies were supported by the National Science Foundation and the Department of Defense Legacy Program. Observers sat aft of the pilots on each side of the plane. B. The severity and geographic extent of this decline raise several conservation concerns. 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. Estimated dates for the onset of population declines of sea otters at Adak, Amchitka, and Kagalaska islands. Mean annual rates of decline were not significantly different (t = 0.06, P > 0.05). Alaskan reefs, built by the coralline algae C. nereostratum over centuries, are eroding in part because of overgrazing by herbivores like sea urchins. 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. 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. Aerial survey counts of sea otters in the Aleutian Islands, Alaska. 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. All statistical tests were considered to be significant when P < 0.05. The Alaska Maritime National Wildlife Refuge and the M/V Tiglax provided logistical-support. 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). Otter densities were log-transformed before statistical analyses. 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. “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. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. A single sea otter can scarf down nearly 1,000 sea urchins a day. 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. The islands are volcanic in origin, forming a boundary between the Bering Sea and the North Pacific Ocean. For three consecutive years from 2016 through 2018, the average southern sea otter population, which includes those found in Monterey Bay, narrowly topped the … Full Report: California Sea Otter Census Results, Spring 2017 Differences in aerial and skiff-based population trends were evaluated using a paired t-test. We conducted an aerial survey of the Aleutian archipelago in 2000 and compared results with similar surveys conducted in 1965 and 1992. “For their size and how cute they are, they are aggressive eaters.”. 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. 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. 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). We evaluated the hypothesis that otter densities varied among island groups over time. 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). 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. Diverse hypotheses have been advanced to explain the pinniped declines, but their cause (or causes) remains uncertain (National Research Council 1996). 2). 3). Continuing sea otter population declines in the Aleutian archipelago. “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. ; Estes 1990; L. Rotterman and T. Simon-Jackson, in litt. 3f). Sea otters once also occupied a large range of coastal marine environments near … For full access to this pdf, sign in to an existing account, or purchase an annual subscription. 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. Tinker, A.M. Doroff, and D.M. The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. 1 . 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. 1978), although the data are difficult to interpret because of differing survey methods. 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. By 1992, sea otters had repopulated all major island groups, although the status of populations varied among islands. Fish and Wildlife Service. 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. 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. 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. That could make it hard to sustain larger otter populations: Once introduced, they might just disappear all over again. 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. 1978; Kenyon 1969; Lensink 1962). All of these increases occurred at islands with small otter populations in 1965. From 2014 through 2017, some reefs shrank by up to 64 percent. “They eat them like popcorn,” Dr. Estes said. You wouldn’t think sea otters would affect the climate very much, but their existence keeps other parts of the ecosystem in check. The information presented in this article chronicles one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. Data from the 2000 aerial survey indicate that numbers have declined across the entire Aleutian archipelago. 2000; E. Mamaev, pers. 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. 1). 2005. 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. 1998; Hatfield et al. 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. 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