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. 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 sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. 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. Nonetheless, the population decline appears to have been relatively recent (Figs. 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. 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). “Just seeing that trend is staggering,” Ms. Boyd said. Adak Island in the central Aleutians was studied extensively in the 1990s during the population decline (Estes et al. Hence, the westward extent of the decline appears to be Attu Island. L. Comerci, A. DeGange, S. Kalxdorff, and C. Price were observers during the aerial surveys. “There was this incredible diversity,” he 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. This is a minimal estimate of abundance because some unknown proportion of the population is not detected in skiff-based surveys (Udevitz et al. An estimated 6,000 sea otters remain in the Aleutian Islands today. “The reefs are producing less dense skeletons,” Dr. Rasher said. 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.). Analytical methods.—We established early trends of sea otter abundance and distribution in the Aleutian archipelago from historical records provided by Kenyon (1969). However, in southwest Alaska, sea otters have experienced a sharp population decline in the last 20 years. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. “They eat them like popcorn,” Dr. Estes 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. 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. 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). 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.”. 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. Non-significant results are accompanied by a report of statistical power (1 − β), where β is the probability of making a type-II error. 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. 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. 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. ; V. Nikulin pers. But against the backdrop of climate change, Dr. Rasher said, the reef’s safety net is gone. 3a–c) and for those islands that were at or near equilibrial density (noted as K in Figs. 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). Fur traders in the 18th and 19th centuries hunted the animals to the brink of extinction, allowing sea urchin numbers to skyrocket, Dr. Rasher said. 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. 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. 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. “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. 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. All statistics are reported ± 1 SE, unless otherwise indicated. 1 . The number of sea otters counted decreased by 75% between 1965 and 2000; 88% for islands at equilibrial density in 1965. Sample sizes are small, but the difference in encounter rates between years is similar to that observed for nearshore aerial surveys. The information presented in this article chronicles one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history. ; K. Schneider, in litt.). "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. 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. 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. These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. An estimated 6,000 sea otters remain in the Aleutian Islands today. He doubts he will live to see the otters return. 1998). Climate change has greatly contributed to this occurrence and the decline in the sea otter population. We evaluated the hypothesis that otter densities varied among island groups over time. Sea otters are an important part of the ocean environment, but their population is declining due to human factors, disease, and killer whales. 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, … But these hidden relationships might contain hints of remedies. 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. Results of the spring 1998 southern sea otter survey indicate a 5.2 percent decline in … 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. “For their size and how cute they are, they are aggressive eaters.”. 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 … We surveyed the shoreline of each island in its entirety. :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. The sea otter population in the Aleutians has declined 70% since 1992, and 95% or more throughout much of the Archipelago since the 1980s. (ENN) -- Things are not looking good for southern sea otters. 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