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. Non-significant results are accompanied by a report of statistical power (1 − β), where β is the probability of making a type-II error. ; K. Schneider, in litt.). 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. 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. 1). 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. 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 number of sea otter pups, which represent the future of the species, is down 11 percent. These colonies subsequently increased to repopulate much of the sea otters' former range. 1978; L. Rotterman and T. Simon-Jackson, in litt.). B. 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. All of these increases occurred at islands with small otter populations in 1965. Warmer temperatures also speed animal metabolism, driving urchins to eat even more enthusiastically than usual. Skiff-based surveys and related studies were supported by the National Science Foundation and the Department of Defense Legacy Program. Continuing lack of growth in the range peripheries likely explains the cessation of range expansion. 1998). That could be a difficult task, given the probable cause of the Aleutian Islands’ stunning vanishing of otters. 3a–c) were distinctly bimodal, indicating that, although otter numbers at most islands were in decline during this period, they increased markedly at others. 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. The number of sea otters counted decreased by 75% between 1965 and 2000; 88% for islands at equilibrial density in 1965. comm. Many individuals assisted with the skiff-based surveys throughout the 1990s, including D. Irons, J. Meehan, D. Monson, and J. Stewart. Otter densities were log-transformed before statistical analyses. We evaluated the hypothesis that otter densities varied among island groups over time. 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. 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). 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. ); it is unclear whether equilibrial density had been reached before the onset of the decline. Behavior. Overflights of Steiler sea lion haulout and rookery sites were permitted under the National Marine Mammal Laboratory's ESA/ MMPA Permit 782-1532-00. National Research Council 1996). 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. Sea otters are an important component of the ocean environment. The 2016 survey recorded a raw count population size of 3,615, the highest survey result ever. The geographic extent of the sea otter population decline is unknown. The frequency distributions of the first 3 contrasts (Figs. “Predator loss can impact the environment in ways we haven’t even thought of,” Dr. Griffin said. In 2000, we resurveyed 35 transects in the western and central Aleutians. 2; Table 1). 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. 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. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. “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. 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. Skiff-based surveys at Attu Island (Fig. But sharks are only part of the problem. When otter populations recovered after trapping was restricted, the reef rebounded, too. 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. Transects were digitized for the entire archipelago and of these, 61 were randomly sampled in 1992. Kelp provides shelter for sea otters and their pups and a variety of other marine organisms. Hence, the westward extent of the decline appears to be Attu Island. Results of the spring 1998 southern sea otter survey indicate a 5.2 percent decline in … Survey methods in 1992 and 2000 were similar with respect to air speed, altitude, distance from shore, and personnel. 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). Everywhere the young biologist looked, there were sea otters — lollygagging on kelp beds, shelling sea urchins, exchanging their signature squeals. 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. When the oceans had been healthy, the team found, nips from urchins had barely scuffed the algae’s surface. We computed independent rates of population change from skiff-based counts conducted in the western and central Aleutian Islands. From 2014 through 2017, some reefs shrank by up to 64 percent. 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. 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. 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. These differences demonstrate population declines between 1965 and 1992 and between 1992 and 2000, for all of the islands in the Aleutian archipelago (Figs. 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. 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). 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. Collectively, these efforts chronicle a pattern of population recovery that began in the central Aleutians and gradually spread throughout the archipelago. 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. The algae’s decline also seems to be speeding up. ESTES ETAL. 1 . 2000; Kenyon 1969). Expected distributions were computed from a lognormal density function with a mean of 1 and the observed variance. 1) when viewing conditions were good to excellent (Beaufort sea state of 1–2, and >1 km of clear visibility at sea level). “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. We evaluated the null hypothesis that there was no difference between observed and expected distributions. 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). “It was spectacularly beautiful.”, When the Otters Vanished, Everything Else Started to Crumble. 2000; Kenyon 1969). During the past 15–20 years, sea otters Enhydra lutris in the Aleutian Islands, Alaska, USA, experienced a drastic decrease in population size. Aerial surveys were funded by the United States Fish and Wildlife Service, United States Geological Survey, and United States Navy. For many years, there were no sea otters in Canadian waters and most of the sea otters in the world were … The severity and geographic extent of this decline raise several conservation concerns. It’s one reason for a worrying decline in the number of California sea otters. Cloud cover, Beaufort sea state, wind speed, and visibility conditions were recorded at the beginning of each segment. 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. A single sea otter can scarf down nearly 1,000 sea urchins a day. By 2000, sea otter densities had declined to a uniformly low level throughout the … “There was this incredible diversity,” he said. The latest count of this threatened species shows their population dropped to just 2,711, a decline of 3.6 percent. We surveyed the shoreline of each island in its entirety. The sea otter preys on urchins in Alaska, which allows the kelp forests to thrive as well. The survey crew consisted of a pilot, copilot, 2 observers, and 1 data recorder. Continuing sea otter population declines in the Aleutian archipelago. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. 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. 2019). Sample sizes are small, but the difference in encounter rates between years is similar to that observed for nearshore aerial surveys. Nonetheless, the population decline appears to have been relatively recent (Figs. If there is a decline in sea otters due to natural predation or other factors such as an oil spill, urchin populations explode. You wouldn’t think sea otters would affect the climate very much, but their existence keeps other parts of the ecosystem in check. Observers sat aft of the pilots on each side of the plane. Analytical methods.—We established early trends of sea otter abundance and distribution in the Aleutian archipelago from historical records provided by Kenyon (1969). Full Report: California Sea Otter Census Results, Spring 2017 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.). A.. Estes J. 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- We fitted decline trajectories to the survey data using least squares, assuming an exponential function of the form Nt = N0ert. However, though the protective history of the sea otters looks promising for their future, this nation’s wasteful and lazy attitu… Fish and Wildlife Service. The International Fur Seal Treaty protected the surviving remnant colonies from further harvest beginning in 1911. 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. 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). 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