Sea otters, which were hunted to extinction in Southeast Alaska during the 18th and 19th century fur trade, were reintroduced in the 1960s. In this region, 403 animals were transplanted to six sites, predominantly on the outer coast. The population is now estimated at about 25,000 and ranges continuously along the outer coast of Southeast Alaska and interior areas including Glacier Bay. The Glacier Bay population is particularly interesting because it grew from 5 animals in 1995 to over 8000 in 2012. Such a dramatic increase is likely from both births and a movement of animals into Glacier Bay.
While this is an excellent example of exponential population growth, this growing sea otter population plays a large role in the marine ecosystem of Southeast Alaska. Sea otters are top predators, so called because they are at the top of the food chain. They have a disproportionately large role in the food chain and are designated as a keystone species. Like a keystone at the top of a stone arch that plays a critical role in holding up the arch, a keystone species play a critical role in an ecosystem.
Along rocky shores, sea otters eat sea urchins, and sea urchins eat kelp. So where there are sea otters, kelp is in high abundance. In the absence of sea otters, sea urchins can reach very high numbers and result in a barren area. Because kelp provides a place to live, hide and reproduce for many animals, for example rockfish and herring, the number of animals and plants in an area is usually higher in the presence of otters. By helping kelp forests to grow, sea otters may also indirectly help to reduce levels of atmospheric carbon dioxide, which is a major factor in climate change. A recent study showed that kelp forests play an important role in capturing carbon in coastal ecosystems.
Sea otters also eat a range of species important for commercial, subsistence, and sport fisheries. Declines in geoduck clams, abalone, sea urchins, Dungeness crab, and sea cucumber populations and fisheries have been attributed to sea otters. A recent study provides evidence that observed declines in sea cucumber populations resulted from sea otter predation over an extended period of time. Sea otters need to eat about one-quarter of their body weight per day, as they do not have blubber, like other marine mammals, to stay warm.
Although sea otters are doing well in the Southeast Alaska population stock, they are not increasing throughout their entire range. The global population has declined by more than 50 percent in the last 30 years and this pattern is expected to continue. In the US, two populations of sea otter are listed as threatened under the Endangered Species Act; the Southern sea otter in California and the Southwest stock of the Northern sea otter in Alaska. In Alaska, the population of sea otters in the Aleutian Islands (Southwest stock) declined dramatically, with declines up to 90 percent in the 1980s and 1990s.
From 6-10 p.m. on Thursday, Feb. 21 in the Egan Library, at the University of Alaska Southeast, a distinguished panel of experts on sea otters will present the latest scientific information on sea otters in Southeast Alaska, to include information on the current population status and their ecological role including foraging habits and impacts on kelp forests. A series of lectures will be followed by a question and answer session with the audience. On Friday, February 22 at 6:30 and 8pm, Jim Bodkin will present the Fireside lecture, “A Sea of Otters” at the Mendenhall Glacier Visitor Center. Both events are free and open to the public.
• Eckert is an Associate Professor of Fisheries at the Juneau Center of the School of Fisheries Sciences at the University of Alaska Fairbanks. Pearson is an Assistant Professor of Marine Biology at the University of Alaska Southeast in Juneau. Eckert may be reached at: 907-796-5450. Pearson may be reached at: 907-796-6271.