Sea otters luxuriating in the waters of Glacier Bay. NPS Photo
New Arrivals
Sea otters, once nearly eliminated by fur hunters, have made a spectacular comeback throughout the North Pacific following protection in 1911 and reintroductions about 30 years ago. But until recently, otters had not found their way into Glacier Bay. Now that has changed - presenting the National Park Service with a unique opportunity to understand more about the effect of the otters' return on the ecosystem.
Rapid Population Growth
Since 1995 when the first five otters were observed in Glacier Bay, the population has grown to an estimated 8,000 individuals. Most of these animals are concentrated in lower reaches of the Bay. Sea otters consume large quantities of clams, mussels, crabs and other invertebrates, some of which are commercially, culturally or ecologically important. Scientists have long known that increased predation on these species can cause long-term changes that ripple through the ecosystem.
Sea otters are now abundant in the waters of Glacier Bay. NPS photo
Reproduction
Alaska sea otters typically bear their pups in late spring ― one pup per breeding cycle. But, depending on the availability of food, breeding may occur every other cycle. Pups weigh only a few pounds at birth, typically 3-5 pounds (1.4-2.3 kg) and are light brown. They live on top of their mothers, literally, until they are weaned. That's where they eat, sleep and how they travel, although otters usually don't roam far, unless they've run out of food.
Threats
Many sea otters live15–20 years. Orcas are a primary predator of adult otters, and newborn otters are sometimes preyed upon by bald eagles.The greatest threat to the sea otter remains humans. It has been estimated that the 1989 Exxon Valdez oil spill caused the deaths of more than 2500 sea otters. Otters are also caught in fishing nets, and hunted for subsistence by Alaskan Natives.
What Impact Might an Otter Have on Glacier Bay?
Sea otters inhabit near shore waters that are less than 54 m (177.17 feet) deep. Their habitats are near reefs, rocky shores and thick kelp forests. These kelp forests are dependent on the otter to protect them from excessive grazing by the otters' prey. Increased and rapid otter colonization in Glacier Bay is due to the immigration of adults and juveniles and to reproduction, as evidenced by the increasing number of dependent pups. As sea otters continue to colonize Glacier Bay, dramatic changes will most likely occur in the type, abundance and size of many species in the nearshore marine ecosystem.
Since sea otters were not seen here before 1995, Glacier Bay provides the perfect opportunity to study an area before and after their introduction and learn exactly how these changes occur. In order to accurately describe and understand the magnitude of the otters' likely effect on the region's ecosystem, researchers are currently studying:
the number and location of the otters and the population's growth rate.
the number and variety of prey eaten by otters
the number and variety of species found on the sea floor
These studies will enable park managers to differentiate naturally occurring changes from those that are human-induced.
Read a summary and link to a published paper that describes prey selection changes as sea otter populations increase: Leach, C. B., B. P. Weitzman, J. L. Bodkin, D. Esler, G. G. Esslinger, K. A. Kloecker, D. H. Monson, J. N. Womble, and M. B. Hooten. 2024. The dynamics of sea otter prey selection under population growth and expansion. Ecosphere 15(12): e70084.
Buried in debris for decades, Drakes Estero is now one of the few remaining undeveloped estuaries on the U.S. Pacific coast. After a massive cleanup, scientists tracked the regrowth of an eelgrass community there—and found it transformed.
Offices:San Francisco Bay Area Inventory & Monitoring Network
Recently, a team of scientists chose southern sea otters to test if predator-prey population dynamics modeling could help conservation planners figure out where predator reintroductions could work. The team published their results in June. They found that two estuaries in Point Reyes National Seashore could probably feed lots of cute (or not) whimsical water weasels one day!
Read a summary and get the link to an article about modeling sea otter populations in Alaska: Hasan, E. L., K. B. Gorman, H. A. Coletti, and B. Konar. 2024. Species distribution modeling of northern sea otters (Enhydra lutris kenyoni) in a data-limited ecosystem. Ecology and Evolution 14(3): e11118.
Read a summary and link to a paper documenting wolves and bears hunting marine mammals: Griffin, K. R., G. H. Roffler, and E. M. Dymit. 2023. Wolves on the Katmai coast hunt sea otters and harbor seals. Ecology e4185.
Read the abstract and link to an article about coastal brown bears and sea otters in Katmai Naitonal Park and Preserve: Monson, D. H., R. L. Taylor, G. V. Hilderbrand, J. A. Erlenbach, H. A. Coletti, K. A. Kloecker, G. G. Esslinger, and J. L. Bodkin. 2022. Brown bear-sea otter interactions along the Katmai coast: Terrestrial and nearshore communities linked by predation. Journal of Mammalogy pp. 1-13.
Locations:Katmai National Park & Preserve, Kenai Fjords National Park, Lake Clark National Park & Preserve
Read the abstract and get the link to an article about how to potentially detect impacts of harmful algal blooms in higher-trophic levels of the ecosystems: Bowen, L., S. Knowles, K. Lefebvre, M. St. Martin, M. Murray, K. Kloecker, D. Monson, B. Weitzman, B. Ballachey, H. Coletti, S. Waters, and C. Cummings. 2022. Divergent gene expression profiles in Alaskan sea otters: An indicator of chronic domoic acid exposure? Oceans 3(3): 401-418.
Share the wonderful world of sea otters with students with "Swimming on Your Back." This educational package focuses on the natural history and ecology of sea otters in Alaska.
2020 Resource Brief, Nearshore Marine Systems. Many species depend on nearshore habitats, including several with well recognized ecological roles in the nearshore food web. Our work describes patterns of change in those species and identifies probable causes in order to support management and policy decisions for nearshore resources. This article describes recent findings of the nearshore marine system components related to the marine heatwave of 2014-2017.
Sea otters, once hunted to near extinction in the northern Pacific Ocean, may be returning to Lake Clark National Park and Preserve’s coast. What would that mean for the ecosystem?
