A Keystone Species, the Sea Otter, Colonizes Glacier Bay

July 29, 2016 Posted by: Jamie Womble
Sea otters in Glacier Bay National Park
Sea otter resting near Boulder Island in Glacier Bay, July 19, 2016 (Photo: Jamie Womble/NPS)
Prior to 1911, sea otters (Enhydra lutris) were largely extirpated from southeastern Alaska by the Pacific maritime fur trade industry. In 1965, sea otters were translocated from Amchitka Island (Aleutian Islands) to the outer coast of southeastern Alaska and by the early 1990's, small numbers of sea otters were documented at the mouth of Glacier Bay. Since 1993, sea otters have expanded rapidly into Glacier Bay National Park and the most recent abundance estimate in 2012 was >8,000 sea otters, representing an average annual growth rate of 42%. In recent years, sea otters have expanded into the upper reaches of Glacier Bay including Scidmore Bay, Russell Passage, Tarr Inlet, and Adams Inlet. This rapid recolonization exceeds the theoretical maximum population growth rate, suggesting that immigration from outside Glacier Bay is also likely occurring (Esslinger et al. 2013). 
Clam shell middens made by sea otters
Clams are a primary prey item of sea otters in Glacier Bay. (Photo: Jamie Womble/NPS)
Sea otters are a "keystone species" which means that they can exert top-down pressure via predation on sea urchins, which are grazers upon kelp. As urchin density decreases from sea otter predation, so does the grazing pressure on kelp and as a result kelp forests flourish in the presence of sea otters. These top down influences on prey nearshore prey species can result in changes in community structure including maintaining a more diverse nearshore ecosystem. 
Researchers count sea otters
Lou Taylor-Thomas (NPS) and Carol Coyle (VIP) counting a group of 500+ sea otters near Point Gustavus, July 21, 2016 (Photo: Jamie Womble/NPS)
The NPS Southeast Alaska Inventory & Monitoring Network, Colorado State University, the USGS Alaska Science Center, Glacier Bay National Park, and the NPS Southwest Alaska Inventory & Monitoring Network recently initiated a study to better understand the spatial distribution, abundance, and colonization dynamics of sea otters in Glacier Bay National Park. This new research effort builds upon existing sea otter distribution and abundance data by using aerial photographic surveys with contemporary modeling methods to develop an adaptive monitoring framework that minimizes model uncertainty and maximizes survey efficiency. The project will provide a foundation for understanding the colonization dynamics of sea otters and their influence on nearshore communities in Glacier Bay National Park.  
Aerial photograph of sea otters in a kelp bed
Aerial photograph of sea otters resting in kelp near Ripple Cove in Glacier Bay, July 6, 2016 (Photo: Jamie Womble/NPS)
Visit the Voices of Glacier Bay webpage and scroll down to Sound #8 to hear sea otters munching on shellfish in Glacier Bay.
For more information, please contact Dr. Jamie Womble (jamie_womble@nps.gov).

Last updated: July 29, 2016

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