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TASSC SEA OTTER PROJECTS > Sea Otter Winter Mortality Survey

Program Description: The objective of this project is to document sea otter deaths over winter in a standardized area. Also, trends such as general age ratios, sex ratios and mortality of sea otters are tracked. To accomplish this, good beachcombing beaches are identified and each year, someone walks the beach in the spring looking for dead otters. If dead otters are found and identification is possible, age is estimated, sex is determined and a muscle sample and a tooth are collected.

History: The Winter Sea Otter Mortality Survey program followed the successful Sea Otter Biosampling Program. Typically, in any given animal population, some old and young animals are expected to die over winter. The surveys provide a way for communities to assess the winter mortality of their local growing sea otter population. In 1996, the late George Shelikoff, a trained Sea Otter Biosampler, observed and investigated an unusually large but natural die-off event in False Pass. George determined the die-off was from fast shore ice and unusual freezing temperatures that created hypothermia in the sea otters. George’s call prompted TASSC to provide funds to the community for investigating and documenting this localized sea otter mortality event.

Sea Otter Winter Mortality Survey training in Seldovia, Alaska. Photo © TASSC.



Sea Otter Winter Mortality Survey training in Seldovia, Alaska. Photo © TASSC.



Marine mammal bones found during a Winter Mortality Survey. Photo © TASSC.


  • Another mortality event began near Cordova in 1995 and prompted TASSC to fund Native Village of Eyak efforts to determine the causes. Coordination between the researchers, city officials and local fish processors occurred and the mortality has decreased by 90%.
  • In Bristol Bay, fast shore ice can occupy a sea otter’s habitat overnight and sea otters may attempt a 30 mile migration across land to the Pacific Ocean side. This event prompted TASSC to fund local investigations and document the overland sea otter mortality in this unusual event. Through local and traditional knowledge such an event is known to occur periodically and documentation is vital to the history of the northern sea otter.
  • Sea Otter Winter Mortality Surveyors also report all dead stranded marine mammals, contributing to the Alaska Marine Mammal Stranding Network.
  • Sea Otter Winter Mortality Surveys have been conducted in Cordova, False Pass, Port Heiden, Sitka and Yakutat.

Current/Future plans: TASSC, with Section 119 funds, will continue with supporting communities presently documenting over-winter die-off trends of their growing sea otter population. For 2006, surveys will be conducted in Cordova, Seldovia and Yakutat. Due to the unpredictable nature of the species, TASSC will continue to be ready for unusual mortality event investigations.



© 2005 The Alaska Sea Otter & Steller Sea Lion Commission 
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