USGS Western Ecological Research Center

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The California Sea Otter Stranding Network is part of the USGS effort to monitor southern sea otters (Enhydra lutris nereis) and provide data to the U.S. Fish and Wildlife Service.


The number of sea otter strandings in 2012 (368) was another record high, surpassing the number in 2011 by 33 animals (see spreadsheet tables 1-3).

A stranded sea otter is one that washes ashore dead or alive. Most sea otters that strand alive die or are euthanized shortly thereafter. Some get treatment and survive through rehabilitation (but would have died without treatment). The vast majority, however, are dead when they strand. 

The record number of strandings observed this year can again be partly attributed to more sea otters being bitten by white sharks, a cause of death that has been increasing steadily over the last decade. An increase in shark bitten otters explains, in part, the record stranding totals in January, February, June, July and December (spreadsheet Table 3). A high proportion of stranded animals were found with shark bite wounds along the shores of Estero Bay and Pismo Beach in 2012, and there was another increase in bitten carcasses found on the shores of Monterey Bay (following the increase observed in 2011 compared to previous years) – both in the total number bitten and the proportion bitten (spreadsheet Table 1). 

Stranding locations and field age composition of the stranded animals in 2012 were very similar to that seen in 2011. Slightly more males than females stranded in 2012 (spreadsheet Table 2).

Efforts are made to recover and examine each reported sea otter carcass, and a subset of fresh carcasses are sent to the CDFG Marine Wildlife Veterinary Care and Research Center, where veterinarians conduct necropsies to determine the primary causes of death and identify factors that may have contributed to the death of each animal. Final determinations on cause of death are made after laboratory results are received, and the final records are provided by the CDFG Marine Wildlife Veterinary Care and Research Center.

NOTE: Stranding numbers only account for sea otters that people find, including any dead animal, or stranded live animal that would have died without intervention. Past research indicates that possibly less than 50% of sea otters that die in the wild end up on the beach, so the data presented here at best provide only an index of trends in population mortality.


Updated 2013.07.19

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