California Sea Otter Stranding Network

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TRENDS IN SEA OTTER MORTALITY


Since 1968, biologists and veterinarians at the California Department of Fish and Game (CDFG) and the USGS Western Ecological Research Center have documented and examined all reported sea otter strandings -- counting the number of dead, sick or injured sea otters recovered along California each year -- in an effort to understand the population trends of the southern sea otter (Enhydra lutris nereis), a federally listed threatened species.

This effort was begun by CDFG, but soon became a multi-agency and multi-organization endeavor. The coordination of the sea otter stranding network was transferred to USGS scientists in 1995.

In addition to the CDFG Office of Spill Prevention and Response and USGS, other institutions including the Monterey Bay Aquarium, US Fish and Wildlife Service, California Academy of Sciences, Santa Barbara Museum of Natural History, The Marine Mammal Center, various city beach clean-up crews and others contribute by reporting and/or retrieving carcasses. Live sea otters that strand ashore in California are reported to and retrieved by the Monterey Bay Aquarium or The Marine Mammal Center, and are included in the stranding data set.
 
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.