CSI Sea Otter: The dead DO tell tales

CWS wildlife veterinarian Tristan Burgess, joins a team lead by the California Department of Fish and Wildlife, in compiling one of the most extensive and thorough studies consisting of one specific wildlife population. Over a period of 15 years, 560 deceased southern sea otters were examined to understand their causes of mortality. Many of these animals had been previously tagged and monitored to better understand their ecosystem, habitat use and foraging behavior. Sea otters live in the intertidal zone, making them a key indicator species in determining water quality and aiding researchers discover direct sources of land pollution entering waterways.

The results from the study showed that the most common primary cause of death to sea otters was shark bite, which increased markedly during the 15 years with infectious diseases as the leading contributing cause of death. Sea otters can also be sentinels of ocean health for humans - one of the most common toxins found in deceased sea otters was Domoic Acid, DA. This toxin represents a  significant risk to humans, and has increased exponentially in California waters due to climate change. When found at unsafe levels, fisheries are shut down to lessen the risk of human contact however, sea otters continue to consume the crabs and bivalves which contain high levels of DA. This study  identified areas where mortality rates were higher due to DA intoxication, allowing researchers to pinpoint possible sources of land pollution entering waterways. 

Closely monitoring and interpreting sea otter health and causes of mortality can help government agencies and communities pursue better conservation efforts and policies to improve human health and restore the sea otter population. Future work is using these findings to better understand the population-level impacts of various causes of mortality and model how they impact the future population trends for this ESA-listed threatened species.

Read the full Sea Otter Mortality Study 

Read more about CDFW’s sea otter program