2013-2017 California Sea Lion Unusual Mortality Event in California
Elevated strandings of California sea lion pups and yearlings occurred in Southern California between 2013 and 2017. NOAA Fisheries declared these strandings to be an Unusual Mortality Event.
Elevated strandings of California sea lion pups have occurred in Southern California since January 2013. This event has been declared an Unusual Mortality Event. The UME is confined to pup and yearling California sea lions. Many of the sea lions are:
- Very underweight for their age.
This event is occurring in the same areas as the ongoing 2015-2018 Guadalupe fur seal UME.
Causes of the California sea lion UME
Our findings to date indicate that a change in the availability of sea lion prey, especially sardines, a high value food source for nursing mothers, is a likely contributor to the large number of strandings. Sardine spawning grounds shifted further offshore in 2012 and 2013, and while other prey were available (market squid and rockfish), these may not have provided adequate nutrition in the milk of sea lion mothers supporting pups, or for newly-weaned pups foraging on their own.
Although the pups showed signs of some viruses and infections, findings indicate that this event was not caused by disease, but rather by the lack of high quality, close-by food sources for nursing mothers. Current evidence does not indicate that this UME was caused by a single infectious agent, though a variety of disease-causing bacteria and viruses were found in samples from sea lion pups. Several different kinds of astrovirus, including some new species of astrovirus, were identified in a high percentage of the samples. However, the importance of this finding is still under investigation.
Investigating and identifying the cause of this UME is a true public-private effort with many collaborators. The investigative team examined multiple potential explanations for the high numbers of malnourished California sea lion pups observed on the island rookeries and stranded on the mainland in 2013. The examination of the root causes of the California sea lion UME fall squarely within NOAA Fisheries' core missions to protect and conserve marine mammals. The UME investigation is ongoing.
Rehabilitating stranded California sea lion pups
The pups that were rescued and rehabilitated had a high rate of survival. After stranding network member rehabilitation centers provided malnourished, stranded pups with nutrition and hydration, over 50 percent survived to be released. For the animals outfitted with a satellite tag, tracking data show most survived following release.
Report a stranding
If you encounter a stranded California sea lion or other marine mammal, alive or dead, do not approach it. You can report any stranded marine mammal to the marine mammal stranding network. Numerous organizations around the country are trained and ready to respond.
- Marine Mammal Health and Stranding Response Program.
- Marine Mammal Protection.
- Report a stranded sea lion or any marine mammal, alive or dead, to the marine mammal stranding network.
- Unusual Mortality Events.