California Sea Lions Struggle Against a Deadly Trifecta


Teun – One of the California sea lions that I work with at the Marine Science Center


Scientists Investigate a Mysterious Cancer Plaguing California Sea Lions

Back in 2013, I wrote a brief post about mass sea lion strandings occurring in California. However, the article that I provide today is much more in-depth about sea lion health in California in general and includes the progress that has been made in the last couple years in terms of understanding why California sea lions have been stranding more frequently. (The article above is rather graphic in nature, so if you are not a fan of necropsies, maybe just stick to reading my post.)

The article focuses on research being done at The Marine Mammal Center (TMMC) in Sausalito, CA, to better understand cancer, pollutant exposure, and domoic acid poisoning in California sea lions. The aggressive cancer plaguing the sea lions appears to initially target the reproductive organs and then spread to an animal’s spine. Over 25% of the sea lions admitted to TMMC have cancer. From DNA analysis of cancerous tissues, researchers have discovered a new strand of herpesvirus that appears in high concentrations in sea lion tumors and is rarely found in health sea lions. Apparently, no definitive link between the virus and the cancer exists yet, but they are thought to be connected. An important finding from the necropsies done at TMMC is that sea lions with cancer also have high quantities of the pollutants PCB and DDT stored in their blubber. Scientists believe that the pollutants could lower the immune response of the sea lions, thereby making them more susceptible to cancer.

Environmental pollutants may also be contributing to the rise in domoic acid poisoning in marine wildlife. Domoic acid is a toxin produced by dangerous algal blooms. The blooms appear to thrive on pollutants that we add to the water supply via septic tanks, runoff, fertilizer, etc. The domoic acid produced by the bountiful blooms is absorbed into fish and concentrates in apex predators that consume these infected fish, such as sea lions. Subsequently, sea lions may become poisoned by the toxin and exhibit symptoms, including seizures. Domoic acid exposure, combined with warming waters, has led to mothers being unable to properly rear their pups, further contributing to sea lion strandings. I found a short news video that follows TMMC staff as they explain more about California sea lion health. It is slightly depressing because the clip shows sea lions having seizures, but I think it is good that the film crew did not try to sugar-coat everything for the audience.

I really enjoyed this article because it intertwined the human health aspect and mentioned the idea of the One Health initiative. The One Health initiative is about taking a multi-disciplinary approach to the health of humans, wildlife, and the environment and acknowledging that the three aspects are inter-related (Video). The article stressed the One Health idea by showing how important it is to understand cancer and diseases in indicator species, like sea lions, because sea lions consume the same fish that people do. (Sea lions are basically becoming the Freddie Foreshadowers for human health).

I also wanted to do a post on this article because I am a huge fan of TMMC. During my time as a Master’s student, I received funding to go visit the facility for a week, assist with necropsies, and collect some whisker samples. I even got to help with a humpback whale beach necropsy!! (I will forego pictures… and smells! Haha). I had a fantastic experience there, and out of all of the institutes that I contacted about obtaining whisker samples for my graduate research, TMMC was hands-down the best. TMMC researchers adamantly stick to a science first philosophy, which I loved. They were not focused on charging bizarre fees for their samples, they just wanted to help scientists get as much information and data out of each animal as possible. Evidently, TMMC is participating in 40 different collaborative projects! How great is that!? If this post was a little too depressing for you, take a few minutes to watch this video of a sea lion pup at the Pittsburgh Zoo learning how to swim! Enjoy the rest of your weekend!


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