A quarter of adult California sea lions die of cancer, and a sexually transmitted virus may be to blame

Cancer at Sea

At the Marine Mammal Center in Sausalito, more than a quarter of adult California sea lions that die arrive with an aggressive cancer that starts in the reproductive organs and can turn vertebrae to mush. Researchers have identified a previously unknown herpesvirus in the tumors of every cancerous animal, likely spread through sexual contact, though they haven't proven it causes the disease. With pups also starving amid warm water and toxic algal blooms, the population's future is uncertain.