Sea lions off the California coast are increasingly facing a terminal diagnosis, one potentially linked to toxic, human-made chemicals from generations ago.
A report from Reuters found that California sea lions are increasingly being diagnosed with urogenital carcinoma, a startlingly common form of vital cancer among these water mammals. These creatures have the highest rates of cancer among any mammal, including humans.
The finding is part of a study co-authored by researchers at the Marine Mammal Center and published in the peer-reviewed Frontiers in Marine Science journal.
An estimated 18 sea lions necropsied by the Marine Mammal Center between 1979, when the cancer was first discovered, and 1994 had that form of cancer. That rate has only grown in recent years. Almost a quarter of adult California sea lions, per a study published last December, were diagnosed with the cancer.
“This is extraordinary and really quite awful,” Marine Mammal Center medical director Cara Field told Reuters. “This is an unprecedented rate of cancer in wildlife.”
Many of these sea lions were found to have OtHV-1, or Otarine herpes virus — a virus detected in the genital tract. That could be a key factor in these sea lions’ diagnosis. A recent study published in the journal Animals noted that sea lions without cancer tested positive for the same virus, but in much lower rates than those diagnosed with cancer.
The virus is also likely linked to pesticides found in deceased sea lions’ blubber. The presence of products like DDT insecticides in their blubber was linked to a higher probability of cancer. DDTs were banned in the United States in 1972.
Padraig Duignan, a pathologist at the MMC, told Reuters that sea lions breed near a toxic waste site near the Channel Islands — an area in which nearly 25,000 barrels believed to be storing DDT were found in April.
“Even though some of the pollutants we’re finding in the blubber have been out of use for years, these cancer-causing elements remain in the environment for a very long time and wreak havoc on opportunistic coastal feeders like sea lions,” Duignan said in a statement. “It concerns me knowing that we consume very similar seafood as these cancer victims and that the ocean is raising a loud and clear alarm in the sick bodies of a sentinel species.”