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When an adult female sea lion landed in San Luis Obispo Cou in central California recently, responders immediately knew something was wrong.
She was thin and underweight, rocked her head back and forth and didn’t run away as people approached, said Dr Cara Field, medical director of the Marine Mammal Center in Sausalito.
“All of these things are telling us that there is something wrong, but we didn’t know what it could be until we brought him here,” said Field.
Once the sea lion was sedated and intubated in a quarantine cell in the centre’s grounds for an ultrasound, more worrying signs appeared.
“It’s a very, very bad kidney,” said Field, leaning over the sea lion while looking at the ultrasound screen. “With cancer, what we often see is that the cancer has metastasized.”
The sea lion inspected that day was euthanized, a common end for California sea lions brought here for what has become a frequent and incurable diagnosis: urogenital carcinoma.
It has wreaked havoc on these marine mammals.
According to a study published in December in Frontiers in Marine Science, nearly 25 percent of adult California sea lions end up with this cancer, the highest prevalence of cancer in all mammals, including humans.
“It’s amazing and really pretty awful,” Field said. “This is an unprecedented rate of cancer in wildlife. “
The study found two main culprits behind the high rates of cancer – long-banned chemical pesticides such as DDT and polychlorinated biphenyls (PCBs) found in the fat tissue of sea lions and the presence of a sea lion virus. carcinogenic herpes known as the otarin herpes virus (OtHV-1).
“Very few animals with cancer did not have the virus,” said Dr Padraig Duignan, director of pathology at the center and co-author of the study. “But then when you looked at the levels of chemicals in their fat and took that into account, the presence of the chemicals and their level increased the likelihood of cancer to between 30% and 80%.”
The study included samples from nearly 400 sea lions over 20 years. Field and Duignan see these patients regularly, as Field often oversees admission exams and ultrasounds while Duignan performs autopsies.
In autopsies, scientists do a complete dissection. They also look for metastases that spread to other parts of the body, including the lymph nodes, abdominal cavity, and chest cavity.
Duignan pointed to the mammalian breeding grounds near the Channel Islands in southern California where toxic chemicals have been dumped for years.
A Los Angeles Times investigation last year revealed “thousands of barrels of acid sludge” containing DDT dumped near Santa Catalina Island in the years following World War II. Sediment samples showed DDT levels 40 times greater than the amount detected at a nearby EPA-designed hazardous waste site.
DDT was banned in the United States in the 1970s, and PCBs were banned in 1979 after being linked to cancer and other health problems.
But the chemicals made their way through the food chain and eventually into the fat of sea lions.
Field and Duignan both believe sea lion cancer is a stark warning to humans.
Field said: “The strong association with the herpes virus and pollutants in the environment is a huge warning for us to pay attention to what is happening in the oceans.”
“Knowing that there is this presence… that makes us want to take action to improve our environment, not just for the sea lions but for us as well,” said Field.
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