'Unprecedented rate of cancer' in Californian sea lions

[Dr. Cara Field, Medical Director, The Marine Mammal Center]

“She's very thin. She's underweight. She was down in San Luis Obispo County and when some of the responders called her in on the beach because she was acting abnormally, kind of swaying her head back and forth a little bit, and she didn't leave the beach when people were approaching her. So all of those things tells us that there's something wrong. But we didn't know what it could be until we got her here."

When this female sea lion came ashore in California,

responders immediately knew something wasn't right.

Once she was sedated at the Marine Mammal Center in Sausalito

an ultrasound by Medical Director Dr. Cara Field showed more worrying signs

"That is a very, very bad kidney."

This sea lion was euthanized.

And unfortunately it’s a common ending for California sea lions brought here

for what has become a frequent and untreatable diagnosis: urogenital carcinoma.

A cancer that has wreaked havoc on these marine mammals.

“Many of these animals are literally fighting for their life. They they wash ashore. They strand because that's all they have left is to just find a place to haul out. And many of them are on the brink of death."

Almost 25% of adult California sea lions end up with this cancer,

according to a study published in December in Frontiers in Marine Science.

The highest prevalence of cancer in any mammal, including humans.

More worrying still – the study found two leading culprits behind the high cancer rates

long banned chemical pesticides such as DDTs and PCBs

that are being found in the sea lions' blubber tissue,

and the presence of a cancer-causing herpes virus.

"This is extraordinary and really quite awful. This is an unprecedented rate of cancer in wildlife. It's not unusual for animals to develop cancer, but it's usually as individuals or possibly small numbers. But in California, sea lions that have this urogenital carcinoma, we see unprecedented numbers. And the strong association with herpes virus and pollutants in the environment is a huge warning to us to to pay attention to what's happening in the oceans."

The study included samples from nearly 400 sea lions over 20 years.

It points to the mammals' breeding grounds near the Channel Islands in southern California

where toxic chemicals were dumped for years.

DDT was banned in the U.S. in the 1970s

And PCBs were outlawed in 1979 after being linked to cancer and other health problems.

But meanwhile, the chemicals made their way through the food chain and eventually into the blubber of sea lions.

It offers a stark warning for humans.

"One of the most important things to remember is that there is a strong association with cancer and pollutants in the environment. And that message is so incredibly important because we share some of these same resources. We'll often eat the same fish. We swim in the same water and recreate in the same water. California sea lions haul out on our coast and we certainly enjoy looking at them. But knowing that there's this presence, this huge presence, of this untreatable disease and that it's associated with toxins, with pollutants that humans have put into the environment, that really makes you think and that makes you want to take action to improve our environment, not just for the sea lions, but for ourselves as well."

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