SAN FRANCISCO (KPIX) – For decades, sea lions along the West Coast have been plagued by a lethal form of cancer. Now, research conducted at the Marine Mammal Center has determined the cause of the disease and how it holds both promise, and shame, for mankind.

The sea lions that hang out at Pier 39 are always a tourist favorite and 4-year old A’nayah Langston doesn’t want anything bad to happen to them.

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“They need to be safe and they need to live in…in…a safe place!” she said.

But they haven’t been safe for a long time. In 1979, the Marine Mammal Center in the Marin Headlands began finding sea lions dying from a cancer called “urogenital carcinoma.”

Since then, up to one quarter of all adult sea lions admitted to the hospital have died from it. It’s been a mystery until now. Researchers have discovered the cancer is caused by a sea lion-version of genital herpes.

“It’s a sexually transmitted virus, which is actually a very efficient way to spread if you’re a virus, because you have to reproduce to keep the species going,” said Dr. Alissa Deming, lead author of the cancer study.

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Deming studied the outbreak for four years at the Marine Mammal Center and said man has a hand in this, as well. It’s believed that contaminated water is triggering the virus to induce cancer. Recently, it was discovered that thousands of barrels of the banned pesticide DDT were dumped in the ocean in the 1970s off the Southern California Coast and the Channel Islands, the place where 90 percent of sea lion pups are born.

“It’s like the last place you want a bunch of contaminants to be is in your nursery and the Channel Islands is that place,” said Dr. Deming. “It is absolutely that these contaminants are impacting the entire population of California sea lions across the West Coast of the United States, not just California.”

In a bitter irony, the sea lion cancer is similar to cervical cancer in humans, so studying it may unlock some answers to preventing it in people. Sadly, Dr. Deming said there are no treatment options for the sea lions but she would like to see something good come from their deaths.

“We can utilize these animals, kind of respect them in their death, by taking advantage of learning as much as we can from them,” she said.

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Dr. Deming credits the Marine Mammal Center and its former Senior Scientist, Dr. Frances Gulland, for recognizing the spike in cancer cases and saving tissue samples starting in the mid-1990s. Those samples, from more than 300 animals, are helping drive the research.