SEATTLE -- Necropsy results show a Steller sea lion euthanized in Port Angeles in January was suffering from a form of cancer that is related to a sexually transmitted disease. It's believed to be the first documented case of in this species of sea lion.

The sea lion had penis cancer, which is related to herpes, according to a source close to the investigation. The only way it could have contracted the disease was through intercourse.

Wildlife officials with WDFW, NOAA and a new marine mammal rehabilitation agency, SR3, responded to the sick sea lion and analyzed tissue samples. They say that even though the sea lion had penis cancer, the cause of death was euthanasia.

The cancer is more common in California sea lions, but this is the first time it's believed to be found in Steller sea lions.

Steller sea lions are the largest kind. They can weigh more than 2,000 pounds. This stellar sea lion had lost a considerable amount of weight by the time the Feiro Marine Life Center and Washington Department of Fish and Wildlife Marine Mammal Investigations responded. An initial exam did not show signs of trauma. He was likely around 15 years old. The animal had pneumonia and a lot of fluid in his brain.

SR3 is a new marine mammal rescue and rehabilitation center. It's first of its kind in Washington. The hope is it will give marine mammals a better chance at survival when injured or sick, as well as give researchers significant opportunity to learn about wildlife.

Marine mammal strandings can be reported to the West Coast Marine Mammal Stranding Network at 1-866-767-6114.