From April to October of 1988, thirty eight California sea lions (Zalophus californianus) and ten northern fur seals (Callorhinus ursinus) were found depressed or convulsing on the beach. For every live animal rescued, there were up to ten dead animals on the same stretch of beach. All animals had at least one seizure during or after rescue, and most had multiple seizures. Seizures were characterized by tremors up to grand mal types. Thirty two California sea lions and all ten northern fur seals were rescued from a twenty mile stretch of coastline in San Luis Obispo county. One animal came in twenty miles north of the San Luis Obispo. The other five animals came from Monterey and further north. Twenty four of the thirty two California sea lions and four of the ten fur seals from San Luis Obispo area were alive when they reached the California Marine Mammal Center. There were two males and thirty six female sea lions, and two male and eight female fur seals from the San Luis Obispo area. Five of the fur seals were pups.

Of the thirty four live animals that came to the California Marine Mammal Center with a seizure history, twenty four sea lions (80%) and three fur seals (75%) survived and were released back to the wild. Most of these animals had one to two seizures per day from one day up to three weeks. Two California sea lions had almost continuous tremors and were unaware of their surroundings for over two weeks, and recovered. All animals were in excellent physical condition when they were admitted, and had normal blood parameters. Heavy metal serum analysis was run on eight animals. One sea lion had a significantly high serum lead level of 0.7ppm. Other animals tested were within normal limits. Postmortem examination of tissues revealed that most of the animals that died had probably aspirated sea water while convulsing in the ocean. Other tissue analysis revealed nothing conclusive. Results are still pending for chlorinated hydrocarbon analysis.

Treatment consisted of controlling the seizures with diazepam as needed, and fluids. Animals that had aspirated sea water were treated with Mucomyst and were percussed.

The differential diagnosis includes poisoning, either deliberate or environmental, or a virus. Poisons would include heavy metals, chlorinated hydrocarbons, organophosphates or possibly a deliberate poisoning such as lithium chloride or strychnine. The seizuring animals were housed adjacent to animals with other problems, and the seizure syndrome was never transmitted to another animal.