Dead Whale Washes Ashore : Migration: Biologists will perform a necropsy to try to determine what killed the 35-foot creature off Seal Beach.

A gray whale, believed to be about 35 feet long, washed ashore here Sunday night, hours after boaters spotted its carcass floating off the city pier.

Biologists from the Natural History Museum in Los Angeles, who went on a boat to view the whale, said they would not be able to determine the cause of death until they perform a necropsy beginning this morning.

John E. Heyning, assistant curator of mammals from the museum, said there is no evidence that the whale had been entangled in a gill net, a controversial fishing net that has been responsible for other sea mammal deaths.

“There is no indication of that at this time,” he said. “However, we haven’t seen the whole animal yet, so we don’t know.”

In February, an 18-foot gray whale was found washed ashore near Laguna Beach’s Victoria Beach, and authorities determined that its death may have been caused by a gill net which entangled it and caused it to suffocate. Last year, he said, about four gray whales washed onto Orange County and Los Angeles County beaches and two of them had died from being entangled in gill nets.

Heyning said biologists want to examine the dead whale that washed ashore Sunday both to determine the cause of death and to learn more about these mammals also known as baleen whales. A federally protected animal on the endangered species list, the gray whales are difficult to study at sea. They mate in the warm Baja California waters of Mexico and migrate north to the chilly Alaskan waters during this time of the year.

“This is the right season (for their migration), so it’s not out of the ordinary to find one washing up dead,” Heyning said.

And their deaths can be caused by a variety of factors.

“They could be attacked by a killer whale; they can get a wide variety of diseases, like pneumonia, or sometimes they do get caught in nets,” he said.

He said museum biologists would transport parts of the whale to their laboratory for study. They will drive down in one of two specially designed trucks manufactured by Ford to haul dead mammals from beaches. The Smithsonian Institution in Washington owns the other one, he said.

“What we hope to do is to collect the skull, which is useful for scientific research,” Heyning said. “We want to look at its stomach content to see what it was eating, we examine whether it was sexually mature and hopefully we’ll find out cause of death.

“To a great extent what we really want to do is examine how they live in their environment. That’s almost more important, to find out how they lived, than to find out why they died.”