A cause of death couldn't be determined Friday for a 20-foot-long young gray whale that washed up on Dillon Beach this week.

A team from the Marine Mammal Center and California Academy of Sciences went to the site near Lawson's Landing to see if they could determine how the whale died.

"The team got back from the necropsy and they were not able to determine cause of death due to the advanced decomposed state of the whale," said Jim Oswald, mammal center spokesman. "They did collect some bones which will be used for future study."

The same whale's carcass had grounded at Marshall Beach in Tomales Bay last week. Researchers had difficulty getting to it and it was towed into the ocean and released, only to be swept back in by tides.

A dead gray whale is pictured on beach near Marshall in Tomales Bay earlier this month. (John Krug photo)
A dead gray whale is pictured on beach near Marshall in Tomales Bay earlier this month. (John Krug photo)

This time the whale will be left to decompose or be washed out by the tides. Because it has decomposed it's not likely to float into shore again, Oswald said.

The gray whale was the second whale to wash up on Marin shores this month. Two weeks ago the body of an endangered humpback whale washed up on Coast Camp Beach in the Point Reyes National Seashore. It had some shattered bones, suggesting it may have been hit by a ship.

Beginning this month, busy shipping lanes off the Marin coast were adjusted to protect endangered whales from being hit by ships.

The International Maritime Organization approved the vessel lane changes on approaches to San Francisco Bay, as well as the ports of Los

Angeles and Long Beach, and in the Santa Barbara Channel last December.

"There are a lot of endangered blue and humpback whales out there," said Mary Jane Schramm, spokeswoman for the Gulf of the Farallones National Marine Sanctuary. "The idea is to separate the ships from the whales. The shipping lanes are adjustable."

Gray whales are at the tail end of their northerly migration. After spending up to three months in the warm waters off Baja California, they are migrating back to Alaska.

The migration is driven by food. The seas off Alaska provide a feeding ground for the whales, but as winter approaches and days grow shorter and colder, the whales will begin their journey south to the warmer climate of Baja again. The whales are able to swim 20 hours at a time.

The blue and humpback whales target the Marin coast to eat small crustaceans called krill and will remain in the area for several months.

"It's like a big buffet table for them," Schramm said.

Contact Mark Prado via email at mprado@marinij.com

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