Endangered blue whale found on Point Reyes beach likely killed by ship strike

Scientists confirmed Tuesday that the 62-foot juvenile female blue whale that washed ashore in Point Reyes died due to blunt force trauma from injuries consistent with a vessel collision. Scientists confirmed Tuesday that the 62-foot juvenile female blue whale that washed ashore in Point Reyes died due to blunt force trauma from injuries consistent with a vessel collision. Photo: The Marine Mammal Center Photo: The Marine Mammal Center Image 1 of / 15 Caption Close Endangered blue whale found on Point Reyes beach likely killed by ship strike 1 / 15 Back to Gallery

A collision with a ship is likely to blame for the death of a blue whale that washed up on a Point Reyes beach Monday afternoon.

The whale was first spotted Saturday near the Farallon Islands by a whale watching tour group. Pictures showed the blue whale stomach extremely bloated as seagulls scavenged the animal's remains. Two days later, the carcass washed up south of Limantour Beach, where scientists were able to examine the 62-foot juvenile female.

They found the blue whale had a severed spine and bruising to its ribs and jaw. The Marine Mammal Center said injuries of those kind were likely caused by a ship collision.

The necropsy was conducted by scientists from the Marine Mammal Center, California Academy of Sciences, Point Reyes National Seashore and the National Oceanic and Atmospheric Administration (NOAA).

"Blue whales are the largest animal on earth and an endangered species, so to learn that this individual's death is a result of a ship strike is particularly unfortunate," said Barbie Halaska, a researcher at The Marine Mammal Center, in a statement.

Ship strikes kill an estimated 18 blue whales each year off the West Coast according to some researchers, despite measures to reduce the impact. Voluntary programs including paying shipping companies to reduce speed while transiting through areas with large whale populations, and shifting shipping routes farther offshore have been proposed. Ships entering the San Francisco Bay must still cross the migration routes directly, and NOAA studies have found reducing speed to be the most effective at reducing the risk. In 2013, shipping lanes were narrowed to make it easier to alert pilots to whales in their path.

Discovering a whale specimen like this is still a rare opportunity to understand how a ship strike kills a whale. This is only the 10th blue whale the Marine Mammal Center has examined in 43 years.

The center collected tissue to study while the California Academy of Sciences collected its pelvic, rib and scapula bones. The rest of the whale will be left where it was found on the beach to decompose naturally.

"Understanding and documenting the extent of the injuries through a necropsy allows us to share this information with decision-makers to help find solutions to prevent these incidents in the future."

In the past two months, four other whales have washed up on Bay Area shores, from the Oakland Estuary to Marin County. The cause of death in all cases were determined to be human-related. Three were likely killed by collisions with ships and one was found severely entangled.

Read Alix Martichoux's latest stories and send her news tips at amartichoux@sfchronicle.com.