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Press Release

Ship Strike Kills Gray Whale in San Francisco Bay Area; Three Others Dead Under Ongoing Investigation

April 9, 2021
  • Behavior
  • Species conservation
  • Pathology

The Marine Mammal Center investigates four gray whale deaths in the SF Bay Area since last Wednesday, confirming ongoing challenges faced by the hard-hit species

A team of scientists from The Marine Mammal Center, the world’s largest marine mammal hospital, investigated the deaths of two gray whales Thursday afternoon in the San Francisco Bay Area and confirmed one died due to ship strike. By investigating deaths like this, the Center can identify and respond to rapidly changing environmental trends as well as human impacts on marine mammal populations.

“It’s alarming to respond to four dead gray whales in just over a week because it really puts into perspective the current challenges faced by this species,” says Dr. Pádraig Duignan, Director of Pathology at The Marine Mammal Center. 

These necropsies are critical to provide insights into gray whale population health and that of their ocean home, including how human activity impacts them.

Malnutrition, entanglement, and trauma from ship strikes have been the most common causes of death found by the Center’s research team in recent years. The Center’s researchers are studying the locations and behaviors of whales in the San Francisco Bay so that informed decisions can be made to better protect whales. Public funding and support for this investigatory work is essential.

The Center’s experts along with partners at California Academy of Sciences performed necropsies, or animal autopsies, on whales found separately at Angel Island State Park and Muir Beach. During the necropsy at Muir Beach, scientists discovered significant bruising and hemorrhaging to muscle around the whale’s jaw and neck vertebrae consistent with blunt force trauma due to ship strike. 

The team identified the gray whale as a 41-foot adult female that was minimally decomposed based on the quality of the internal organs. Experts also noted the whale was in good body condition based on the blubber layer and internal fat levels.

At Angel Island State Park, the team investigated a 37-foot subadult male gray whale that was moderately decomposed based on the quality of the internal organs. During the investigation, scientists noted the whale was in average body condition based on the blubber and body fat levels. There was no initial evidence of trauma or infectious disease. Experts plan to reexamine the whale’s skeleton at a future date to completely rule out human interaction.

“Our team hasn’t responded to this number of dead gray whales in such a short span since 2019 when we performed a startling 13 necropsies in the San Francisco Bay Area,” says Dr. Duignan. 

Gray whales are ocean sentinels due to their adaptability and foraging habits, meaning they have a lot to tell us about the health of the ocean, so to see the species continue to suffer with the added threats of human interaction is a major cause for concern.

Biologists have observed gray whales in poor body condition during their annual migration since 2019, when an Unusual Mortality Event was declared by the National Oceanic and Atmospheric Administration (NOAA). Increased numbers of gray whales have since been sighted in the San Francisco Bay, including multiple individuals in early April, as the population continues their northerly migration to cool, food-rich Arctic waters. The Center serves as an investigator on NOAA’s Unusual Mortality Event Working Group for gray whales.

Climate change affects water temperatures and prey availability, leading to shifting food sources for marine mammal populations and other marine species. Overfishing can also lead to reduced prey availability. Effective policies are critical to protect vulnerable marine mammal populations from the many human-caused threats they face in the wild.

According to NOAA, nearly one in four gray whales migrating along the U.S. West Coast has died since the last recorded population assessment in 2015 and 2016. This drop in the gray whale population is similar to the last Unusual Mortality Event that took place from 1999-2000 but the current loss could be even greater due to limited aerial and boat survey capabilities due to the ongoing pandemic.

The Center’s experts were first notified of a dead gray whale in San Francisco Bay by the United States Coast Guard. The whale was eventually located in the Berkeley Marina area and safely towed to Angel Island State Park by a private towing company. 

The Center first received reports Thursday morning of the dead whale at Muir Beach from a park ranger at Golden Gate National Recreation Area. The Center collected tissue samples during both necropsies to contribute to baseline data and various research studies. The California Academy of Sciences archived both whale’s pelvic bones and baleen samples for their scientific collection.

As an essential nonprofit organization operating during the ongoing pandemic, the Center and its partners are currently deploying response teams with fewer personnel for shorter durations and with increased personal protective equipment to safely continue this important work. This necessary action has led to a decrease in data and sample collection during necropsies, which can make it more difficult to determine why a whale may have washed ashore.

The public can play an important role in the conservation of gray whales and other whale species by reporting whale sightings.

To report a dead whale or whale in distress, call the Center’s rescue hotline at 415-289-SEAL (7325).

Gray Whale Necropsies in 2021

April 1, 2021: adult female gray whale; Angel Island State Park via San Francisco Bay (Crissy Field); Cause of death: undetermined

April 3, 2021: adult female gray whale; Fitzgerald Marine Reserve, San Mateo County; Cause of death: suspected trauma due to ship strike

April 8, 2021: subadult male gray whale; Angel Island State Park via San Francisco Bay (Berkeley Marina); Cause of death: undetermined

April 8, 2021: adult female gray whale; Muir Beach; Cause of death: trauma due to ship strike

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