Vessel strike, malnutrition likely killed whale that spent 75 days in San Francisco Bay
The adult male whale was found dead a mile offshore last Saturday before washing up on North Beach in the Point Reyes National Seashore the next day.
By Kiley Russell | Bay City News
A gray whale that died after spending at least 75 days in the San Francisco Bay was likely killed by a combination of malnutrition and trauma caused by a collision with a maritime vessel, according to officials from the Marine Mammal Center.
The adult male whale was found dead a mile offshore last Saturday before washing up on North Beach in the Point Reyes National Seashore the next day.
A necropsy performed by a team of 11 scientists from the Marine Mammal Center and the California Academy of Sciences shows the 39-foot whale was emaciated at the time of death.
It also shows that the animal was likely hit by two ships or large boats in separate collisions based on the presence of a large, slowly healing, older scar on its back, sea lice on the wound, multiple rib and spinal fractures under the scar, as well as more recent skull fractures, hemorrhaging and muscle damage to the area where the head connects to the body, according to Marine Mammal Center officials.
The second vessel strike resulted in damage akin to “severe whiplash” to a human involved in a car crash and was the likely cause of death, center officials said Thursday in a news release, which also details the results of a second whale necropsy performed at around the same time.
The body of that whale, a 37-foot adult male gray whale, was also found in the Point Reyes National Seashore on Saturday, but on the north end of Agate Beach.
Scientists couldn’t determine the cause of death for the second whale, which appeared to have died suddenly despite being “in excellent body condition,” according to Marine Mammal Center officials.
They did find that the whale had consumed plants and invertebrates it might have “scooped up from the bottom of the Bay,” where it was sighted in early May, which “supports the Center’s ongoing field observations that gray whales are feeding while inside San Francisco Bay,” according to the announcement.
The discovery of two dead whales within hours of each other “is challenging and concerning to say the least,” said Padraig Duignan, director of pathology at the Marin Headlands-based Marine Mammal Center.
“As sentinels for ocean health, gray whales face several human-caused threats including vessel strikes,” Duignan said. “This critical observation and pathology data can help build a stronger case about the current challenges this species faces and solutions to address them.”
The whales were the third and fourth found dead in the region this year.
On March 25, a necropsy determined that a subadult male gray whale found on Bolinas Beach in Marin County likely died from a vessel strike, which is also thought to be the cause of death for a juvenile male gray whale found dead at the San Leandro Marina in April.
According to the National Oceanic and Atmospheric Administration, the gray whale population in Alaska and along the West Coast is in the midst an “unusual mortality event” that seems to have started in 2019, during which there has been a 38 percent drop in the number of migrating whales.
The Marine Mammal Center also reminded people Thursday to stay away from all whales, living or dead, as they are federally protected, and to report any sightings to its website at https://www.marinemammalcenter.org/report-an-animal/whale-dolphin-sightings.
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