Two dead gray whales in San Francisco Bay spur investigation

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Two dead gray whales — one that died of severe malnutrition
and the other of undetermined causes — were found floating in the
San Francisco Bay this week, launching a scientific investigation
into why.

Experts from the Marine Mammal Center and its partners at the
California Academy of Sciences conducted necropsies on the whales,
but were unable to perform a full examination on the second whale
because of unsafe conditions. Both whales are believed to have been
female, about 1 year old and 23 feet long.

The necropsies — animal versions of an autopsy — were
conducted on one whale on the shores of Angel Island on Tuesday.
Experts determined that the whale had suffered from severe
malnutrition. They found a significant lack of blubber and body fat
on the whale, which is a common sign of malnutrition, and the
whale’s stomach was empty.

The second whale appeared to have sufficient blubber reserves;
scientists plan to revisit the carcass another time to gather more
evidence and attempt to determine a cause of death.

Although common causes for deaths in cetaceans range from blunt
force trauma from ship strikes to malnutrition, trauma and
entanglements, there was no evidence of trauma or infectious
disease in either whale.

Officials from the Marine Mammal Center collected tissue and
blubber samples on both whales to contribute to various research
studies, and to submit for further testing.

Gray whales make the longest migration of any cetaceans,
traveling 11,000 miles from feeding grounds in Alaska to the warmer
waters off Mexico’s Baja California and back again. They are one
of the most frequently sighted whales in California, passing along
the coast in December and January during their southern migration,
and again in April and May on their northern journey.

In recent years, biologists have found younger gray whales in
poor condition during the migrations, said Dr. Padraig Duignan,
chief research pathologist at the center, which could have
contributed to the first whale’s death.

“It’s likely that after not feeding this winter, she
didn’t have enough reserves built up to survive her journey
north,” Duignan said.

Experts have also noticed a migratory behavior change with gray
whales entering the San Francisco Bay in the late winter and early
spring months. Historically, one or two gray whales have
temporarily passed beneath the Golden Gate Bridge during this time
period, but last week, experts counted five entering the bay.

“The number of gray whales entering the San Francisco Bay this
year has been abnormally high, and they’re staying much longer
than in years past,” said Bill Keener, a whale expert at Golden
Gate Cetacean Research. “There’s likely a few factors at play
here, including food source availability and a relatively sheltered
habitat for juvenile whales that are in weaker body
condition.”

In its 44-year history, the Marine Mammal Center has responded
to more than 70 gray whales in distress. These are the first two
whale necropsies the center has completed this year. In 2018, the
center responded to five gray whale strandings, including three in
San Francisco Bay.

These dead whales were first seen Sunday and Monday, with one
floating between Tiburon and Angel Island near Raccoon Strait. The
carcass became stranded on the shoreline near Belvedere Cove late
Sunday. A second report was received Monday morning from the U.S.
Army Corps of Engineers near the Bay Bridge. The Army Corps and a
marine salvage company towed the carcasses to Angel Island on
Monday afternoon.

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Officials at Angel Island State Park authorized a landing area so
the experts could perform the necropsy.

“Each of these investigations provide an invaluable
opportunity to better understand the threats that marine mammals
face,” Duignan said. “The gray whale population along the U.S.
West Coast is a conservation success story, but the species
continues to face numerous environmental threats including
entanglements, ship strikes and shifting food availability.”

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Source: FS – All – Interesting – Lifestyle
Two dead gray whales in San Francisco Bay spur investigation