The carcass of a gray whale which stranded in Pacifica recently. (Courtesy photo/The Marine Mammal Center)

Ship strikes likely cause of recent gray whale deaths

A gray whale that recently stranded in Pacifica was likely struck by a ship, scientists at The Marine Mammal Center confirmed Friday.

A gray whale that recently stranded in Pacifica was likely struck by a ship, scientists at The Marine Mammal Center confirmed Friday.

The whale died from blunt force trauma that can be attributed to a ship strike, making it the second gray whale this month that scientists confirmed died due to a ship collision.

The necropsy in Pacifica, CA, was completed Wednesday afternoon by scientists from The Marine Mammal Center in Sausalito and its partners at California Academy of Sciences, according to a press release from the center.

A third necropsy completed on Thursday on a carcass found in Richmond showed that another gray whale may have been hit by a ship. Increased numbers of gray whales have been sighted in the San Francisco Bay as the population continues their northerly migration this spring.

“We’re incredibly concerned to discover the death of three gray whales due to ship strikes in two weeks,” said Dr. Padraig Duignan, Chief Research Pathologist at The Marine Mammal Center said in the release. “Investigating each death is critical so that decision-makers can advise on shipping speeds in areas where whales are known to travel.”

Center researchers completed the necropsy Thursday on a gray whale carcass that surfaced last week in Richmond. The team discovered deep propeller wounds that had severed its fluke. It was in otherwise excellent body condition, indicating it was not malnourished. Scientists suspect that this whale died due to a ship strike, and will confirm through further testing. It is also suspected that she was the mother of the calf that died due to ship strike last week. Genetic testing will be conducted to confirm this theory. The two were seen foraging near San Mateo days before the calf’s carcass surfaced.

Blunt-force trauma from ship strikes, malnutrition and entanglements are the most common causes of death in whales The Marine Mammal Center’s research team has investigated.

The Greater Farallones National Marine Sanctuary initiated a voluntary vessel slowdown program in 2012 with the U.S. Coast Guard and International Maritime Organization to help reduce the lethality of ship strikes. The program, which was first developed in response to threats to endangered whale species, has become a nationwide model of collaboration with partnering agencies and shipping companies.

“The death of seven gray whales in the San Francisco Bay Area this year is a cause for serious concern as it speaks to the broader challenges this species continues to face,” says Dr. Duignan. “The findings of these investigations are incredibly valuable as they can help policymakers find long-term environmental solutions to help prevent these incidents in the future.”

The whale in Pacifica was determined to be a 30-foot female. The whale in Richmond was a 30-foot adult female, with its fluke absent. The Center collected more than two dozen tissue and blubber samples from each whales to submit for further testing.

Biologists have observed gray whales in poor body condition during their annual migration this year potentially due to anomalous oceanographic conditions over the past few years that have contributed to shifting food sources. Malnutrition was the cause of death for three other gray whales that have stranded since March. A seventh whale carcass surfaced in Hercules, CA, and an investigation is pending.

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.

“Many of the gray whales traveling through the relative safety of our outer coast waters of the sanctuary are detouring into the dire straits of San Francisco Bay in an act of desperation,” said MaryJane Schramm, spokesperson for the National Oceanic and Atmospheric Administration’s Greater Farallones National Marine Sanctuary in the press release. “Anyone on boats and other watercraft should prevent additional stress by staying at least 300 feet away and give them every break you possibly can.”

The eastern North Pacific population of gray whales has returned from the brink of extinction thanks to protections that prevented hunting. However, all species of whales face threats such as ship strikes, entanglements and shifting food availability, so it is critical for the Center to investigate each death in order to better understand the scope of human impacts on these animals.

Scientists at The Marine Mammal Center have responded to more than 80 gray whales in the organization’s 44-year history.

How you can help:

– Report sick and injured marine mammals to The Marine Mammal Center by calling 415-289-SEAL (7325).

– Maintain a safe distance of at least 50 feet from a stranded cetacean and keep dogs away.

– The Marine Mammal Center is a nonprofit and depends on donations from members of the public to respond to and care for marine mammals and conduct research.

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