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What caused the 45-foot-long dead whale to wash up on San Francisco's beach

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On Sunday, June 20, a 45-foot-long gray dead whale washed ashore on San Francisco's Ocean Beach.

Until now, experts were not able to confirm the cause of death. The Marine Mammal Center scientists, the largest marine mammal hospital in the world, and the California Academy of Sciences are investigating this gray whale case. They performed a necropsy on Monday afternoon.

The necropsy done revealed the whale is a 45-foot adult female. Based on the fat stores and blubber layer, the body condition is average. Moreover, the scientists discovered, based on the quality of the skin, internal tissues, and organs, that the whale was in relatively fresh condition. Also, based on the multiple fractured spinal vertebrae but the lack of bruising and hemorrhaging to nearby tissue, the scientists believe the gray whale was probably hit a ship after it had already died of another cause.

During this time, whales migrate north to cool and for the food-rich Arctic waters. But the minimal stomach contents discovered made scientists unsure of why the whale was migrating so late this season. Moreover, gray whales don't have a calf every year and when they don't, the adult female whales migrate north early.

“Gray whales are sentinels for ocean health so performing these investigations is essential to better understand how human activity and changing environmental trends are impacting this species,” says Dr. Pádraig Duignan, Director of Pathology at The Marine Mammal Center.

Unfortunately, since April 2021, 14 dead gray whales wash up in the Bay Area. This is the highest number of dead gray whales that end up in this area since an Unusual Mortality Event was declared for the species in 2019.

The number of dead whales terrifies the scientists. The Center’s research team identified malnutrition, entanglement, and trauma from ship strikes are the most common whales' causes of death identified.

Now, the Center’s team participates as an investigator on NOAA’s gray whale UME working group. They study the factors that lead to the dead whales and the impacts from harmful algal blooms, infectious disease, natural predation, and human interactions.

"Adult females with calves are usually the last to migrate north to the summer feeding grounds in Alaska. However, this adult female did not show signs that she had recently nursed a calf,” says Moe Flannery, Senior Collections Manager of Birds and Mammals for the California Academy of Sciences. “We are hopeful that samples taken during the necropsy will shed some light on the reasons behind her late journey north and any potential ailments that may be affecting the gray whale population." - The Marine Mammal Center
The Marine Mammal Center/ Website

Since 2016, the gray whale population on the west coast has declined significantly, by 24%. At the moment, according to Noaa, there are 20,580 whales left.

According to a study done by Regina A. Guazzo, Alisa Schulman-Janiger, Michael H. Smith, Jay Barlow, Gerald L. D’Spain, Dennis B. Rimington, and John A. Hildebrand named "Gray whale migration patterns through the Southern California Bight from multi-year visual and acoustic monitoring":

Over these 7 migration seasons, the proportion of the population migrating along a nearshore route within the sighting range of visual ob- servers increased substantially, with the proportion migrating off Los Angeles increasing the most. High densities of shipping around the San Pedro Bay port complex and millions of people living and working in the metropolitan area around Los Angeles, in addition to an increasing proportion of gray whales migrating along the coast, may result in increased negative impacts from ship strikes, fishing gear entanglements, background noise, and chemical pollution. Perhaps an increasing proportion of gray whales are using the nearshore route due to an increased population with a larger proportion of younger whales that may favor more nearshore routes compared to older whales that may migrate more offshore (Sumich & Show 2011). - Study

So if whales are traveling closer to the coast, the risk is higher and this can even lead to their death.

Further studies need to be done to discover how other factors, such as climate change, affect gray wales migrations patterns and why the number of dead gray whales washes up is rising.

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