Science for a Blue Planet

Science for a Blue Planet

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Autopsy of a Humpback Whale

By | May 12, 2015

pacifica whale crop

Results show the Pacifica whale died from a ship strike

This past week, I helped determine the cause of death for the 42-foot female humpback whale that washed up on a Pacifica, Calif., beach. (See broadcast story.)

Led by experts from the California Academy of Sciences and the Marine Mammal Center, 10 volunteers with the Marine Mammal Stranding Network met on the beach at 7 a.m., knowing our time was limited before an early afternoon high tide. We broke off into teams to measure the whale’s total length, fluke and front flipper length, and blubber depth. Another team inspected the carcass and photographed all angles. During this initial examination, we noticed significant bruising on the left side of the animal near the tail stock.

Knowing very well the life history of these animals, losing such a valuable member of the humpback whale population was sad news to me. Humpback whales (Megaptera novaeangliae) were hunted to the brink of extinction before a moratorium was introduced in 1966. Although the whales have partially recovered, collisions with ships, entanglement in fishing gear and noise pollution continue to impact the 1,400 humpback whales living off the California coast.

Humpbacks do not reach maturity until eight to 12 years of age and can live for up to 75 years. Females typically breed every two or three years with a gestation period of 11.5 months and calves can stay with their mothers for two years. With such a long-lived, and slow to mature and reproduce species, every individual counts.

Volunteers perform the necropsy (autopsy) of the female humpback whale wahsed up near Pacifica. Photo: Ryan Berger

Volunteers perform the necropsy (autopsy) of the female humpback whale washed up near Pacifica. Photo: Ryan Berger

After finishing the photographs, we began the necropsy (autopsy) process. First, we used large knives to cut deep through the skin and blubber layer, revealing the muscle tissue. You need to keep a strong grip on the knife as it becomes covered in oil. As expected, when we peeled away the blubber from the bruised area, we documented blood-stained, necrotic muscle tissue in a localized area. Tissue damaged in such a way means the trauma took place while the animal was still living. We know this because tissue damaged while alive decomposes faster after death.

With limited time due to incoming tides, we focused our efforts on the traumatized area. Sure enough, when we cut away the necrotic muscle tissue to expose the backbone, we discovered four broken vertebrae. We felt confident in saying this whale had died as a result of blunt force trauma caused by a ship strike. We also examined contents of the abdominal and thoracic cavities to look for other potential causes of death but we found nothing remarkable.

It has been a couple days now since the necropsy and I’m finally starting to get the stench of decomposing whale off of my hands and arms. As you can imagine, my meals have been less enjoyable as I’m reminded of the events that unfolded each time I bring my hands to my face. But that certainly won’t influence my future decisions to contribute to the understanding of why these majestic animals wash up on our beaches.

This was the fifth whale to show up dead on a northern California beach in 2015. It certainly won’t be the last. In the meantime, I am proud to work for Point Blue Conservation Science and our partners to help endangered whales. We are collaborating with NOAA’s National Marine Sanctuaries to identify whale hotspots off the West Coast and provide recommendations for protection. Also, our collaborative partnership for the Whale Alert app and website is helping prevent endangered whales from being injured or killed by commercial vessel strikes in increasingly busy shipping lanes. (See previous Whale Alert blog post.)

A broken vertebrae from the whale. Photo: Ryan Berger

A broken vertebrae from the whale. Photo: Ryan Berger

I would like to thank Point Blue for allowing me to participate in the necropsy and to collaborators at California Academy of Sciences and the Marine Mammal Center who invited me to assist in such important work. Nobody wants to see these animals pass away but, in instances like this, it does provide us with the opportunity to collect scientific data that can be used in the future to save these special animals.

In Pacifica, we came away with some satisfaction as to what happened to the female humpback but all too often we walk away without conclusive evidence. This reinforces how much there is to learn about these mysterious animals that normally allow us only brief glimpses into their underwater world.

 

Ryan Berger is a Farallon Program Biologist for Point Blue Conservation Science.

Main photo: Ryan Berger

Learn more about Point Blue’s work on oceans and coasts.

 

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