False killer whales in danger of extinction from getting caught in fishing gear

Entanglements between fishing gear and offshore false killer whales have occurred in Hawaii so often that the population has been designated a “strategic stock” under the Marine Mammal Protection Act. In response, a team of researchers and fishermen coordinated an effort along with Scripps Institution of Oceanography at the University of California San Diego in order to observe how these marine mammals interact with fishing lines.

This led to the first observation of how Hawaiian false killer whales attempt to remove fish from longline fishing gear, in a process called “depredation.” The major component of a false killer whale’s diet is gamefish, such as yellowfin tuna and mahi-mahi. In their hunt for these fish, they forage in the same open-ocean regions where commercial fishermen set 30-60 kilometer-long fishing lines in an effort to catch the same fish.

Unfortunately, while fishing in the same areas, these whales often end up as an unintended catch of the fishermen. Their designation by the Marine Mammal Protection Act as a “strategic stock” has led to a federal take-reduction strategy for reducing the negative impact to the population from the commercial fishing operations.

Researchers are interested in learning more about the animals’ behavior, as well as what attracts them to the fishing gear and how they attempt to remove the bait. To observe how the false killer whales interact with these longlines, the Alaskan and Hawaiian research team deployed an underwater camera, sound recorder, and vibration detector on longline fishing gear.

During a 30-second encounter caught on video, the scientists found that a false killer whale was producing distinct clicks and whistles as it approached the longlines and took baitfish off the hook. Researchers were able to estimate how far away the animal was from the line by calculating the vibrations on the line and how loud the whale’s sounds were.

In a paper published in the Journal of the Acoustical Society of America, lead author Aaron Thode said, “This study addresses some important questions about the nature of this depredation, and whether underwater sound can be used to study or possibly alleviate the issue.”

He believes that further studies might be able to help them understand even more about the behavior of these whales. New information could potentially be used by fishermen to hear the animals make echolocation noises before they deploy their fishing gear. Thode continued, “The study can also be helpful in designing future experiments to estimate the actual number of animals in the region.”

In the future, the research team hopes that these studies can lead to the production of a so-called “smart hook,” which could reduce the negative impacts to animals and fishing operations.

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Credit: Earth.com author Connor Ertz