A Fitbit-like device has captured the first known footage of a boat striking a basking shark, according to a new study.
The basking shark (Cetorhinus maximus), the world’s second-largest fish, is endangered due to historical overfishing and government culling programs. But sightings have increased off the coast of Ireland, where basking sharks aggregate to feed on small crustaceans at the surface, the study notes.
To understand how these sharks feed, Alexandra McInturf, a fish researcher at Oregon State University, U.S., and her colleagues had tagged a 7-meter (23-foot) female basking shark with a Fitbit-like device in April. This device had a camera and sensors to record the shark’s movements and was set to self-release in about 18 hours.
When the team analyzed the data from the device, they noticed an interesting series of events. For the first six hours, the shark fed at the surface, diving occasionally. But suddenly, a large boat cut across the shark’s back, making it tumble for a bit. Then the shark dove rapidly down to the seabed, where it remained for much of the next seven hours, when the tag released.
The researchers don’t know what happened after that. However, this is the first time scientists have directly observed a basking shark’s immediate behavioral response to a boat collision. And they could only do so thanks to the tracker, McInturf told Mongabay in an email. “These devices are costly, data-intensive and require retrieval to offload the data,” she added.
“There are a number of examples of whale sharks colliding with boats, but for basking sharks it is not well reported and in fact I am not aware of any studies reporting basking sharks colliding with boats,” David Ebert, a shark researcher at San Jose State University, U.S., who wasn’t involved in the study, told Mongabay. “It would not be unexpected since they do feed at the surface.”
It wasn’t a surprise for the study’s authors, either. “We do see sharks with anti-fouling paint on their backs in this location, indicative of brushing against a ship’s hull, as well as with scars on their fins, likely from propellers,” McInturf said.
In May, the Irish government designated its first marine national park, off the Kerry coast, where the researchers conducted their study. The researchers say the recorded collision highlights the need for more studies of basking sharks to inform policies to protect them.
“Though basking shark-specific policies have yet to be announced within the park (as far as I am aware), further action, like speed restrictions when, or at locations where, basking sharks are likely to be at the surface, would greatly help reduce the likelihood of such strikes in the future,” McInturf said.
Banner image of basking shark by Greg Skomal/NOAA Fisheries Service (Public domain).
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