January 13, 2023 — The ocean can be a dangerous place, even for a shark. Despite sitting at the top of the food chain, these predators are now reeling from destructive human activities like overfishing, pollution and climate change.
Researchers at UC Santa Barbara focused on a particularly troublesome issue for sharks: tangles with the longline tuna fishery. Using data from regional fisheries management organizations and machine learning algorithms, the scientists were able to map out hotspots where shark species face the greatest threat from longline fishing. The findings, published in Frontiers in Marine Science, highlight key regions where sharks can be protected with minimal impact on tuna fisheries.
Offshore longline fisheries take an especially heavy toll on ocean life. The non-selective technique has the highest rate of shark bycatch. “Longline fishing gear is exactly what it sounds like: a long line with lots of hooks attached to it that are baited. And they can be left in the water, waiting for fish to bite, for a very long time,” explained co-lead author Darcy Bradley, who heads UC Santa Barbara’s Ocean & Fisheries Program at the Environmental Markets Lab (emLab). These baited hooks catch predators like tuna, but many nearby sharks will also converge on the bait.
Rather than simply report how many sharks were caught and where, the authors aimed to assess the relative risk sharks faced across different areas of the ocean. “One of the main questions was ‘Where is the risk for catching sharks the highest, and does that overlap with fishing effort?'” said co-lead author Echelle Burns, a project scientist at emLab.