Featured Image Credit: Clark Miller via Natural History Museum
By Kira Krall
In a behavior known as depredation, fish and marine mammals steal bait off of hooks. This can become a problem when marine mammals attempt to score a free meal and end up caught in the hook and fishing line themselves, like this pregnant dolphin that was rescued from a drum line in Australia. Depredation also impacts fishermen by stealing both bait and the targeted fishery species. A research team from Scripps Institution of Oceanography at the University of California San Diego decided to survey baited hooks to get a better idea of depredation at the hands of False Killer Whales.
Hawaii has major yellowfin tuna and mahi-mahi fisheries. These predatory fish are caught in open ocean using a longline. Guess who else likes to fish in open ocean for large fish? False killer whales. The UC San Diego team deployed a microphone, video camera, and vibration detector at various points along a Hawaiian longline.
The UC San Diego team observed 30 seconds of data from all three types of recordings. The audio revealed a unique vocalization that included communication calls as well as echolocation. The vibration data clued researchers in on how far away the whales were as they plucked three fish from the baited hooks. Unique tugging patterns for different species could be revealed under further study.
While the results have yet to be analyzed, the data could help future studies in Hawaiian false killer whales like acoustic monitoring. This study could also help develop what’s called a “smart hook”, or a bycatch-free hook. Another depredation reduction method could use audio transmitters to deter marine mammals from the longlines. Only through scientific and fishery cooperation can we work toward a more sustainable ocean.