Special Fishing Weights Could Help Save Hammerhead Sharks

The new specialized fishing lines incorporate a mild induced electric field to deter sharks. Coastal shark species, such as hammerheads, rely on electrically sensitive organs in their snouts for navigation and prey detection. Credit: Barry Peters/Wikimedia; (inset) Melanie Hutchinson

The global population of hammerhead sharks, a group of sharks in the family Sphyrnidae, has plummeted by 89% in the last 20 years, largely due to illegal poaching and accidental fishing. Scientists have come up with a way to reduce the bycatch of hammerhead sharks.

The scientists published their findings in the journal Fisheries Research. The new specialized fishing lines carry a mild, induced electric field near fishing lines to keep the sharks away. Coastal shark species, like hammerheads, use electrically sensitive organs in their snouts to navigate and find prey.

A scalloped hammerhead shark (Sphyrna lewini). Credit: Flickr/Suneko

In order to save the sharks, attaching pieces of rare-earth lanthanide metals, like neodymium and praseodymium, to longline fishing gear in place of lead weights appears to repel the sharks. Test lines in Hawaii caught less than half as many endangered scalloped hammerhead shark (Sphyrna lewini) pups as lines without.

Open shark species, which use other senses to find prey, weren’t affected. And for some commonly fished species, like halibut and tuna, electric fields didn’t impact catch rates. This strategy could help preserve hammerhead sharks in coastal fisheries. However, lanthanide metals are difficult and costly to work with, and dissolve rather quickly in water. The weights would have to be replaced periodically.

Reference: “The effects of a lanthanide metal alloy on shark catch rates” by Melanie Hutchinson, John H. Wang, Yonat Swimmer, Kim Holland, Suzanne Kohin, Heidi Dewar, James Wraith, Russ Vetter, Craig Heberer and Jimmy Martinez, 20 July 2012, Fisheries Research.
DOI: 10.1016/j.fishres.2012.07.006