Barry Peters/Wikimedia; (inset) Melanie Hutchinson

ScienceShot: Keeping Hammerheads Out of the Haul

Special fishing weights could take a bite out of endangered hammerhead shark deaths. The global population of these distinctive sharks has fallen by about 89% in the last 2 decades, largely due to illegal poaching and accidental fishing bycatch. But now, scientists have come up with a shocking way to reduce this collateral damage: generating a mild 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 in murky nearshore waters. So to help save the sharks, marine biologists took advantage of this, attaching pieces of rare-earth lanthanide metals—specifically, neodymium and praseodymium—to longline fishing gear in place of typical lead weights. The lanthanides produce an electric field in water that seemed to repel the sharks, the team reports this month in Fisheries Research. Test lines in Hawaii caught less than half as many endangered scalloped hammerhead (Sphyrna lewini) pups as lines without the metals, the researchers report. Open ocean shark species, which appear to rely on other senses to find prey, were not affected, they found. And at least for some commonly fished species including halibut and tuna, the electric fields didn't impact catch rates. The strategy could help preserve hammerhead sharks in many coastal fisheries—but there is a downside, the researchers note. Lanthanide metals are costly and difficult to work with, and as they dissolve relatively quickly in water, the weights would need to be replaced periodically by fishers.

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