Shark-repelling fishing gear in the works

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Shark-repelling fishing gear in the works
mongabay.com
April 23, 2008

Fishing gear that produces an electric field in sea water could help prevent sharks from becoming accidental bycatch, say scientists at NOAA.

Introducing palladium neodymium, an electropositive alloy, to a tank full of juvenile sandbar sharks "clearly altered the swimming patterns of individual animals and temporarily deterred feeding in groups of sharks," according to NOAA.

The researchers speculate that the metal "overloads" the shark's electroreceptive system which it relies upon for locating prey.

"Individual sandbar sharks would generally not approach the metal ingots closer than about 24 inches, nor attack pieces of cut bait suspended within approximately 12 inches," said Richard Brill, a research scientist at NOAA's Northeast Fisheries Science Center and head of the Cooperative Marine Education and Research (CMER) Program at the Virginia Institute of Marine Science. "This study clearly shows the alloy has the potential to repel sharks from pelagic longline fishing gear so they are not caught as bycatch, but the optimal size and shape of the alloy and other factors needs to be determined. This is a promising step."

"Our results were very promising but need further study," Brill added. "The alloy we used, palladium neodymium, appears to be a good alternative to more expensive metals. It is also machinable and is reasonably resistant to corrosion in seawater. How long the metal will last before corroding and how long it will repel sharks in the field, however, needs to be determined."

An estimated 11 to 13 million sharks are caught as bycatch each year. Several times that many — 26-73 million according to a recent study — are killed for their fins. Shark fin is a popular delicacy in Asia -- especially China, where it is typically served in shark fin soup weddings, business dinners, and other celebrations. Fins are usually sliced off as the shark, often while still alive, which is then thrown back into the ocean.

Scientists are concerned that given the low growth and reproductive rates of many species, shark populations may be slow to recover from overfishing and losses due to bycatch. Further, the decline in some shark populations is having wider ecological consequences. A study published in the journal Science last year showed that overfishing of large sharks is reducing the abundance of shellfish off the Atlantic coast of the United States.

Last week the U.S. Fisheries Service ruled that fishermen will now be required to bring shark catches to shore with fins still attached. The measure takes aim at the practice of finning.

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