ontrolled laboratory conditions. If repulsion occurs consistently in the lab, the next step would be to conduct field trials.
Brill says juvenile sandbar sharks were used in the study because they are readily available in the estuaries along Virginias coast, do well in captivity, feed easily, and their constant forward motion makes it easy to measure changes in their swimming patterns. They are good models for the species of sharks that are a significant problem in pelagic or open ocean longline fisheries worldwide.
An estimated 11 to 13 million sharks are caught worldwide as bycatch each year, sometimes more than the targeted fish species. Sharks, part of the taxonomic group known as elasmobranchs which also includes skates and rays, generally have slow growth and reproductive rates and late sexual maturity. These factors result in an inability of shark populations to support high rates of fishing mortality, or slow population recovery. There is concern among scientists and fishery resource managers that severe reductions in elasmobranch populations could restructure marine ecosystems.
The sandbar shark, Carcharhinus plumbeus, is one of the largest coastal sharks in the world and can reach lengths of eight feet and weigh as much as 200 pounds. Sandbar sharks are usually found in shallow coastal waters including bays and estuaries in tropical and temperate waters around the world. In the western Atlantic Ocean they range from Massachusetts to Brazil, with the waters of the lower Chesapeake Bay considered a major nursery ground. Humans are their main predator.
Our results were very promising but need further study, Brill said. 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.
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| Contact: Shelley Dawicki shelley.dawicki@noaa.gov 508-495-2378 NOAA National Marine Fisheries Service Source:Eurekalert |
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