Magnets on Fish Traps Help Limit Accidental Shark Fishing, Study Says

Magnets may be the answer to repelling sharks and rays from fish traps, according to a new study by researchers at the University of Newcastle in Australia.

The declining population of sharks and rays, also known as elasmobranchs, has been due in part to their getting accidently trapped in fisheries' catches. Looking to solve the problem, researchers at the School of Environmental and Life Sciences at the University of Newcastle experimented with various deterrents over the course of eight months. They found that the most effective tool was a series of magnets attached to traps, which increased the amount of fish caught by 30 percent and reduced the number of sharks and rays caught by the same number.

The authors of the study, which was recently published in Fisheries Journal, called their findings a "win-win" for the environment and for commercial fishermen.

They used more than 1,000 fish for the study, focusing on areas where sharks made up more than 10 percent of the total catch. Fish traps were split into three equal groups of 12. One group was fitted with magnets and another with metal bars, while the final 12 traps were left unchanged. The magnets had the biggest impact in tackling the problem.

A red snapper sits in a basket after it was caught on a tagging trip. Red snappers were the target fish in some of the fisheries accidentally catching sharks. REUTERs

Sharks get caught in traps because they have sensory pores near their nose and head that sense electrical fields. Fish create small electrical fields as they move in the ocean.The large electrical field created with the help of the magnet kept most sharks from approaching the fish traps and did not traumatize the sharks or the fish caught inadvertently in the process. Magnets also helped to limit the damage to the fish that were accidentally caught and released back into the water.

“The stress from being out of the water and handled are likely to have repercussions that will last for a period of time after they are released. The trauma may impact their energy levels and desire to feed, which can be lethal in the short-term,” said lead researcher Vincent Raoult in a statement.

Raoult also said the solution would be relatively affordable, depending on the size of the trap. “At just $2 per magnet, a trap can be fitted out for under $30, depending on the number of entrances on the trap. They simply need to be made waterproof with some epoxy to keep them from corroding,” he said.