Electromagnetic fish hook reduces accidental shark catches
By Ben Coxworth
August 2, 2011
In fisheries all over the world, many fish are caught using a process known as pelagic longlining. This consists of fishing crews traveling out into the open ocean and deploying a series of baited hooks that are all attached to one horizontal main line, that can range from 20 to 40 miles (32 to 64 km) in length. After being left to sit in the water for a period of time, the line is hauled abroad a fishing vessel, where the fishes that took the bait are removed from the hooks. Unfortunately, even though they're not usually one of the targeted species, sometimes sharks will be among the fish captured. A new type of fish hook, however, is said to reduce unintended shark catches by up to 94 percent.
First of all, why wouldn't fishers want sharks on their lines?
For one thing, as apex predators that are essential to the balance of the marine ecosystem, several types of sharks are protected species - depending on the country. Sharks can also bite off the hooks, break the main line, or cause entanglements. They also occupy hooks that could have been taken by more sought-after fish, and if they're still alive when hauled aboard the boat, can injure crew members when being removed from the line. Additionally, the time spent removing sharks from the line and/or repairing the damage that they cause could be spent catching more fish.
The SMART (Selective Magnetic and Repellent-Treated) Hook, created by New Jersey-based Shark Defense, is intended to repel sharks. This is due to the fact that it is magnetic, and coated in a metal that produces an electrical current when placed in seawater. Electromagnetic fields are known to confuse sharks' sensory systems, and as such the creatures try to steer clear of them when possible. It requires no power source, and reportedly only costs slightly more than a traditional hook - an amount that should be made back through reductions in damaged equipment, wasted time, and unmarketable catches.
In a set of 50 tests using two different groups of sharks, it was found that smaller, recreational-sized SMART hooks with bait received 66 percent less shark strikes than their conventional counterparts. Larger, commercial-sized SMART hooks received 94 percent less, due to the fact that more of the shark-repellent metal was present.
Magnetic and voltage-creating metals have separately been shown to reduce shark catches by 18 to 68 percent in past studies, although the Shark Defense researchers state that combining the two properties boosts the SMART hook's repellent properties.
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