Saving the Greenland Shark
There must be a way for both fishing fleets and arctic sharks to survive.
by David James with Peter Bushnell
More than ten million sharks die each year in the world’s commercial fisheries. Eco-physiologist Peter Bushnell studies one species, the Greenland shark, not merely to understand marine biology: “The job is not to save people from sharks, but exactly the opposite, to save sharks from people.”
Peter and his colleagues Rich Brill and John Steffensen, have also been learning about the shark’s behavior by releasing sharks tagged with satellite tracking devices (PSATs), mini-computers record¬ing and storing data on water temperature, depth and light levels the sharks encounter as they swim. When a predetermined amount of time has elapsed (3-12 months) the tags separate from the shark, float to the surface, and send the stored data, as well as their current location, to satellites overhead. Since 2011 they have successfully deployed PSATs on sharks in a variety of locations in eastern and western Greenland and are beginning to piece together a better idea of how they lead their lives. For instance, it seems clear that they tend to swim very slowly, probably searching for prey near the bottom. This can take them to depths that exceed 1600m (~5300 ft) and water temperatures that are as low as -2oC (28oF). Interestingly some sharks seem to migrate significant distances (500-700 miles) during the summer while others stay where they were tagged and move very little over a nine-month period.
The conflict between Arctic fisherman and Greenland sharks illustrates in miniature the global conflict between humans and the environment. Fishing and fish processing are the vital industries in Greenland, and coastal villages there depend heavily upon fishing for survival. Fisherman use long monofilament lines hung with baited hooks to haul in catches of cod, halibut, and char. However, the bait and snared fish are irresistible to the sharks. They go for the bloody fish, get hooked on the line, and instinctively begin to thrash and roll, wrapping themselves in the lines and destroying the gear. The fishermen lose their catch, their gear, and must dispose of a Greenland shark body made up of poisonous meat that can be rendered edible only by fermenting for several months. The sharks are such a menace to fishing that some local governments in Greenland pay a bounty of $38 per shark heart to eliminate them from the seas per shark heart to eradicate them.
But Greenland sharks are more than pests to fishing. They are the world’s only species of sub-Arctic shark, endowed with physiological adaptations that allow them to live in their frigid habitat. A recent study of shark lenses conducted by Bushnell and his colleagues suggests that their lifespan may exceed 150 and 175 years, making them possibly the longest-lived vertebrate on earth. On top of that, females reach sexual maturity around age 90 and have a limited number of pups over the course of their lifetimes. If they continue to be threatened, the Greenland shark population may not be capable of rebounding fast enough to save the species from extinction.
Bushnell is dedicating his energies to solving this problem. Surely there must be a way to keep these sharks and these fishermen from becoming entangled. With funding support from National Geographic and the Save Our Seas Foundation he and his colleague Dr. Rich Brill have been experimenting with blends of electropositive metals in the hopes of developing an effective shark repellent. All sharks have electroreceptors on the skin of their faces. The electroreceptors are highly sensitive to minute electrical currents in the water, an adaptation that helps the shark detect the heart beats and muscle contractions of prey in the water and hidden in the mud. Bushnell and Brill hope to develop a metal composite that could be mounted above baited hookss, be detected by the sharks, and repell them. Last year, Peter and his research crew set out longlines strung with bait above which were mounted either electropositive metal pieces or similarly shaped plastic pieces as controls. Would the sharks be deterred by the electropositive metals, or would they go for the delicious bait?
The results of the experiment were inconclusive. Unfortunately, the electropositive materials didn’t seem to deter the sharks. Four were caught on baits with electropositive metal above them and an equal number were caught on plastic equipped hooks. However, it’s possible that the deterrent effect of the electropositive metals was not strong enough to offset the allure of the baits. The idea requires more testing. Bushnell’s future experiments in the Arctic will seek to further test this question and others about Greenland shark biology.