Electropositive metal doesn’t scare hungry Greenland sharks

In Greenland, the longline fishery targeting halibut (Reinhardtius hippoglossoides) is plagued by a substantial bycatch of Greenland sharks (Somniosus microcephalus). This has led to a bounty for shark hearts as proof of their elimination. We went to Greenland in May to test if electropositive (EP) metals in close proximity to baited hooks could be used as a shark deterrent, an approach that we successfully used on sandbar sharks in Virginia. Although there was still a foot of snow on the ground and pack- ice choked the harbors, we were still able to push out through the ice chunks to set longlines in open waters. During the two weeks there we set 40 longlines (410 hooks) and caught 25 sharks. Unfortunately, the presence of EP metal above a baited hook did not appear to generate enough of an electric field to deter Greenland sharks, as we caught just as many sharks on EP equipped hooks as with hooks with pieces of plastic (visual controls). While this is a bit of a disappointment it is not a complete surprise as it has been reported to be ineffective with spiny dogfish and various species of rays.

We came away from this experience with a great deal of respect for these very large, but docile creatures. Although their teeth are very small, the dermal denticles on their skin are widely separated and stick straight up much like the surface of a wood rasp. The day I inadvertently handled a shark on the longline without my gloves on, I lacerated the back of my hand just by brushing against the skin.

In addition to the EP metal trials, we deployed four pop-up satellite tags and took tissue samples for age analysis. Results should be available soon, so stay tuned.