NOAA Fisheries Pacific Island Fisheries Science Center, Honolulu, Hawaii
NOAA Fisheries conducted experiments to test the ability of electropositive metals to deter sharks from feeding on baitfish. Utilizing a shark viewing cage (Figure 1), we are able to film and observe choice experiments. Galapagos sharks (Carcharhinus galapagensis) and sandbar sharks ( Carcharhinus plumbeus) were the most commonly observed sharks in the area. Results indicate that bait associated with lead metal was eaten over bait associated with electropositive metal (Figure 2 and Video 1). In addition, sharks exhibited more aversion behaviors as they approached bait associated with the electropositive metal (Video 2). These results suggest that electropositive metals do influence feeding behavior in sharks.
In conducting these experiments, NOAA Fisheries developed an assay to examine potential shark deterrent strategies that could be potentially useful in reducing the incidental capture of sharks in a fisheries setting. Experiments with an alloy of electropositive metals (Pr and Nd) indicate that the metal deters feeding and may be useful in reducing shark interactions with longline gear.
The incidental capture of sharks and rays is estimated at over 1,000,000 metric tons annually (approximately 40 million individual animals). In several fisheries, it is common to have rates of shark bycatch exceed the capture rates of targeted fish species. The problem of shark and ray incidental capture is a major concern, in particular, due to their importance as predators at the top of the marine food chain. Removal of these predators not only affects the population structure of shark and ray species, but also indirectly affects the larger marine communities.