Public Lecture Series
Speaker:
Richard Brill, Ph.D.
Director Cooperative Marine Education and Research Program,
Northeast Fisheries Science Center -
Virginia Institute of Marine Science
The repulsive and feeding deterrent effects of electropositive metals on juvenile sandbar sharks (Carcharhinus plumbeus)
Tuesday, April 14th, 2009
7 pm
Kingsbury Hall - N101, University of New Hampshire
directions to UNH - campus map
Abstract:
It is not uncommon for the number of shar k s caught in pelagic longline fisheries to exceed that of the targeted tunas and swordfish. Shar k populations are especially vulnerable to high rates of fishing mortality because of their slow growth rates, low reproductive output, and late sexual maturity. S calloped hammerhead, oceanic whitetip, and tiger shar k populations have already decreased by as much as 60% to 99% from their historical biomass and these species are now included on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Reduction of both shar k bycatch and depredation (i.e., shar k damage to longline gear, bait, and targeted fish species) is considered a priority.
Shar k s possess a unique sensory system (ampullae of Lorenzini) that can detect electric field gradients as small as 5 nV cm -1 and which can guide them to prey in the absence of other sensory stimuli. It should be possible, therefore, to develop effective deterrent procedures that ta k e advantage of shar k s' electroreceptive sense. Electropositive metals (which generate an electrical field when reacting with water) have been shown to rouse juvenile lemon, nurse, and spiny dogfish shar k s when brought close to their heads, and to deter spiny dogfish shar k s from attac k ing baits in a tan k study. This project was designed to determine if electropositive metals affect the behaviors of juvenile sandbar shar k s under both laboratory and field conditions. Sandbar shar k s are highly suitable for this line of research because they are closely related to many of the shar k species frequently interacting with pelagic longline gear.
Electropositive metal deterred feeding in groups of juvenile sandbar shar k s and altered the swimming patterns of individuals in the absence of food motivation (individuals generally avoided approaching electropositive metal closer than ˜ 100 cm). The former effect was relatively short-lived however, apparently due to social facilitation of feeding. In field trials with bottom longline gear, electropositive metal placed within ˜ 10 cm of the hoo k s reduced the catch of sandbar shar k s by approximately two thirds, compared to that on hoo k s in proximity to plastic pieces of similar dimensions. Electropositive metals therefore appear to have the potential to reduce shar k interactions in pelagic longline fisheries, although optimal mass, shape, composition, distance to baited hoo k s, etc. remain to be determined.
