Shark-repellent metal alloys are used in commercial, recreational, and artisinal fisheries to reduce the amount of unintended shark catch (shark bycatch). When tuna and swordfish are targeted, sharks are also captured and present handling problems and damage to gear. More hooks occupied by sharks means less hooks available for the targeted species. The metal alloy is placed as close as possible to the bait. Since the metal alloy is specific to the electrical sense in sharks, bony fish are not repelled, thus, the metal alloys are a shark bycatch reduction device.
Shark-repellent alloys, or electropositive metals (EPMs), are a new class of shark repellent materials that produce a voltage when immersed in seawater. The voltages produced are as high as 1.75 VDC relative to a shark skin electrode in a seawater electrolyte at pH 8.1 and standard conditions. It is hypothesized that this voltage overwhelms with ampullary organ in sharks, producing a repellent action. Since bony fish lack the ampullary organ, the repellent is selective to sharks and rays. The process is electrochemical, meaning, no power input in the form of batteries or line power is required. As chemical “work” is being done, the metal is given up in the form of corrosion. Depending of the alloy or metal utilized and their thickness, the electropositive repellent lasts up to 48 hours continously submerged in seawater.
Reseachers at SharkDefense Technologies LLC discovered the shark-repelling effects of electropositive metals in seawater on 01-May-2006 at South Bimini, Bahamas. Since that time, our research efforts have been focused on quantifying behavioral responses to various pure metals and alloys, understanding the electrochemical and corrosion processes involved, and improving gear design with respect to incorporating these metals onto circle hooks. Initial repellent findings were presented by SharkDefense at the 2006 Sea Turtle and Pelagic Fish Sensory Physiology Workshop , the 2007 American Elasmobranch Society (AES) / Joint Meeting of Ichthyologists and Herpetologists in St. Louis, MO, and the Shark Deterrent and Incidental Capture Workshop at the New England Aquarium, April 11, 2008. These metals are constituents of natural seawater. An extensive literature search revealed no toxicity issues, and the metals used are not cited as toxic/poisonous or restricted compounds.
As of 2007, SharkDefense is collaborating with NOAA, NMFS, and other fisheries scientists to validate and promote the use of these metals as a shark bycatch reduction technology. Please refer to the following publications: “Reducing elasmobranch bycatch: Laboratory investigation of rare earth metal and magnetic deterrents with sping dogfish and Pacific halibut” . Stoner, Allan W. and Kaimmer, Stephen M. Fisheries Research, 2008, AND, Brill, R., Bushnell, P., Smith, L., Speaks, C., Sundaram, R., Stroud, E., Wang, J. 2009. The repulsive and feeding deterrent effects of electropositive metals on juvenile sandbar sharks (Carcharhinus plumbeus). Fisheries Bulletin. FB-3298, AND, “Field investigation of rare-earth metal as a deterrent to spiny dogfish in the Pacific halibut fishery”, Kaimmer, Stephen and Stoner, Allan W. Fisheries Research Volume 94, Issue 1, October 2008, Pages 43-47.
Since electropositive metals represent the latest technology in shark repellent research, much remains to be studied and learned. Species-specific behavioral differences, particularly for dogfish, have already been made. These observations will provide valuable insight to future shark repellent research. Below, please find a summary of the testing performed with electropositive metals (successes, failures, publications, and press) to date, which will be updated frequently.
- (M1V MPEG) Bat ray turning 180 degrees near metal alloy (suspended at center). Courtesy Allan Stoner, NMFS
- (M1V MPEG) Broadnose Seven-Gill shark and Leopard shar turning 90 degrees near metal alloy (suspended at center). Courtesy Allan Stoner, NMFS
- (WMV) Galapagos sharks avoiding bait near metal alloy – Courtesy John Wang, NOAA
- (WMV) Galapagos shark eating bait – NO ALLOY PRESENT – NOT PROTECTED – Courtesy John Wang, NOAA
- (M1V MPEG) Leopard shark and sping dogfish turning away from metal alloy (suspended at center). Courtesy Allan Stoner, NMFS
- (WMV) Immobilized lemon shark responding to the metal alloy AND ANOTHER (WMV) Immobilized lemon shark responding to the metal alloy
- Immobilized nurse shark responding to the metal alloy – Blinder removes visual clue
- (WMV) Immobilized nurse shark – Control test with moving hand, NO ALLOY PRESENT
Species Responding Favorably
Species Not Responsive