Electropositive shark repellent

Electropositive metals (EPMs) are a new class of shark repellent materials that produce a measurable voltage when immersed in an electrolyte. The voltages produced are as high as 1.75 eVDC in seawater. 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 on the alloy or metal utilized and its thickness, the electropositive repellent effect lasts up to 48 hours. The reaction of the electropositive metal in seawater produces hydrogen gas bubbles and an insoluble nontoxic hydroxide as a precipitate which settles downward in the water column. The precipitate is inert for repellent activity.

History

SharkDefense made the discovery of electrochemical shark repellent effects on May 1, 2006 at South Bimini, Bahamas at the Bimini Biological Field Station. An electropositive metal, which was a component of a permanent magnet, was chosen as an experimental control for a tonic immobility experiment by Eric Stroud using a juvenile lemon shark ("N. brevirostris"). It was anticipated that this metal would produce no effect, since it was not ferromagnetic. However, a violent rousing response was observed when the metal was brought within 50cm of the shark’s nose. The experiment was repeated with three other juvenile lemon sharks and two other juvenile nurse sharks ("G. cirratum"), and care was taken to eliminate all stray metal objects in the testing site. Dr. Patrick Rice, Michael Herrmann, and Eric Stroud were present at this first trial.

Mike Rowe, from Discovery Channel’s Dirty Jobs series, subsequently witnessed and participated in a test using an electropositive metal within 24 hours after the discovery. See HowStuffWorks for the video of this event ( [http://videos.howstuffworks.com/discovery/6781-best-of-shark-week-jobs-that-bite-video.htm] )

In the next three months, a variety of transition metals, lanthanides, poor metals, metalloids, and non-metal samples were screened for rousing activity using the tonic immobility bioassay in juvenile lemon sharks and juvenile nurse sharks. All behaviors were scored from 0 to 4 depending on the response. It was determined that Group I, II, III, and Lanthanide metals all produced rousing responses, but the average score generally increased with electropositivity. [AES 2007 Abstract: The Use of Highly Electropositive Metals as Shark Repellents. Eric Stroud, Patrick Rice, Craig O'Connell, Samuel Gruber]

Further testing using salt bridge electrochemical cells were conducted during 2006 and 2007 at the Oak Ridge Shark Lab. Using seawater as the electrolyte and a shark fin clipping as the cathode, voltages measured closely correlated with the standard reduction potential of the metal under test. SharkDefense now hypothesizes that a net positive charge from the cations produced by the electropositive metals accumulate on the electronegative skin of the shark. The net increase of the charge on the shark’s skin is perceived by the ampullae of Lorenzini, and above 1.2 eV potential, aversion is produced.

Electropositive metals are reducing agents and liberate hydrogen gas in seawater via hydrolysis, producing a half-cell voltage of about -0.86eV. Simultaneously, an insoluble metal hydroxide precipitate is produced, which is inert for shark repellent activity. As such, metal is lost to corrosion in the process of generating cations. SharkDefense conducted corrosion loss studies in 2008 at South Bimini, Bahamas, and found that a 70 gram piece of a custom electropositive alloy retained more than 50% of its original weight after 70 hours of immersion. Losses due to corrosion are heavily a function of temperature, therefore, the cold seawater at fishing depths serves to reduce the corrosion rate. [AES 2008 Abstract: Advances in Shark Repellent Research Using Highly Electropositive Metals. Eric Stroud, Patrick Rice, Craig O'Connell, Samuel Gruber]

Testing

Stoner and Kaimmer (2008) ["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.] reported success using Cerium mischmetal and Pacific spiny dogfish ("S. acanthias") in captivity, both with tonic immobility and feeding preference tests. Lead metal was used as a control. Encouraged by the results, a longline study was conducted off of Homer, Alaska in late 2007 with the cooperation of the International Pacific Halibut Commission. Again, lead was used as a control. This study found a 17% reduction in Pacific spiny dogfish catch, and a 48% reduction in clearnose skate catch.

However, Tallack et al. reported that cerium mischmetal was entirely ineffective [Tallack, M.S.L & J. Mandelman, (in prep). Do rare earth metals deter spiny dogfish? A feasibility study on the use of Mischmetals to reduce dogfish catches in hook and lobster gear in Gulf of Maine.] against Atlantic spiny dogfish ("S. acanthias") in the Gulf of Maine. Mandelman et al. reported that the repellent effect disappeared after starvation using captive Atlantic spiny dogfish ("S. acanthias"), and that a species-specific variation in response to the mischmetals exist between captive Atlantic spiny dogfish and dusky smoothhounds ("Mustelis canis"). [AES 2008 Abstract: The Shifting Baseline of Threshold Feeding Responses to Electropositive Metal Deterrents in Two Species of Dogfish. John Mandelman, Michael Stratton, Michael Tlusty, Shelly Tallack, Tom Fisher, Cheryl Harary, Nils Wernerfelt]

Stroud (SharkDefense, 2006) and Fisher (VIMS) observed captive cow-nose rays ("R. bonasus") changing swim elevation and ignoring blue crab baits in cages that contained neodymium-praseodymium mischmetal. The position of the treatment cages were alternated, and all cages were placed in the swim path of the rays.

Brill et al. (2008) reported that captive juvenile sandbar sharks ("C. plumbeus") maintained a 50-60cm clearance in their swimming patterns when a piece of neodymium-praseodymium mischmetal was placed in the tank.

Wang, Swimmer, and Laughton (2007) reported aversive responses to neodymium-praseodymium mischmetals placed near baits offered to adult Galapagos ("C. galapagensis") and Sandbar ("C. plumbeus") sharks on bamboo poles in Hawaii.

Present Research

As of July 2008, Dr. Richard Brill of NMFS/VIMS and SharkDefense are both conducting more at-sea trials with electropositive metals in an effort to reduce shark bycatch in commercial fisheries. As of August 2, 2008, Dr. Brill reported nearly a 3:1 reduction in sandbar shark("C. plumbeus") catch when plastic decoys were compared to metals. A high statistical signficance was obtained, as reported in the [http://hamptonroads.com/2008/08/shark-repellent-matter-life-and-death-sharks Virginian-Pilot] by Joanne Kimberlin. Recently, SharkDefense has developed a simple on-hook treatment and a bait attactment which are testing candidates on Atlantic longlining vessels during 3Q and 4Q2008.

Selectivity

As expected, teleosts are not repelled by the electropositive metal’s cation liberation in seawater. This is because teleosts (bony fish) lack the ampullae of Lorenzini. Teleost response was confirmed using captive Cobia ("R. canadum") and Pacific halibut ("H. stenolepis"). In July 2008, swordfish ("X. gladius") catch was reported on experimental hooks treated with electropositive metal.

Limitations

As with all shark repellents, 100% effectiveness will not be achieved with electropositive metals. The metals are particularly effective when the shark is relying on its electrosense. It is likely that that eletropositive metals are ineffective for deliberately-stimulated (chummed) sharks, competitively feeding sharks, and shark "frenzies". The metals are very useful in the environment of commercial fisheries, and possibly recreational and artisanal fisheries.

Sources

A mechanically hardened, slower-corroding electropositive metal alloy is now available from repelsharks.com in cut and ingot form. In 2008, Repelsharks.com was granted the exclusive license to sell electropositive metal shark repellents by SharkDefense.