Electropositive metal
Encyclopedia
Electropositive metals are a new class of shark repellent
materials that produce a measurable voltage
when immersed in an electrolyte
such as seawater
. The voltages produced are as high as 1.75 VDC in seawater. It is hypothesized that this voltage overwhelms the 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, so no external power input is required. As chemical work is done, the metal is lost 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.
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
(Negaprion 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 shark
s (Ginglymostoma 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.
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.
and Pacific spiny dogfish
(Squalus acanthias, a type of shark) 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 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 against Atlantic spiny dogfish in the Gulf of Maine
. Mandelman et al. reported that the repellent effect disappeared after starvation using captive Atlantic spiny dogfish, and that a species-specific variation in response to the mischmetals exist between captive Atlantic spiny dogfish and dusky smoothhounds (Mustelis canis).
Stroud (SharkDefense, 2006) and Fisher (VIMS) observed captive cownose ray
s (Rhinoptera 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 shark
s (Carcharhinus 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 sharks on bamboo poles in Hawaii.
(C. plumbeus) catch when plastic decoys were compared to metals. A high statistical significance was obtained, as reported in the Virginian-Pilot by Joanne Kimberlin. Recently, SharkDefense has developed a simple on-hook treatment and a bait attachment which are testing candidates on Atlantic longlining vessels during 3Q and 4Q2008.
. Teleost response was confirmed using captive Cobia
(Rachycentron canadum) and Pacific halibut
(Hippoglossus stenolepis). In July 2008, swordfish
(Xiphias gladius) catch was reported on experimental hooks treated with electropositive metal.
Shark repellent
A shark repellent is any method of driving sharks away from an area, object, person, or animal. Shark repellents are one category of animal repellents.-Overview:Shark repellents have been of interest to human beings for many years, for a number of reasons...
materials that produce a measurable voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
when immersed in an electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
such as seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
. The voltages produced are as high as 1.75 VDC in seawater. It is hypothesized that this voltage overwhelms the ampullary organ
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
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, so no external power input is required. As chemical work is done, the metal is lost 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.
History
SharkDefenseSharkdefense
SharkDefense is an internationally-recognized and award-winning research organization and think tank focused on shark bycatch reduction. Its core research involves chemical and electrochemical shark repellent technologies. SharkDefense's repellent experiments have been featured extensively in the...
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
Tonic immobility
Apparent death, colloquially known as playing dead or playing possum, is an antipredator behavior observed in a wide range of animals in which they take on the appearance of being dead to an observer...
experiment by Eric Stroud using a juvenile lemon shark
Lemon shark
The lemon shark, Negaprion brevirostris, is a shark in the family Carcharhinidae, that can grow to long. It is known as the lemon shark because, at certain depths, light interacting with the local seawater can give this shark a tanned and yellow pitted appearance, much like the surface of a...
(Negaprion 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 shark
Nurse shark
The nurse shark, Ginglymostoma cirratum, sometimes referred to as the Nur Shark is a shark in the nurse sharks family, the only member of its genus Ginglymostoma...
s (Ginglymostoma 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
Mike Rowe
Mike Rowe may refer to:*Michael Rowe, television writer for Futurama*Mike Rowe , host of the Discovery Channel show Dirty Jobs* Mike Rowe , retired Canadian professional ice hockey player...
, from Discovery Channel
Discovery Channel
Discovery Channel is an American satellite and cable specialty channel , founded by John Hendricks and distributed by Discovery Communications. It is a publicly traded company run by CEO David Zaslav...
’s Dirty Jobs
Dirty Jobs
Dirty Jobs is a program on the Discovery Channel, produced by Pilgrim Films & Television, in which host Mike Rowe is shown performing difficult, strange, disgusting, or messy occupational duties alongside the typical employees. The show premiered with two pilot episodes in November 2003...
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.
Further testing using salt bridge
Salt bridge
A salt bridge, in chemistry, is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell , a type of electrochemical cell...
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
Sharkdefense
SharkDefense is an internationally-recognized and award-winning research organization and think tank focused on shark bycatch reduction. Its core research involves chemical and electrochemical shark repellent technologies. SharkDefense's repellent experiments have been featured extensively in the...
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
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas in seawater via hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
, 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
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
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.
Testing
Stoner and Kaimmer (2008) reported success using cerium mischmetalMischmetal
Mischmetal is an alloy of rare earth elements in various naturally occurring proportions. It is also called cerium mischmetal, rare earth mischmetal or misch metal. A typical composition includes approximately 50% cerium and 25% lanthanum, with small amounts of neodymium and praseodymium...
and Pacific spiny dogfish
Spiny dogfish
The spiny dogfish, spurdog, mud shark, or piked dogfish, Squalus acanthias, is one of the best known of the dogfish which are members of the family Squalidae in the order Squaliformes. While these common names may apply to several species, Squalus acanthias is distinguished by having two spines ...
(Squalus acanthias, a type of shark) 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 Homer, Alaska
Homer, Alaska
Homer is a city located in Kenai Peninsula Borough in the U.S. state of Alaska. According to 2005 Census Bureau estimates, the population was 5,364. One of Homer's nicknames is "the cosmic hamlet by the sea"; another is "the end of the road"...
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 against Atlantic spiny dogfish in the Gulf of Maine
Gulf of Maine
The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...
. Mandelman et al. reported that the repellent effect disappeared after starvation using captive Atlantic spiny dogfish, and that a species-specific variation in response to the mischmetals exist between captive Atlantic spiny dogfish and dusky smoothhounds (Mustelis canis).
Stroud (SharkDefense, 2006) and Fisher (VIMS) observed captive cownose ray
Cownose ray
The cownose ray is a species of eagle ray found throughout a large part of the western Atlantic and Caribbean, from New England, USA to southern Brazil. Cownose rays grow rapidly, and male rays often reach about in width and weigh . Females typically reach in width and weigh .-Gestation:The...
s (Rhinoptera 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 shark
Sandbar shark
The sandbar shark, Carcharhinus plumbeus, is a species of requiem shark, family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by its very high first dorsal fin and inter-dorsal ridge....
s (Carcharhinus 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 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 sharkSandbar shark
The sandbar shark, Carcharhinus plumbeus, is a species of requiem shark, family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by its very high first dorsal fin and inter-dorsal ridge....
(C. plumbeus) catch when plastic decoys were compared to metals. A high statistical significance was obtained, as reported in the Virginian-Pilot by Joanne Kimberlin. Recently, SharkDefense has developed a simple on-hook treatment and a bait attachment 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 LorenziniAmpullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
. Teleost response was confirmed using captive Cobia
Cobia
Cobia —also known as black kingfish, black salmon, ling, lemonfish, crabeaters, aruan tasek, etc.—are perciform marine fish, the sole representative of their family, the Rachycentridae.-Description:...
(Rachycentron canadum) and Pacific halibut
Pacific halibut
The Pacific halibut is found on the continental shelf of the North Pacific Ocean and Bering sea. They are demersal, living on or near the bottom. The halibut is among the largest teleost fish in the world. Halibut are strong swimmers and are able to migrate long distances...
(Hippoglossus stenolepis). In July 2008, swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
(Xiphias gladius) catch was reported on experimental hooks treated with electropositive metal.