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.
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).
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 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.
[3] Stoner and Kaimmer (2008)[4] reported success using cerium mischmetal and Pacific spiny dogfish (Squalus acanthias, a type of shark) in captivity, both with tonic immobility and feeding preference tests.
[6] Stroud (SharkDefense, 2006) and Fisher (VIMS) observed captive cownose rays (Rhinoptera bonasus) changing swim elevation and ignoring blue crab baits in cages that contained neodymium-praseodymium mischmetal.
Brill et al. (2008) reported that captive juvenile sandbar sharks (Carcharhinus plumbeus) maintained a 50–60 cm 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.
In July 2008 Richard Brill of NMFS/VIMS and SharkDefense both conducted more at-sea trials with electropositive metals in an effort to reduce shark bycatch in commercial fisheries.
Favaro and Cole (2013) determined through meta-analysis that electropositive metals did not reduce elasmobranch by-catch in commercial long-line fisheries,[7] which raises concerns on the effectiveness of this approach as a shark deterrent or repellent to protect water users.