MAGNETIC FENCING
The following video samples demonstrate how swim patterns in juvenile lemon sharks are altered using a half-submerged permanent magnetic perimeter comprised of Barium-Ferrite magnetic blocks.
Juvenile lemon shark swim behavior without a magnetic perimeter. Notice that the sharks utilize most of the internal pen area.
Juvenile lemon shark swim behavior using a full pen diameter magnetic perimeter (half-buried black line at center). Notice the tight circular swim patterns to the right of the barrier.
TONIC IMMOBILITY
"Rare" earth magnets have been demonstrated to terminate tonic immobility (i.e. a comatose state in sharks induced by turning them upside-down; TI) in several shark species including lemon sharks (Negaprion brevirostris) and nurse sharks (Ginglymostoma cirratum). Once the comatose or "tonic" state in sharks is achieved, it is difficult to interrupt. Therefore, it is a technique often employed during surgical procedures on sharks (e.g. internal tag implantation). Our primary assumption for using TI bioassays to test repellent effects is that a treatment that interrupts TI suggests that it may be a good repellent.
Immobilized lemon shark with blinder rousing when a 4" NdFeB magnet is presented. (The original experiment from February 2005 !!) The shark bends away from the magnet.
Immobilized lemon shark with blinder rousing when a 1" NdFeB cylinder magnet is presented. The shark bends away from the magnet.
MYSTERY METALS
The following video samples (left column) demonstrate the behavioral effects of highly electropositive metals and alloys on immobilized sharks. The violent rousing reaction appears to be produced within the range of the Ampullae of Lorenzini's detection distance. Behavioral controls are given in the right column for comparison.
REPELLENT EXPERIMENTS
Immobilized lemon shark without blinder using Praseodymium metal - VIOLENT !
Immobilized lemon shark without blinder using Samarium metal.
Immobilized lemon shark without blinder using Neodymium metal - VIOLENT !
Immobilized lemon shark without blinder using Ytterbium metal - VIOLENT !
Immobilized lemon shark without blinder using Holmium metal (weaker response due to increased electronegativity).
Immobilized nurse shark with blinder using Cerium Mischmetal.
CONTROL EXPERIMENTS
Immobilized lemon shark without blinder / Samarium metal is moved in air and does not contact water.
Immobilized nurse shark without blinder / Motion of hand does not terminate tonic state.
Immobilized lemon shark without blinder / Pyrolytic graphite (diamagnetic) does not terminate tonic state.
Immobilized lemon shark without blinder / Tungsten metal does not terminate tonic state.
Immobilized lemon shark without blinder / Zirconium metal does not terminate tonic state.
Immobilized lemon shark without blinder / Cobalt metal (ferromagnetic) does not terminate tonic state.
MAGNETIC MAZES
An acrylic Y-maze was constructed to establish a preference test for several species of captive sharks. Sharks were allowed to enter and exit the maze without negative reinforcement if the correct path was chosen. For each trial, raw shrimp was used as the reward, and a 4"x1.5" cylindrical "rare" earth magnet (grade = N48) was used as negative reinforcement. In a series of trials reported at the July 2005 American Elasmobranch Society (AES) meeting in Tampa, Florida, SharkDefense reports that juvenile nurse sharks entering the trap of the maze (i.e. branch with the magnet) became very distressed and would not take any reward baits. Two nurse sharks clearly learned to avoid the magnet trap and take the reward baits during a period of 6 trials. Results were similar when the trap was placed in the other branch of the Y maze. During one of the replicate trials, a third nurse shark entered the trap and became highly distressed and needed to be rescued from the maze. This shark never entered the maze again in subsequent trials. A juvenile lemon shark became highly distressed when approaching the junction towards the magnet, and did not take any rewards.
A juvenile nurse shark chooses the magnetic "trap" of the Y-maze.
The magnetic field is sensed and the shark begins to forcefully back up.
The shark is able to move back to the junction.
The shark chooses another leg, exiting the maze.
In a separate experiment, a nurse shark chose the magnetic trap and could not back up.
The shark becomes highly distressed and had to be rescued.
Magnetic mazes can also be constructed using Barium-Ferrite blocks in large open-water pens. Below are preliminary studies using two types of maze designs.
A nurse shark displaying a 180 degree turn when encountering the maze for the first time.
Two nurse sharks learning to navigate a magnetic perimeter "maze", illustrated at left. The maze is constructed of half-buried barium-ferrite blocks.
Interesting behavior seen with juvenile lemon sharks and a half-pen magnetic perimeter. While some sharks do cross over the perimeter, a number of sharks were observed following the magnetic field "wall" or turning abruptly away from the perimeter. The right side of the screen has no magnetic perimeter.