Meeting Abstract

33.6  Monday, Jan. 5  Lanthanide Metals as Shark Repellants KAJIURA, Stephen M; Florida Atlantic University kajiura@fau.edu

Sharks possess an exquisitely sensitive electrosensory system that enables them to detect voltage gradients in their environment. At close range, this sensory modality overrides other senses and provides the sharks with spatial information to localize their prey. The electric field surrounding prey items is approximated by a dipole and sharks vigorously bite at prey-simulating dipole electric fields in the environment. Whereas higher order electric fields are also present, monopoles are absent in nature. However, the electropositive nature of lanthanide metals may provide a monopole source with a sufficiently strong local electric field to disrupt the sharks electrosense. This was tested by quantifying the electric field characteristics of various lanthanide metals and alloys (Nd, Nd-Pr, Cs-La) at the range of temperatures (10, 20, 30C) and salinities (0, 15, 35ppt) naturally encountered by sharks. All metals produce a measurable electric field in the seawater, in the range of millivolts, with the alloys generating a greater voltage than the Nd. The voltage of all metals declines with distance with a power function of y=x^-1.3. Although the measured voltage did not demonstrate a strong correlation with temperature, it did exhibit a strong inverse relationship with salinity. Behavioral assays demonstrated that various elasmobranch species were repelled from a food source when any of the metals were present, but readily ate in the absence of a metal. Teleost fishes were unaffected by the metals. The strong adversive reaction of the sharks to the metals suggests a possible utility of the metals as a bite deterrent which could reduce shark by-catch on long line fishing gear.