(Woods Hole Oceanographic Institution, 1981-05)
Dawson, Benjamin G.; Heyer, Gail W.; Eppi, Rene E.; Kalmijn, Adrianus J.
From previous experiments, we learned that sharks, skates and rays have
an electric sense that enables them to detect voltage gradients as low as
0.01 µV/cm within the frequency range from DC up to 8 Hz. The animals use
their electric sense in predation, cuing in on the bioelectric fields commonly
produced by fish and aquatic invertebrates. To quantify the response, we
analyzed the feeding behavior of the shark Mustelus canis in Vineyard Sound
off Cape Cod, Mass. An electrode panel was embedded in the ocean substrate
in a water depth of 2-3m. Two salt-bridge electrodes, simulating a small
prey fish, were placed 2 em apart at a distance of 15 cm from a centrally located
odor source. Another pair of salt-bridge electrodes, simulating a
larger fish, were placed 5 em apart at a distance of 30 cm on the other side
of the odor source. DC current of 8 µA was applied to either one or both
pairs of electrodes. Observations were made at night from a Boston Whaler
with a glass bottomed observation well. Liquefied herring chum attracted
and motivated sharks.
In sum, the results support the conclusion that these sharks, once motivated
by odor rely heavily upon their keen electric sense in executing their
final strikes.
