Field experiments on electrically evoked feeding responses in the dogfish shark, Mustelus canis

Abstract

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.