Earthquake-Sensing Fish

Do fish have the ability to sense the occurrence of very small earthquakes, earthquakes that might be forewarning of bigger events to come? It seems that they might, according to an article in the August 1980 issue of Geophysical Research Letters written by University of Texas researchers, Cliff Frohlich and Ruth Buskirk.

Experiments with codfish, goldfish and other fish have shown that fish are able to sense very small changes in pressure and motion within the water where they live. That is, they are able to hear very weak sounds. As in air, a sound heard in water is the result of compressional waves traveling through the medium, except that sound waves travel about five times faster in water than they do in air.

In addition to sound detection in the inner ear, a fish is able to sense sound stimuli with extensive arrays of hair cell receptors along its body and also with sensors that detect changes within the swim bladder. These multiple sensing abilities combine to allow the fish to detect tiny sounds, some of which are far lower in frequency than a human can detect.

People do sometimes hear sound waves in air associated with passing seismic waves in the ground below. Sound waves generated in water by earthquake waves in the rock below are much stronger than those generated in air. That and the fish's ability to sense weak sound waves combine to permit a fish to "hear" earthquakes that are ten to a thousand times smaller than a person can hear.

Researchers Frohlich and Buskirk suggest that fish may detect nearby earthquakes resulting from tiny breakage of rocks along small faults, faults with lengths as short as a meter-stick, perhaps even shorter.