THE ROLE OF SNAPPING SHRIMP (CRANGON AND SYNALPHEUS) IN THE PRODUCTION OF UNDERWATER NOISE IN THE SEA

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Abstract
The most widespread of all biological noises known to exist in the sea is an intense high frequency crackle which was found to be caused by snapping shrimp (Crangon and Synalpheus). The noise produced by an individual shrimp is an occasional single sharp "snap," but the activity of a large population results in a continuous crackle with a diurnal variation of only about 2 to 5 db. No seasonal variation has been observed in the latitude studied. Sound analyses of this noise reveal that the strongest components are in the frequency range 2 to 15 kc. Above 10 kc it is some 30 db above water noise of state 1 sea. Fourier integral analysis of single shrimp snaps shows components similar to those observed over shrimp beds. The areas of crackling noise are correlated directly with habitats favorable to snapping shrimp, i.e., bottoms covered with rock, coral, shell, etc., in depths of 30 or less fathoms of water. The distribution of underwater crackle is shown to agree with the geographical range of these genera of shrimp. They are tropical and subtropical; the northern and southern boundaries falling roughly at the 11[degree]C surface isotherm, hence between about 35[degree]N and 40[degree]S.

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