Spatial and temporal variation of sperm whale (Physeter macrocephalus) codas in the northern Gulf of Mexico

Abstract

Sperm whale (Physeter macrocephalus) codas, short rhythmic patterns of clicks, were recorded annually from a towed linear array throughout the northern Gulf of Mexico during 2-week cruises spanning October 1991–August 1997. Codas were sampled and classified according to their temporal pattern and the number of clicks they contained. Regular codas, with equally spaced intervals between clicks, were analyzed along with irregular codas, with double intervals between the last two clicks. In this sample, short codas (less than five clicks) were more common than long codas (greater than six clicks). Preliminary analysis (n=11), using Student’s t-test, suggests that irregular codas may not vary in the northern Gulf of Mexico. When comparing interclick intervals, irregular coda types did not differ significantly across multiple years, and no spatial variation was observed. This pattern of similarity in coda types, if upheld with additional analyses, may suggest that coda repertoires remain stable over periods of years or that a resident population of animals may inhabit this area. Further analysis, however, is required to substantiate this supposition. [Work supported by Texas A&M University at Galveston.]