Sperm whale research in the Gulf of Mexico.

Abstract

Sperm whales occur throughout the oceanic Gulf of Mexico. Most research has been conducted in the northern Gulf where, until 2000, studies focused on abundance and distribution. Based on ship surveys conducted from 1996 to 2001, sperm whale density in the northern Gulf is 0.35 whalesC100km-2 with an abundance of 1,349 whales (CV = 0.23) This estimate is negatively biased because it is not corrected for subsurface whales (i.e. g(0) < 1). Sperm whales occur throughout northern Gulf waters but there are concentrations near the Mississippi River delta and in the southeastern Gulf. Seasonal aerial surveys of slope waters in the northern Gulf indicated sperm whales are present throughout the year. In 2000, research was initiated that included habitat studies, genetics, satellite tagging, shortterm acoustic tagging, acoustic monitoring, photo-identification, and prey studies. Through 2002, all aspects of this research have been extremely successful, however, in most cases only preliminary results are available. One satellite tagged whale traveled from the northern Gulf to the southern Gulf. Photo-identification studies indicate that some sperm whales either display site fidelity to small regions of the Gulf or return to those regions on a routine basis. Preliminary analyses of samples from free-ranging animals (floating fecal material) and stomach contents of stranded animals indicate that Gulf sperm whales feed on meso- and bathypelagic species of cephalopods. Genetic information from 89 individual sperm whales indicate that the majority of whales found in groups in the north-central Gulf fit the 'mixed' group scenario. However, some bachelor groups may also reside in the Gulf. Mitochondrial DNA (mtDNA) analyses showed that groups are comprised of both single and mixed matrilines. Two mtDNA haplotypes from the northern Gulf of Mexico appear to be unique on a global scale to this area. Significant differentiation between geographic areas was revealed for the maternally inherited mtDNA, but not for the bi-parentally inherited nuclear genome analysis.