M.S. Marine Biology
Edward O. Keith
Daniel K. Odell
Pygmy sperm whales (Kogia breviceps) and dwarf sperm whales (Kogia sima) strand frequently in the southeastern United States (SEUS). To detect seasonal trends in Kogia sp. strandings across the SEUS, all 979 stranding events from 1977 through 2005 were segregated by month. A peak in strandings occurred in the late summer and early fall (July – October). The entire SEUS was divided into segments of similar coastline orientation, 1) North and South Carolina, 2) Georgia and the east coast of Florida, 3) Florida Keys, 4) west coast of Florida, 5) Florida panhandle, Alabama and Mississippi, 6) Louisiana and 6) Texas. Most areas displayed a significant peak in strandings in summer and a smaller significant peak in winter. A seasonal index analysis of the strandings revealed the same pattern as the general seasonal analysis. Analysis of wind direction changes preceding stranding events revealed six patterns. The most common pattern was when winds shifted from downwelling-favorable to upwelling-favorable during the week prior to a stranding. Analysis of sea level confirmed that when wind was upwelling-favorable, sea level decreased and when wind was downwelling-favorable, sea level increased.
Seasonal upwelling along central Florida’s Atlantic coast observed in the summer correlates with upwelling-favorable wind patterns during summer months, and increased Kogia sp. strandings. A smaller peak in strandings that occurs in the winter months appears to occur when there is a shift from the ‘normal’ downwelling-favorable conditions into a brief period of upwelling-favorable conditions. Along Florida’s Atlantic coast, distances to isobaths from stranding sites were not significantly different from distances of randomly selected sites to isobaths; however, there is a tendency towards shorter distances to isobaths. Along the Georgia, South Carolina and North Carolina coast, distances to isobaths from strandings sites are significantly different from distances of randomly selected sites to isobaths. The distinctive bathymetry of the SEUS Atlantic coast may contribute to strandings across the entire SEUS Atlantic coast. Analysis of the frequency of Kogia sp. strandings during the lunar cycle revealed no significant correlation between strandings and lunar day. Both wind direction and bathymetry may influence frontal structures and water movements, and thus abiotic environmental factors may be significant factors in determining the locations and timing of Kogia sp. stranding events.
Nicole M. O'Brien. 2008. An Analysis of Dwarf and Pygmy Sperm Whale (Kogia sp.) Stranding Data in the Southeast United States. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, Oceanographic Center. (244)