| Summary: | On Mesoscale Population Study cruises during summers 2004 and 2005 aboard the sailboat Summer Breeze, researchers from the Sperm Whale Seismic Study (SWSS) surveyed for sperm whales along the continental slope of the northern Gulf of Mexico. SWSS scientists tracked 35 groups of whales during these two summers, recording locations where they did and did not encounter whales. Whales were encountered during both summers at approximately the same frequency (19 groups in 38 survey days in 2004; 16 groups in 29 survey days in 2005), but fluke photo-identifications indicated that 85% of individuals encountered during summer 2005 had never been previously identified in the Gulf throughout 10 years of cetacean research. Composition and distribution of these groups also varied between summers. Oceanographic conditions at the edge of the continental shelf differed between 2004 and 2005, which may have modified the usual trophic cascade that begins with near-surface primary production to create local aggregations of prey at the depths where sperm whales forage. Sperm whales are apex, mesopelagic predators, but have been shown to associate with surface primary productivity over large spatial scales and time scales of months to years. The purpose of this thesis was to look for relationships between sperm whale presence and surface oceanography on smaller spatial and shorter temporal scales. Surface ocean color from NASA?s Moderate Imaging Spectroradiometer (MODIS) and surface dynamic height from NASA?s Earth orbital altimeters were evaluated to assess habitat occupied by sperm whales. Passive acoustic monitoring along transect lines for sperm whale clicks permitted determination of sperm whale presence and absence. Sperm whale encounters were in general associated with negative sea surface height and enhanced sea surface chlorophyll (SSC), especially in or near areas where local SSC anomaly was produced by cyclone induced upwelling of nutrients or from coastal water advected off-margin. During summer 2004, SSC was generally high all along the upper continental slope whereas summer 2005 saw relatively low SSC along the upper continental slope. Whales encountered in this study were most highly correlated with SSC two weeks after the initial development of locally highest-SSC anomalies.
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