Center for Marine Biodiversity and Conservation

The association between cetacean distributions and sea surface temperature fronts were examined within southern California’s California Cooperative Oceanic Fisheries Investigations (CalCOFI) study area. Quarterly surveys were performed from July 2004 through March 2008 to obtain cetacean distribution data. To examine the distribution and frequency of thermal front activity, monthly composite Advanced Very High Resolution Radiometer (AVHRR) satellite sea surface temperature (SST) imagery were acquired. Using Windows Image Manager (WIM) a Single Image Edge Detection (SIED) analysis was applied to each monthly image to identify locations of front activity. Front results were imported into ArcGIS 9.3 and cetacean sighting points overlaid. The distance to front activity and species richness in proximity to thermal front activity was analyzed. Results indicate a seasonal variation in front activity within the CalCOFI study area. The frequency of front activity peaks during the summertime (30%) while winter and spring activity dwindle to almost half the activity levels (13%). The spatial distribution of front activity also varies with season; during the spring front activity is contracted in shore and along the continental shelf near the Channel Islands. However, as the seasons progress front activity heightens offshore. Cetacean distributions were compared to a randomly generated point distribution using a 2-Sample Kolmogorov-Smirnov Test. In forty-five percent of the cruises, mysticetes returned a unique distribution curve, of which eighty-nine percent were in favor of front activity. Odontocetes returned non-random distribution curves in forty-three percent of the cruises, however, only twenty-two percent of these distributions were in favor of SST fronts. Cetacean richness and SST front activity were examined at a 10 km spatial scale; however, results showed little correlation between heightened front activity and increased species richness.