Characterizing the habitat and diving behavior of satellite-tagged blue whales (Balaenoptera musculus) off California

Graduation date: 2008This study was designed to identify and characterize areas of concentrated use and diving behavior of blue whales (Balaenoptera musculus) off the California coast. During the summer of 2004, thirteen blue whales were tagged with implantable Telonics ST-15 Argos satellite-monitored radio tags and five were tagged with Telonics ST-21 Argos satellite-monitored depth of dive tags. Tag duration averaged 100 d with a total of 2159 locations recorded. Whales generally remained near the continental slope and were most often found at the west end of the Santa Barbara Channel, near the Gulf of the Farallones, or between Cape Mendocino and Cape Blanco. Analysis of the 95% kernel density distributions of whale locations showed a one degree increase in sea surface temperature (SST) was correlated with a decrease in whale density by 7% (p < 0.0001) while density was highest at a surface chlorophyll level of 4.5 mg/l and a water depth of 1573 m (p < 0.001 each). These results show that tagged whales were most likely to be found in areas of strong upwelling along the slope edge. Dive data from 414 summary periods showed whales spent at least 50% of their time in the top 50 m of the water column and up to 94% of their time there at night. Daytime average dive depth was 2.3 times deeper than during the night, probably due to the vertical migration of some euphausiid species upon which blue whales feed. Differences in mean number of dives and mean maximum dive duration suggest a behavior change during the night, possibly a period of rest. Whales dove less frequently as swim speed increased, and more frequently as water depth increased. No significant variation in daytime average dive depth was observed between clustered and linear location types, however fewer total dives were made during linear location types suggesting whales were making exploratory dives to foraging depths while traveling