Blue whale (Balaenoptera musculus) behavior and group dynamics as observed from an aircraft off southern California 2008-2013

About

Group behavior and interactions of endangered blue whales (Balaenoptera musculus) have not been systematically studied. We hypothesized that response variables of blue whale sighting rate, group type and cohesion differed by the explanatory variables behavior state, time of day, season, water depth and distance from shore. To address our hypotheses, we flew systematic line transect surveys in southern California and collected focal group data. Chi-square contingency table and G² analyses were used to assess statistical relationships between response and explanatory variables. Observation effort totaled 87,555 km involving 18 (1-week-long) aerial surveys spanning Jan-Dec 2008-2013. Seventy blue whale groups (117 individuals) were seen, ranging in size from 1-6 whales (mean = 1.7, SD = 1.20). Results supported our hypotheses that blue whale group characteristics were influenced by behavior state and spatiotemporal variables. Sighting rates were significantly highest during summer followed by spring, fall and winter (p