Hotspots and behavioral patterns of southern Alaska resident killer whales (Orcinus orca)

Abstract

The resident killer whale (Orcinus orca) is a genetically and behaviorally distinct ecotype of killer whale that feeds primarily on Pacific salmon (Oncorhynchus spp.). Long-term monitoring over 30 years of study has enabled detailed investigation into pod-specific, seasonal, and compositional differences in space use and behavior. To investigate use of habitat, 33 resident killer whales representing 14 pods in the northern Gulf of Alaska were tagged with satellite transmitters during all years from 2006 to 2014, and transmissions were received during the months of June to January. Core use areas were identified through utilization distributions using a biased Brownian Bridge movement model. Tagging results indicate different core use areas between pods, which could be due to cultural transmission within matrilineal groups. To investigate differences in behavior, 1337 hours of behavioral data were collected from 2006 to 2015. For these observations, chi squared tests were used to determine significant differences in behavior budgets between seasons, regions, haplotypes, and numbers of pods. The presence of 'rarely sighted' pods (sighted in less than 5% of encounters) had a large influence on the frequency of social behavior, which increased from 18.5% without their presence to 31.4% with it (X² = 17.3, df = 1, P < 0.001). Frequency of social behavior was also significantly affected by the number of pods present (X² = 72.8, df = 3,P < 0.001), and increased from 4.7% to 31.2% with one pod to more than four pods present. Strong seasonal and pod-specific differences were found in core use areas, possibly driven by the availability of seasonal salmon migration. Social behavior, and to some extent foraging and resting behaviors, appear to be driven by group composition and numbers of pods throughout the spring to fall seasons. Overall, these findings help clarify spatial and behavioral patterns observed for resident killer whales.