| Summary: | The Salish Sea is home to two at-risk populations of fish-eating killer whales with divergent population trajectories. Over the past two decades, the threatened Northern Resident population (NRKW) has been growing steadily while the endangered Southern Resident population has exhibited no net growth. One of the primary risk factors threatening recovery of these populations is the availability and accessibility of preferred salmonid prey, yet the factors that interfere with killer whale foraging success are poorly understood due to the challenges of quantifying foraging behavior that typically occurs out of sight. We addressed this challenge by leveraging fine-scale behavioral data from high-resolution sound and movement biologging tags suction cup-attached to 52 individuals from the NRKW and SRKW populations during August and September in 2009-2014. Specifically, we explored the relationships between predictors including sex, population, demography and noise level, and several foraging-related response variables including prey capture rates and efficiency, number of prey captured, and likelihood of occurrence of sounds and movements associated with foraging behavior and success. We found that prey capture and foraging efficiency rates were affected by an interaction between population and sex: whereas female SRKW exhibited less foraging activity than their male counterparts, the converse was true for NRKW. Additionally, number of prey captured was predicted by a negative effect of calf presence in adult females, and an interaction between population and whether a mother was alive in adult males. Finally, we found significant effects of ambient noise level, measured between 15-45 kHz within a dive, on the likelihood of clicking (searching), buzzing (chasing prey), prey capture, and dive duration. We discuss these results in the context of differing levels of human disturbance, unbalanced demographic structure and different growth trajectories on recovery of these at-risk populations of killer whales in the Salish ...
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