Effects of vessels and their sounds on the foraging behavior of endangered killer whales (Orcinus orca)

Abstract

Anthropogenic activities that have negative consequences on foraging outcomes warrant special concern in endangered species. Prey availability and vessel disturbance are identified risk factors of endangered Southern Resident killer whales (SRKW) as vessels and associated sounds can mask echolocation signals used for foraging and/or disrupt foraging behavior with implications for energy acquisition. To investigate vessel effects on foraging behavior, we utilized multi-sensor, digital acoustic recording tags (Dtags) that were suction cup-attached to SRKW. We tested a number of explanatory variables related to nearby vessels and associated sounds on the probability of prey capture and prey capture dive parameters. Tested variables included echosounder presence/absence, vessel counts, vessel distance, and vessel speed, and several competing received noise level measurements (absence of flow noise). Although noise level was not a significant explanatory variable on the probability of prey capture, flow noise limited available sample size. Furthermore, the probability of prey capture decreased as vessel speed increased which correlates with vessel noise. We also found a significant effect of echosounder presence on the duration and rate of descent of prey capture dives, indicating further consequences on foraging behavior. These results inform conservation and management efforts to preserve SRKW foraging opportunities and mitigate vessel disturbance.