Effect of interactive threats on foraging effort by endangered killer whales (Orcinus orca)

Abstract

Killer whales face many anthropogenic threats including vessel traffic, noise, and reduced prey availability. Here, we use high-resolution suction-cup Dtags to study the behavior of endangered Southern Resident killer whales that rely on biosonar to hunt salmon, and investigate how proximate vessels affect foraging behavior. From tag data, we identified subsurface behavior, including foraging and prey capture events. We then tested several vessel and associated sound, demographic, and environmental variables on behavioral state occurrence, time spent within each state, and foraging effort involving prey capture. Whales made fewer prey capture dives and spent less time in these dives when vessels had an average distance <400 yard (366 m). Lower prey abundance and higher vessel speed reduced prey capture probability, documenting the interplay between these effects. Finally, whales dove to depth more slowly while increasing dive duration to capture prey in the presence of vessel-emitted sonar, but descended more quickly with higher noise levels and closer vessels. Current efforts investigating foraging behavior and noise exposure over the diel cycle aim to better quantify foraging rates and activity budgets in this endangered population. These findings advance awareness of vessels and noise consequences on killer whales to inform conservation and management actions.