Dear colleagues, My co-authors and I are please to announce the publication of our new paper titled: Foraging Behaviour and Ecology of Transient Killer Whales Within a Deep Submarine Canyon System. McInnes, J.D., Lester, K.L., Dill, L.M., Mathieson, C.R., West-Stap, P.J., Marcos, S.L., and Trites, A.W. (2024). Foraging Behaviour and Ecology of Transient Killer Whales Within a Deep Submarine Canyon System. PLoS ONE 19(3): e0299291. https://doi.org/10.1371/journal.pone.0299291. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0299291 Summary: Transient killer whales have been documented hunting marine mammals across a variety of habitats. However, relatively little has been reported about their predatory behaviours near deep submarine canyons and oceanic environments. We used a long-term database of sightings and encounters with these predators in and around the Monterey Submarine Canyon, California to describe foraging behaviour, diet, seasonal occurrence, and habitat use patterns. Transient killer whales belonging to the outer coast subpopulation were observed within the study area 261 times from 2006–2021. Occurrences, behaviours, and group sizes all varied seasonally, with more encounters occurring in the spring as grey whales migrated northward from their breeding and calving lagoons in Mexico (March-May). Groups of killer whales foraged exclusively in open water, with individuals within the groups following the contours of the submarine canyon as they searched for prey. Focal follows revealed that killer whales spent 51% of their time searching for prey (26% of their time along the shelfbreak and upper slope of the canyon, and 25% in open water). The remainder of their time was spent pursuing prey (10%), feeding (23%), travelling (9%), socializing (6%), and resting (1%). Prey species during 87 observed predation events included California sea lions, grey whale calves, northern elephant seals, minke whales, common dolphins, Pacific white-sided dolphins, Dall’s porpoise, harbour porpoise, harbour seals, and sea birds. The calculated kill rates (based on 270 hours of observing 50 predation events) were 0.26 California sea lions per killer whale over 24 hours, 0.11 grey whale calves, and 0.15 for all remaining prey species combined. These behavioural observations provide insights into predator-prey interactions among apex predators over submarine canyons and deep pelagic environments. Please feel free to email me with any questions: j.mcinnes@oceans.ubc.ca Sincerely, Josh D. McInnes, MSc Candidate Marine Mammal Research Unit Institute for the Oceans and Fisheries Aquatic Ecosystem Research Laboratory University of British Columbia Vancouver, BC Canada V6T 1Z4 Research Associate | Pacific Wildlife Foundation Port Moody, British Columbia, Canada, V3H 1V6 Centre for Wildlife Ecology Department of Biological Sciences 8888 University Drive Simon Fraser University, Burnaby, BC