title: Fine-scale foraging movements by fish-eating killer whales (Orcinus orca) relate to the vertical distributions and escape responses of salmonid prey (Oncorhynchusspp.).
abstract: BACKGROUND
  We sought to quantitatively describe the fine-scale foraging behavior of northern resident killer whales (Orcinus orca), a population of fish-eating killer whales that feeds almost exclusively on Pacific salmon (Oncorhynchusspp.). To reconstruct the underwater movements of these specialist predators, we deployed 34 biologging Dtags on 32 individuals and collected high-resolution, three-dimensional accelerometry and acoustic data. We used the resulting dive paths to compare killer whale foraging behavior to the distributions of different salmonid prey species. Understanding the foraging movements of these threatened predators is important from a conservation standpoint, since prey availability has been identified as a limiting factor in their population dynamics and recovery.
  
  
  RESULTS
  Three-dimensional dive tracks indicated that foraging (N= 701) and non-foraging dives (N= 10,618) were kinematically distinct (Wilks' lambda:λ16= 0.321,P< 0.001). While foraging, killer whales dove deeper, remained submerged longer, swam faster, increased their dive path tortuosity, and rolled their bodies to a greater extent than during other activities. Maximum foraging dive depths reflected the deeper vertical distribution of Chinook (compared to other salmonids) and the tendency of Pacific salmon to evade predators by diving steeply. Kinematic characteristics of prey pursuit by resident killer whales also revealed several other escape strategies employed by salmon attempting to avoid predation, including increased swimming speeds and evasive maneuvering.
  
  
  CONCLUSIONS
  High-resolution dive tracks reconstructed using data collected by multi-sensor accelerometer tags found that movements by resident killer whales relate significantly to the vertical distributions and escape responses of their primary prey, Pacific salmon.
authors.affiliation: Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, AERL Building, Room 247 - 2202 Main Mall, Vancouver, BC V6T 1Z4 Canada.|Department of Zoology, University of British Columbia, #4200 - 6270 University Blvd., Vancouver, BC V6T 1Z4 Canada.|Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo, BC V9T 1K6 Canada.
authors.forename: Brianna M
authors.initials: BM
authors.lastname: Wright
authors.affiliation: Department of Zoology, University of British Columbia, #4200 - 6270 University Blvd., Vancouver, BC V6T 1Z4 Canada.|Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo, BC V9T 1K6 Canada.
authors.forename: John K B
authors.initials: JKB
authors.lastname: Ford
authors.affiliation: Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo, BC V9T 1K6 Canada.
authors.forename: Graeme M
authors.initials: GM
authors.lastname: Ellis
authors.affiliation: Centre for Wildlife Conservation, University of Cumbria, Rydal Road, Ambleside, Cumbria L22 9BB UK.
authors.forename: Volker B
authors.initials: VB
authors.lastname: Deecke
authors.affiliation: Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543-1050 USA.
authors.forename: Ari Daniel
authors.initials: AD
authors.lastname: Shapiro
authors.affiliation: Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, AERL Building, Room 247 - 2202 Main Mall, Vancouver, BC V6T 1Z4 Canada.|Department of Zoology, University of British Columbia, #4200 - 6270 University Blvd., Vancouver, BC V6T 1Z4 Canada.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Battaile
authors.affiliation: Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, AERL Building, Room 247 - 2202 Main Mall, Vancouver, BC V6T 1Z4 Canada.|Department of Zoology, University of British Columbia, #4200 - 6270 University Blvd., Vancouver, BC V6T 1Z4 Canada.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Trites
keywords: Accelerometry; Biologging; Diving behavior; Dtag; Foraging; Killer whale; Movement; Orcinus orca; Pacific salmon