High-resolution archival tags provide new insights into the underwater foraging and echolocation behavior of resident killer whales capturing Pacific salmon

• Main Author: Wright, Brianna
• Format: Text
• Language: English
• Published: Western CEDAR 2018
• Subjects: Killer whale; Dtag; Biologging; Foraging; Behaviour; Chinook salmon; Fresh Water Studies; Life Sciences; Marine Biology; Natural Resources and Conservation; Terrestrial and Aquatic Ecology; Pacific; Killer Whale
• Online Access: https://cedar.wwu.edu/ssec/2018ssec/allsessions/454; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=2889&context=ssec

Dtags contain sensors for recording both high resolution animal movement and underwater sound. They provide a valuable tool for examining the foraging behavior of resident killer whales, a specialist predator that relies on echolocation to find and pursue Pacific salmon, its primary prey. We deployed Dtags on 32 northern residents off Vancouver Island, BC, and compared reconstructed whale dive paths to distributions of different salmonid prey. Foraging whales dove deeper, remained submerged longer, swam faster, increased their dive path tortuosity, and rolled their bodies more than during other activities. Foraging dive structure also reflected the deeper vertical distribution of Chinook salmon and revealed several predator evasion strategies used by salmonids. Echolocation by resident killer whales during 17 successful salmon captures was also examined in detail. For each capture, whales produced an average of 14.3 regular click trains with mean repetition rates of 10 clicks s-1, and 2.5 ‘buzzes’ with rapid click rates exceeding 50 clicks s-1. Most buzzes occurred at depths >100 m and preceded prey captures, which is consistent with their presumed function of close-range prey targeting. Once salmon were caught, both the mean proportion of time that whales spent echolocating and the mean clicking rate decreased significantly, confirming that echolocation plays an important role in prey detection and tracking. Distinctive ‘crunches’ were audible at shallow depths (m) following captures, indicating that killer whales brought most fish to the surface for handling and consumption. DFO and NOAA are now conducting a transboundary study using Dtag data to compare the foraging behavior of endangered southern residents with that of the growing northern resident population. Investigating differences in foraging efficiency between these two populations, including the impact of vessel noise exposure, will help to clarify factors impeding the recovery of southern residents, and identify strategies to best mitigate these ...