Using DTAGs to understand sound use, behavior, and vessel and associated noise effects in Southern Resident killer whales

• Main Authors: Holt, Marla M., Hanson, Brad, Emmons, Candice K., Giles, Deborah A., Hogan, Jeff, Tennessen, Jennifer
• Format: Text
• Language: English
• Published: Western CEDAR 2018
• Subjects: Killer whales; Vessel noise; Fresh Water Studies; Life Sciences; Marine Biology; Natural Resources and Conservation; Terrestrial and Aquatic Ecology; Killer Whale; Killer whale
• Online Access: https://cedar.wwu.edu/ssec/2018ssec/allsessions/466; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=2901&context=ssec

Prey availability and disturbance from vessels and noise are identified threats to the recovery of endangered Southern Resident killer whales. Vessels and noise can mask echolocation signals used to capture fish prey and/or disrupt foraging behavior with implications for energy acquisition. In the U.S., vessel regulations have been implemented since 2011 to protect killer whales from vessel disturbance, particularly given the extent of whale-watching activities in the Salish Sea. We utilized suction cup-attached digital acoustic recording tags (DTAGs), consisting of hydrophones and movement sensors, to measure received noise levels, understanding killer whale use of sound, and determine effects of vessels and noise on subsurface behavior. During the 29 tag deployments on individually identified killer whales, we collected detailed geo-referenced vessel data concurrently as conditions allowed, along with opportunistic observations of predation to validate feeding. Received noise levels (dB re 1microPa) were significantly different across years but not consistently lower after the implementation of vessel regulations. Of the vessel factors considered, both vessel count and speed, but not distance, explained differences in noise levels, which may reflect changes in whale-watching vessel practices after regulations implementation. Additionally, the analysis of data from these animal-borne tags allow us to better understand subsurface foraging behavior involving the use of sound, to quantify foraging rates at an individual level, and to understand detailed vessel and noise effects. The results, along with those of other related studies, inform conservation and management measures that aim to promote Southern Resident recovery.