Drs. Marla Holt, Brad Hanson, and Candice Emmons of the NWFSC, along with collaborators from Cascadia Research Collective, University of Washington, and UC Davis, are currently conducting a study using digital acoustic recording tags (DTAGs) to examine sound exposure, sound use and behavior of Southern Resident killer whales (SRKWs) in core summer habitat. The DTAG is temporally attached with suction cups and consists of hydrophones that record sound and a number of different sensors used to derive pitch, roll, heading, and depth. The tag was developed by Woods Hole Oceanographic Institution specifically to monitor the behavior of marine mammals, and their response to sound, continuously throughout the dive cycle. Prey samples and vessel data are also concurrently collected relative to tagged whales in a manner similar to previous work (Giles and Cendak 2010, Hanson et al. 2010).
The project research goals include: (1) measure noise levels in biological relevant frequency ranges that are received by individual SRKWs; (2) quantify the relationship between received noise levels and detailed vessel traffic variables obtained from precise geo-referenced data collected concurrently; (3) investigating whale acoustic and fine scale movement behavior during different activities, including foraging, to understand sound use and behavior in specific biological and environmental contexts; and; (4) determining potential effects of vessels and associated noise on behavior. The results of this study will provide pertinent data to address multiple risk factors of SRKWs including vessel disturbance, noise exposure, effects on foraging, and cumulative effects.
Data collection for the DTAG project wrapped up in late-September 2014, yielding a total of 117 hours of DTAG data from 29 tag deployments since the project began in 2010. Results thus far demonstrate that noise levels recorded from the whales are variable with specific vessel attributes predictive of the measured noise levels (Houghton et al. 2015 ). Other analyses are on-going including work to address our third and fourth goals, which are partially funded by the National Fish and Wildlife Foundation (NFWF) Killer Whale Research and Conservation Program.
The unique data obtained from this project using DTAGs shed light on the subsurface world of SRKWs, particularly on the importance of acoustics and specific movement patterns during foraging in SRKWs. Examples are illustrated to the right (see Multimedia box) and include the acoustic behavior, the pitch, roll, and three-dimensional tracks of two whales during foraging dives. Example vessel data are also shown during one of the tag deployments. Such data are critical for addressing the study's research goals.