Drs. Marla Holt, Brad Hanson, and Candice Emmons of the NWFSC, along with various collaborators, are currently conducting research 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 movement sensors used to derive pitch, roll, heading, jerk, 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).
Three main collaborative investigations rely on the data collected from DTAGs. The first study involves 117 daytime hours of DTAG data collected from Sep 2010 through Sep 2014, made possible through funding from the NOAA Ocean Acoustics Program. These data are used to: (1) document noise levels in biological relevant frequency ranges that are received by individual SRKWs and quantify the relationship between received noise levels and nearby vessels (Houghton et al. 2015); (2) compare noise levels before and after the implementation of vessel regulations to inform management of the effectiveness of the regulations (Holt et al. 2017); (3) investigate whale acoustic and fine scale movement behavior during different activities, including foraging, to understand sound use and behavior in specific biological and environmental contexts (Tennessen et al. 2019), and; (4) determine potential effects of vessels and associated noise on subsurface 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. Some analyses are completed while others are on-going, including work to address our third and fourth goals, which are partially funded by Sea World through the National Fish and Wildlife Foundation.
The second study aims to compare foraging behavior and vessel disturbance between two-transboundary populations of fish-eating killer whales. Both Northern and Southern Resident killer whales experienced population declines in the late 1990s and although NRKW numbers have since increased, the potentially prey-limited SRKW population has shown little recovery. Additionally, the impacts of vessel presence and noise are not equivalent between the core summer habitats of the two populations. Studies on SRKW have few data from quiet, low vessel-presence conditions and likewise, extremely high exposure events are less common, and thus harder to opportunistically sample for NRKW studies. This collaborative project will provide an opportunity to examine a greater range of disturbance conditions across populations. Specifically, we will analyze DTAG data collected by NWFSC and Department of Fisheries and Oceans Canada (DFO) scientists in both the United States and Canada to (1) describe and compare the subsurface foraging behavior of SRKW and NRKW, and (2) investigate how vessels/noise affect foraging behavior to reveal information critical to the effective management of both populations. This work is partially funded by the NOAA International Science Office and Department of Fisheries and Oceans Canada.
The third study will investigate patterns of foraging and behavioral activity states over a 24 hour (diel) cycle in Southern Resident killer whales, involving additional DTAG data collection beginning in the summer of 2018. Previous DTAG data collection efforts were limited to daytime hours given the need to collect detailed vessel data. This study will collect DTAG data during nighttime periods as well to understand whether the whales are doing something different after the sun sets. For example, do Southern Residents forage more during the day, in which the use of sound is critical? How do they use sound at night? Answers to these questions will address interactions of the prey availability and vessel/sound risk factors and help efforts to enhance foraging opportunities or mitigate disturbance from vessel traffic, which rely on a solid understanding of the biology and ecology of these whales. This work is largely funded by DFO.
The unique data obtained from DTAG field efforts 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 our research goals and to inform evidence based management actions.
Fact Sheet: Nighttime research on endangered killer whales may help protect them from noise (PDF).