Southern Resident Killer Whale Digital Acoustic Recording Tag Research
Using digital acoustic recording tags (DTAGs) to examine sound exposure, sound use, and behavior of endangered Southern Resident killer whales.
We use digital acoustic recording tags (DTAGs) attached to the whales with suction cups to examine sound exposure, sound use, and behavior of Southern Resident killer whales in their core summer habitat.
Woods Hole Oceanographic Institution developed DTAGs specifically to monitor marine mammals' behavior and their response to sound throughout the dive cycle. Working under thoroughly reviewed research permits, we apply the tags to the whales with long poles. The tags include hydrophones that record sound and different movement sensors used to track pitch, roll, heading, jerk, and depth.
In previous tagging efforts during daytime hours, we typically saw the whales return to normal diving behavior within minutes after the tags were applied. The tags usually remain on the whales for several hours to about one day until they are programmed to release or fall off on their own.
The unique data obtained from DTAG field efforts shed light on Southern Residents' subsurface world, particularly on the importance of acoustics and specific movement patterns during foraging. These data improve our understanding of these endangered whales and inform evidence-based management actions.
DTAG data contributes to three collaborative investigations.
Vessel disturbance, noise exposure, and its impact on the Southern Residents
The first study involves 117 daytime hours of DTAG data collected from 2010-2014. We used these data to:
- Document noise levels in biological relevant frequency ranges received by individual animals and quantify the relationship between received noise levels and nearby vessels (Houghton et al. 2015).
- Compare noise levels before and after the implementation of vessel regulations to inform management of the effectiveness of the regulations (Holt et al. 2017).
- 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 (Holt et al. 2019, Tennessen et al. 2019a, Tennessen et al. 2019b).
- Determine the potential effects of vessels and associated noise on subsurface behavior (Holt et al. 2021a, Holt et al. 2021b).
This study improved our understanding of vessel disturbance, noise exposure, effects on foraging, and cumulative effects on this endangered population. Additionally, we have leveraged these valuable datasets for larger-scale comparative investigations such as Goldbogen et al. 2019.
Components of the work have been funded by the NOAA Ocean Acoustics Program and Sea World through the National Fish and Wildlife Foundation.
Foraging behavior and vessel disturbance in Northern and Southern Residents
In this study, we 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. Although Northern Resident numbers have since increased, the Southern Resident population has not. Additionally, the impacts of vessel presence and noise are not equivalent between the two populations' core summer habitats.
Studies on Southern Residents have few data from quiet, low vessel-presence conditions. Likewise, extremely high exposure events are less common and harder to sample opportunistically during Northern Resident encounters.
This collaborative project will provide an opportunity to examine a greater range of disturbance conditions across populations. We will analyze DTAG data collected by Center scientists and those from the Department of Fisheries and Oceans Canada to:
- Describe and compare the subsurface foraging behavior of Southern and Northern Residents (Tennessen et al. 2023).
- Investigate how vessels and noise affect foraging behavior to reveal information critical to both populations' effective management.
The NOAA International Science Office and Department of Fisheries and Oceans Canada partially funded this work.
Nighttime research on Southern Residents
We are investigating patterns of foraging and behavioral activity states over a 24 hour (diel) cycle in Southern Resident killer whales, involving new DTAG data collection beginning in 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 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 sound is critical? How do they use sound at night?
Answers to these questions will address the prey availability and vessel and sound risk factors' interactions. Further, they will aid efforts to enhance foraging opportunities or mitigate disturbance from vessel traffic, which relies on a solid understanding of the biology and ecology of these whales.
The Department of Fisheries and Oceans Canada funds much of this work.