Effect of naval sonar exposure on killer whales and humpback whales – 3S-2023 cruise report

3S (Sea mammals and Sonar Safety) is a multidisciplinary and international collaboration studying how naval sonar affects cetaceans. The goal is to gain information necessary to manage the risk to cetaceans without unnecessarily restricting naval sonar activities. One of the objectives of phase 4 of the 3S project (3S4) is to investigate if exposure to Continuous Active Sonar (CAS) leads to different types or severity of behavioral responses than exposure to traditional Pulsed Active Sonar (PAS) signals. Another is to investigate empirically if responses from short duration experiments predict responses from longer duration exposures conducted over an operationally relevant duration. The 3S-2023 trial was conducted off the coast of Norway in October–November 2023 to collect data to address these research questions. The purpose of this report is to summarize and document the data collected.

The experimental design was based on short- and long-duration CAS and PAS exposures to killer whales and humpback whales using real-time GPS location data of multiple tagged subjects. The sonar source vessel was moved to achieve repeated dose escalations over 8 hours, and responses to the first approach will be compared to subsequent approaches in the analysis. Multiple whales were tagged with suction cup attached mixed-DTAG++, which records high resolution movement and acoustic data and transfers the GPS position of the tagged whales directly to the source vessel. Behavior was recorded for 8 hours before exposure, during the 8 hours long exposure and for 4–6 hours after exposure. In addition, Wildlife Computers SPLASH10-F-333B Limpet tags, which transfer lower resolution data via the Argos satellite, were deployed to record natural diurnal patterns of killer whales and potential responses to sonar of animals further away from the source. In addition to data on animal behavior recorded by the tags, we also collected data on the prey field in the area using echosounder and collected fish samples. Sound speed profiles were collected to understand how the sonar signals propagate in the area.

During the 3S-2023 trial, 13 mixed-DTAG++ and 6 satellite Splash tags were deployed to killer whales, and 5 mixed-DTAG++ were deployed to humpback whales. Of the 18 mixed-DTAG++ deployments, 11 were baseline-only records with durations varying from 5 minutes to 28.3 hours, and 2 were deployments on non-focal animals containing baseline and exposure data. Four long-duration controlled exposure experiments (two CAS and two PAS) on multiple focal animals (4 killer whales and 1 humpback whale) were conducted using direct GPS tracking. The Splash tags collected data on diurnal patterns of killer whales over periods from 1 to 7 weeks. Most tags were deployed to animals feeding around herring fishing vessels using purse seine.

The 3S-2023 trial was a success, although we were hoping to conduct more exposure experiments. However, such long duration exposure experiments have never been conducted before, and any data are highly valuable. We plan to collect more data during a similar trial in 2024. For the 3S-2024 trial, we recommend starting a week later to assure that the fishing fleet is in place when we start. We also have some concerns which need to be addressed about availability and reliability of DTAG core units and availability of a proper CAS source for 2024. A video showing the activities during the 3S-2023 trial can be seen following this link.