Studying the effect of source proximity in sperm whales and continous sonar in pilot whales using operational sonars - the 3S-2019-OPS cruise report

The 3S project is an international collaborative effort with the aim to investigate behavioral reactions of cetaceans to naval sonar signals. The objectives of the third phase of the project are 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, and to investigate how the proximity of the source to a whale affects behavioral responses. This report summarizes the efforts, activities and data collection of the 3S-2019-OPS research trial conducted over 4 weeks in Norwegian waters in August-September 2019. The primary tasks of the trial were to tag sperm whales with mixed-DTAGs and expose them to PAS at different levels and ranges, and to tag long-finned pilot whales with Mixed-DTAG and expose them to PAS and CAS. When a target species was localized, a tag boat was launched and mixed-DTAGs deployed. The mixed-DTAG contained a GPS, an Argos satellite transmitter, triaxial accelerometers and magnetometer sensors, stereo acoustic sensors and a pressure sensor. In addition to the tags, data on potential vocal responses or avoidance of the exposed area were collected by two moored acoustic buoys. Tagged whales were subject to controlled sonar exposure experiments (CEE). The experimental design involved dose escalation at different ranges and maximum source levels using operational sources towed by the FFI research vessel HU Sverdrup II (HUS) or the Norwegian Navy frigate KNM Otto Sverdrup (OSVE). The experiments were conducted under permit from the Norwegian Animal Research Authority, and all procedures were approved by the Animal Welfare Ethics Committee at the University of St Andrews. A separate risk assessment and management plan was developed for the trial to minimize risk to the environment and third parties. During trial we deployed 24 tags onto 20 different animals (15 sperm whales and 5 pilot whales), and collected 355 hours of tag data. We conducted 11 experiments, including 10 controlled exposure experiments with 25 exposure runs to sperm whales. Using the CAPTAS source on OSVE we conducted 7 CEEs with 16 exposure runs, and using the SOCRATES source on HUS we conducted 3 CEEs with 9 exposure runs. During 1 session with pilot whales we only collected baseline data, because the tags detached prematurely before any exposures. What we achieved during the trial was the collection of a unique dataset, and the trial is considered to be successful. We expect that the data collected on sperm whales will be sufficient to answer the questions related to the effect of source proximity on responses. Unfortunately, the question of the effect of CAS on pilot whales cannot be answered with the data collected. Additional field effort is required to achieve this. This primary task was given significant priority, with 7-10 out of 24 days of ship time dedicated to it, and 20 hours of baseline data collected on pilot whales. Despite this effort, the outcome was marginal. Weather conditions were rough early in the trial when this task had highest priority, and no pilot/killer whales were found in the protected fjords. When the weather was acceptable we found pilot whales only once. Unfortunately, the behavior of the tagged pilot whales led to early tag release in worsening weather, so no exposure experiment could be conducted. A video showing the activities during the trial can be seen following this link.