PROJECTS

Twenty-seven embarks were conducted between 2010 and 2019, mostly on destroyer class ships. A total of 716 sightings of individual animals or groups were recorded across all embarks, of which, 544 sightings of cetaceans were used in the analysis.

Relatively small sample sizes prevented analysis at the individual species level so the data were divided into 4 groups based on similarity of surfacing patterns and detectability: 1) rorquals (i.e. large baleen whales); 2) sperm whales; 3) small cetaceans in small groups (6 or less); and 4) small cetaceans in large groups (more than 6). The analysis focused on the probability of an individual or group entering specified mitigation ranges undetected. For each species group, the probability of going undetected was estimated at 200 yards, 500 yards, and 1,000 yards for both the MMOs and the Navy LT.  These distances are based on the mitigation zones that are applied for mid-frequency active sonar during training and testing activities. The probability of an animal or group of animals remaining undetected was generally higher for the LT than for MMOs at all distances. Probability of remaining undetected also increased with distance from the ship for both the LT and MMOs. Rorquals were more likely to be detected than sperm whales due to their differing dive patterns, and small cetaceans in large groups were slightly more likely to be detected than small cetaceans in small groups when sighted within 200 yards from a ship.