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Acoustic monitoring for baleen whale vocalizations off southern Oman, 2020 to 2022
Salvatore Cerchio, Andrew Willson, Danielle Cholewiak, Meredith Sackett, Suaad Al Harthi, Robert Baldwin, Tim Collins, Gianna Minton, Maia Sarrouf Willson
Paper SC/69A/CMP/12/Rev1 reports on acoustic monitoring for blue whales and other baleen whales off the southern coast of Oman, funded in part by the IWC SC in 2020. Autonomous acoustic recorders were deployed in deep continental slope waters off Ras al Hasik, Dhofar, in southern Oman during the period November 2020 to April 2022, in a region were humpback whales, blue whales and Bryde’s whales have been documented on boat surveys, and previous acoustic monitoring from the shelf has described the temporal distribution of humpback whale song and NWIO song attributed to blue whale. In addition to humpback song, four different songs/vocalizations were detected throughout the recording period, including NWIO song, CIO (Sri Lanka) blue whale song, and two vocalizations that have not been attributed to species, one of which (dubbed Long-107Hz) is novel and previously unreported. While NWIO song was the most extensively documented, the presence of CIO song raises the possibility that the blue whales off Oman might belong to the CIO/Sri Lanka acoustic population, and that NWIO song may instead be attributed to Bryde’s whales. Alternatively, the current hypothesis that NWIO song and CIO song represent two different acoustic populations may be correct, indicating that the two populations’ ranges overlap in southern Oman, and the novel vocalization may be attributed to Bryde’s whales. Further research is recommended to distinguish between these scenarios. Humpback whale song was documented during the boreal winter breeding season, however at dramatically reduced frequency of occurrence as compared to the previous acoustic monitoring in 2011/2012. These data imply a potential distribution shift of the Arabian Sea humpback whale population, as also suggested in SC/69A/CMP/XX from visual survey data.
he waters off the coast of Oman have been documented as habitat for endangered populations of Arabian Sea humpback whales (ASHW), North Indian Ocean blue whales, and two poorly studied populations of Bryde’s whales. In order to assess the population identity and presence of baleen whales off southern Oman, autonomous acoustic recorders were deployed in deep continental slope waters off Ras al Hasik, Dhofar, during the period March 2020 to April 2022, with an approximately one-year gap in recording effort between October 2020 and November 2021 due to malfunction of equipment. Humpback whales, blue whales and Bryde’s whales have all been sighted during boat surveys in this region, and previous acoustic monitoring from the shelf has described the temporal distribution of humpback whale song and the putative Northwest Indian Ocean (NWIO) blue whale song. In these recent deployments humpback whale song was documented during the boreal winter breeding season in 2020 (late season only) and 2022, however at dramatically reduced frequency of occurrence compared to the previous acoustic monitoring in 2011/2012. These data imply a potential distribution shift of the Arabian Sea humpback whale population, as also suggested from the absence of ASHW sightings in the same area during boat surveys in March 2021.