Rice’s whale occurrence in the western Gulf of Mexico from passive acoustic recordings

Abstract

Rice's whales (Balaenoptera ricei) are one of the most endangered marine mammal species in the world. Their known distribution is restricted to the Gulf of Mexico (GoMx) and basic knowledge of their ecology is limited. In their core distribution area along the northeastern GoMx shelf break (Rosel & Garrison, 2021), their abundance was estimated at 51 individuals, 95% CI [20, 130], based on line transect surveys conducted during 2017 and 2018 (Garrison et al., 2020). Most Rice's whale sightings and acoustic detections during the last 30 years occur in this area off the northwestern coast of Florida (Rice et al., 2014; Rosel et al., 2021; Širović et al., 2014; Soldevilla et al., 2017; Soldevilla, Ternus, et al., 2022). While visual sightings are rare (e.g., Rosel et al., 2021), recent passive acoustic detections during one year of recordings (Soldevilla, Debich, et al., 2022) establish that they routinely occur along the shelf break of the northwestern GoMx off Louisiana as well. Currently, Rice's whales are only known to occur within U.S. waters of the northern GoMx, although whaling records (Reeves et al., 2011) suggest they were distributed more broadly across the GoMx historically. Understanding their range and distribution is important for evaluating the impacts of human activities, including climate change, that threaten their long-term survival. Considering the high levels of anthropogenic activity throughout the GoMx (e.g., oil and gas exploration and extraction, fisheries, shipping, and oil spills), a comprehensive knowledge of the current distribution of Rice's whales is needed to understand the risk of these activities to the whales and to develop effective recovery and conservation strategies for this endangered species (Rosel et al., 2016).