Rice’s whale (Balaenoptera ricei) passive acoustic detections report : August 2024 – July 2025

The Rice’s whale (Balaenoptera ricei) is the only year-round baleen whale found in the Gulf of America (formerly Gulf of Mexico), and has a population size of fewer than 100 individuals (Garrison et al., 2020). The majority of visual and acoustic detections of this endangered species occur along the northeastern shelf break near the De Soto Canyon, and some visual detections and passive acoustic recordings indicate some whales persistently occur over a broader range in the Gulf than previously thought (Debich et al., 2025a; Debich et al., 2025b; Debich et al., 2025c; Soldevilla et al., 2022a; Soldevilla et al., 2024). Rice’s whales produce stereotyped, species-specific calls that are distinct from the calls of all other baleen whales, including pulsed downsweep sequence calls, tonal longmoan calls, and constant tonal calls (Rice et al., 2014; Širović et al., 2014; Soldevilla et al., 2022b). Numerous variants of the long-moan call have been detected, with an eastern variant and multiple western variants (Soldevilla et al., 2022a). To further explore the extent of their distribution and better understand the spatio-temporal occurrence patterns of Rice’s whales, we deployed long-term passive acoustic recordings at thirteen shelf-break sites around the Gulf over one year.