Mid-summer fin whale ( Balaenoptera physalus ) call rate and repertoire in Southern New England

Acoustic behavior of endangered western North Atlantic fin whales has been interpreted from passive acoustic monitoring and surface observations, but we lack fine-scale, high-fidelity individual data. In July and August 2023 and 2024, we deployed 29 acoustic biologging tags on fin whales in southern New England. From drone imagery and PCR, we identified the individuals (n = 23) as mostly male (n = 22). Over 137.5 h of data, individual tagged whales called at a very low rate (0.8 + /− 2.0 calls/h). We classified the movement data into five behavioral states (feeding, exploratory foraging, travel, rest, and unknown). Whales called the most during nighttime feeding. Nine males called during data collection (mean = 20 calls (1–132)), from which we identified eight distinct call types. Downsweeps centered at 40 Hz were a significantly larger proportion of the traveling call repertoire (24%) than when considering all states together (8.8%). These results support the hypothesis that fin whales call to coordinate foraging in this region during mid-summer. Low, variable call rates demonstrate the potential for missed detections of this endangered population by passive acoustic monitoring stations offshore of the U.S. East Coast.