Seasonal calling and acoustic masking in gray ( Halichoerus grypus ) and harbor ( Phoca vitulina ) seals in the Northwest Atlantic

This project investigates the seasonal calling behavior of gray (Halichoerus grypus) and harbor (Phoca vitulina) seals in the Northwest Atlantic (NWA), the potential for acoustic competition between species, and acoustic masking associated with anthropogenic noise. While the phenology of harbor seal roars is well documented, the same is not true for sympatric gray seals. In the NWA, increasing spatial competition associated with rapid gray seal range expansion may manifest acoustically. We investigated the presumed breeding phenology of gray seals at Duck Island, ME—a recently recolonized, potential breeding site—and compared the timing of their vocalizations with those of harbor seals. Our objectives were to assess (1) temporal overlap, (2) patterns of use, and (3) overlap of seasonal vessel traffic with phocid calling activity. Initial results from the 2024 breeding season indicate that gray seal calling peaked on January 11 and occurred primarily at night. Harbor seal calling peaked on July 1, also predominantly at night. Vessel noise levels were highest in summer, suggesting potential acoustic masking of daytime harbor seal calls. Strong seasonal stratification in calling activity may reduce interspecific acoustic competition and suggest resilience to shared soundscapes in a changing acoustic environment.