Cetaceans and vessels overlap assessment within a migration corridor using passive acoustic monitoring

Migratory cetaceans travel from feeding grounds in summer to mating and calving grounds in winter, and consequently, significant efforts are made to protect those grounds. However, areas along the migration corridors also play a significant role in cetacean ecology since many important activities occur in between those grounds. The increase of anthropogenic pressure in those intermediate areas creates the need to assess cetacean habitat use and overlap with human activities. The Cerralvo Channel in the Gulf of California, Mexico is a clear example of such areas. In this study, bimonthly passive acoustic monitoring during the cold season (November 2022 -May 2023) provided information on the presence, diel-pattern and vessel and cetacean overlap in the area. Migratory blue whales, fin whales, Bryde’s whales, sperm whales and dolphins (Delphinidae) were detected. Based on the type of calls it was found that besides transit, blue whales might also use the area for breeding and feeding. For the other species, important activities such as feeding, socializing and probably breeding also take place in the channel. Out of 200 h recordings, vessels were detected during 91 h, cetaceans during 80 h, and both overlapped during 30 h. Although vessels were detected for 45.5 % of the time of all recordings, the overlap time was relatively low (15 %). However, given the increase in tourist activities in the area, continuous monitoring is recommended to identify potential threats to cetaceans.