Variation of ocean acoustic environments along the western North Atlantic coast: A case study in context of the right whale migration route

Abstract

Differing physical characteristics and levels of biological, environmental, and anthropogenic sounds contribute in varying levels of noise in different ocean environments. As a result, animals migrating over large ranges or widely distributed species are now exposed to a myriad of different acoustic environments, within which they must navigate, forage and reproduce. Given current increases in low-frequency (<1000Hz) anthropogenic noise, there is concern that resultant masking of communication and naturally occurring sounds may stress cetaceans already facing other forms of habitat degradation. As a critical first step to understanding the acoustic environments of coastal marine ecosystems, we examined month-long acoustic data from ten sites along the U.S. east coast that are either designated critical habitats or located along the migratory corridor of the North Atlantic right whale (Eubalaena glacialis): Gulf of Maine, Jeffreys Ledge, Massachusetts Bay, Cape Cod Bay, New York, New Jersey, North Carolina, South Carolina, Georgia (North), and Georgia (South). Data were collected using hydrophones positioned at depth to evaluate differences in the acoustic environment at these sites. High noise levels were observed at both major (New York, Boston) and non-major (Georgia) shipping ports located in or near the areas of study. Of the ten study sites, New Jersey and New York experienced the highest equivalent sound levels, while South Carolina and the Gulf of Maine presented the lowest. The majority of noise variability was found in low-frequency bands below 500Hz, including the 71–224Hz communication range utilized by long distance, contact-calling right whales and many other whale and fish species. The spatio-temporal variability of anthropogenic noise can be viewed as a form of habitat fragmentation, where inundations of noise may mask key sounds, resulting in a loss of “acoustic space” (overlapping frequency band and time of a whale's vocalization), which could otherwise be occupied by vocalizations and other acoustic cues utilized by cetaceans. This loss of acoustic space could potentially degrade habitat suitability by reducing the geographic distance across which individuals acoustically communicate, and ultimately, over long timescales, disrupt aspects related to their natural behavior and ecology. Because communication plays a vital role in the life history of cetacean species, understanding temporal and geographical differences in ambient noise as part of cetacean ecology and habitat may elucidate future conservation strategies related to the assessment of noise impacts.