Foraging behavior of Critically Endangered North Atlantic right whales is associated with ambient noise, prey density, and the acoustic behavior of conspecifics

Abstract

The endangered North Atlantic right whale (NARW) faces threats from lethal and sublethal stressors. Prey limitation has been linked to reduced growth and fecundity, while anthropogenic noise has been associated with acoustic behavior changes and increased physiological stress. We combined disparate data sets collected in Cape Cod Bay, Massachusetts, USA, across multiple years, quantifying links between prey, calling behavior, noise, and foraging behavior to answer 3 questions: (1) What are the characteristics of noise and prey density in the patches where NARW forage? Are prey density, call rate, and noise related to (2) the probability of being in a foraging state and (3) the size of the foraging group? We found links between predicted prey density and 2 measures of NARW foraging: probability of being in a foraging state and foraging group size. There were also significant non-linear relationships between lagged calling behavior and these same measures. For group size, an interaction term between calling behavior and prey density suggested a complex interrelationship between these variables. When more ambient noise was measured near a patch in the 4 h prior to a sighting of foraging whales, whales foraged in lower-quality zooplankton patches. Elevated noise ahead of aggregated sightings was also associated with a smaller group size. This is consistent with the hypothesis that increased ambient noise disturbs foraging and/or reduces communication space, limiting the ability of NARWs to fully exploit their environment. Our findings suggest pathways for future experiments to explicitly test the mechanisms underpinning foraging processes in endangered NARW.