Spatiotemporal trends in bottlenose dolphin foraging behavior and relationship to environmental variables in a highly urbanized estuary

Abstract

Marine predator foraging influences community structure and ecosystem functions, which are all linked with environmental variables. Determining variables that are associated with foraging can facilitate the identification of important habitats, which is particularly important in heavily urbanized systems. In the New York-New Jersey Harbor Estuary, bottlenose dolphinsTursiops truncatusare exposed to various stressors, including vessel activity and forthcoming offshore wind development. Here, we used passive acoustic monitoring to identify foraging conditions for dolphins from April-October of 2018-2020. When foraging, dolphins produce a series of rapid clicks (‘foraging buzzes’) which can be used as a proxy for foraging activity. We analyzed the relationship between acoustic detections of dolphins and environmental variables using a generalized additive modeling framework. The variables week, sea surface temperature (SST), and chlorophylla(chla) concentration were significantly associated with foraging activity at seasonal timescales. Foraging increased with increasing SST and water levels, with the peak of foraging occurring in autumn. The relationship between chlaconcentration and foraging was not straightforward and warrants further research. Diel foraging trends varied seasonally and annually. These results suggest that passive acoustic monitoring and environmental variables may be used to investigate marine mammal behavior and assess seasonal foraging habitat for marine predators within dynamic, heterogenous, and human-dominated environments. Baseline data on dolphin habitat use is vital given the continued expansion of anthropogenic activities and climate-driven shifts in oceanographic conditions that are occurring in this region.