Diel and tidal cycles in summer habitat use by St. Lawrence Estuary Belugas through a pluriannual passive acoustics monitoring network

Abstract

A network of 10 passive acoustics monitoring stations is used to examine patterns of habitat use at diel and tidal timescales by St. Lawrence Estuary beluga during summer 2018 and 2019. An occurrence index of vocal activity within the preferred frequency band of communications for belugas is used as a proxy for presence at the stations. Diel and tidal patterns of activity and mean residency time are extracted from statistics of hourly occurrence timeseries at the 10 stations. Spatially, diel and tidal occurrence levels of beluga communication sounds show patterns of variation that differ among the stations, but tend to be locally stable from one summer to next. Mean residency time at the 9 Estuary stations vary between 4 to 15 hours and most have an occurrence maximum during early morning. The Saguenay fjord station shows a distinct profile, with a mean residency time of 30 hours and high level of activity at evening and night. This work underlines the ability of passive acoustics, through continuous monitoring at high spatio-temporal resolution, to reveal the complexity of the habitat use by this confined marine mammal population and understand its responses to diel and tidal forcings of the ecosystem.