Time-space distribution of North Atlantic Right Whale in Gulf of St. Lawrence from acoustic monitoring between 2010 and 2022

Abstract

Recordings from the passive acoustic monitoring (PAM) network deployed in the Estuary and Gulf of St. Lawrence for detecting marine mammals and assessing ocean noise are analyzed to extract the time-space pattern of habitat use by North Atlantic right whale (NARW) from 2010 to 2022. Data from an ensemble of 24 027 days of observation, recorded at 12 seafloor PAM stations and 8 ocean observing (OOS) buoys, were processed to detect NARW upcalls using an artificial intelligence (AI) algorithm previously developed for this ecosystem. NARW occurrences in this marginal inland sea of the Northwest Atlantic during the ice-free period, shifted in 2015 from occasional to frequent. High occurrence levels were maintained since. Although NARW upcalls were detected over a large part of the Gulf, they were very rare out of the southern Gulf shelf and north-northwest of Anticosti Island. Excluding rare presence events, the average occurrence season began at the end of April and ended at the beginning of December. The majority of annual occurrences (90% of occurrence days) was between 5 June and 2 November. The NARW occurrences into the Gulf from our PAM network culminated in mid-August. The established general spatial pattern then persisted until November. It comprised two main areas: the Southwestern shelf of the Gulf of St. Lawrence, where most of the occurrences were observed, and the area north-northwest of Anticosti Is., where the occurrence levels were lower. The occurrences in Shediac trough dominated throughout the season. Variability of occurrences at the stations within and between season was common. The proportion of seasonal occurrence in the Gulf throughout the season is analyzed to infer the seasonal mean pattern of NARW incursion and retreat, and to extract relevant dates for NARW protection and management decisions.