Acoustic detections of North Pacific right whale Eubalaena japonica along the eastern Aleutian Chain and northern Gulf of Alaska, 2009-2023

The seasonality of Critically Endangered eastern North Pacific right whales (NPRWs) Eubalaena japonica is poorly understood in their historical foraging grounds in eastern Aleutian Islands passes (AIPs) and the northern Gulf of Alaska (NGOA). These areas are situated between designated Critical Habitat areas in the Bering Sea and the Gulf of Alaska (GOA). Here, we report passive acoustic monitoring results for NPRWs from 6 sites—2 in the AIPs (2009-2023) and 4 in the NGOA (2019-2023). All data (64235 h) were manually processed for NPRW vocalizations; results are presented as daily calling activity (CA Daily ; the percentage of 10 min recordings per day with detections). NPRWs occurred at all sites and in the majority (84%) of sampled calendar years. Across sites, variable detections suggest seasonality in occurrence and habitat use. The presence of summer (Jun-Aug) peaks in calling at most sites indicates that these areas are contemporary feeding grounds. The greatest, most consistent CA Daily occurred in the GOA right whale Critical Habitat in fall months (~Sep-Dec) concurrent with NPRW presence in the Bering Sea. The timing of overwinter (~Dec-May) detections at AIP sites relative to the Bering Sea detections supports their use as a migratory corridor. Seasonal CA Daily along the GOA sites does not support an NPRW coastal migratory route, although sampling limitations may obscure underlying migratory trends. Overall, these results offer new seasonal insights into right whale occurrences in 2 key conservation areas.