Acoustic detection of North Pacific right whales in a high-traffic Aleutian Pass, 2009-2015

ABSTRACT: Little is known about the winter distribution of the Critically Endangered eastern population of North Pacific right whale Eubalaena japonica (NPRW), but it has been proposed that the eastern Aleutian Islands, specifically Unimak Pass, constitute a plausible migratory route for individuals. This is a major point of concern given the high shipping traffic in this pass. Therefore, a long-term acoustic recorder was deployed in Unimak Pass (2009-2015), and NPRWs were identified using the ‘up’ and ‘gunshot’ call types during manual review of data (8188 recorded hours). Calls were grouped into periods of hypothesized migration (Dec-Feb and Mar-May) and other (Jun-Aug and Sep-Nov). Overall, NPRW calling was intermittent and clustered in time, suggestive of a few individuals transiting the area across seasons. Upcalls (n = 31) were detected on 7 d and occurred most often during Dec-Feb, whereas gunshots (n = 465) were detected on 32 d, occurring in all months except February and October. The majority of individual gunshot calls (n = 306) occurred over 3 d in Dec-Feb 2014-15. Because of this pattern, gunshot calling occurred on more days during Jun-Aug, while more individual calls occurred during Dec-Feb. Diel and seasonal trends in hourly call detection rates were absent. Together, these data confirm that NPRW use Unimak Pass both during and outside of the assumed migratory period. Pervasive vessel noise throughout the study highlights near constant potential for interaction with anthropogenic disturbance. Consistently higher vessel noise during Dec-Feb suggests that this species is most vulnerable during the assumed migratory period.