Passive acoustic monitoring on the North Atlantic right whale calving grounds

Abstract

North Atlantic right whales Eubalaena glacialis calve during winter off Florida and Georgia, USA, a region of high shipping traffic, and ship-strike risk is a concern. Passive acoustic monitoring (PAM) of right whales on their foraging grounds increases detection opportunities to inform mariners of right whale presence and reduce the likelihood of ship strike. This study evaluates the effectiveness of PAM on right whale calving grounds by documenting the occurrence of right whale call detections on 2 types of acoustic instruments deployed off the coasts of Savannah, GA, and Jacksonville, FL, and comparing results with visual sightings and ambient noise conditions. Over 400 right whale calling events were detected on archival marine acoustic recording units (MARUs) at 2 sites across 2 seasons, and 92% of these calling events included right whale upcalls. Daily detections on archival MARUs and near-real time Autobuoys, which automatically detect upcalls, were significantly correlated and occurred on up to 25% of days off Savannah and 46% of days off Jacksonville. Visual aerial surveys detected right whales within 20km of each acoustic site on a similar proportion of days with visual survey effort (15 to 33% off Savannah and 34 to 43% off Jacksonville). Acoustic methods enabled greater temporal effort, yielding a 2- to 10-fold increase in days with right whale detections over visual methods. Shipping noise and fish chorusing likely mask right whale call detections. However, considering the high number of right whale calling event detections by PAM during this study the results indicate that this is an effective method to augment detection of right whales in this environment, especially at night when they cannot be seen.