Seasonal and diel variation in North Atlantic right whale up-calls: implications for management and conservation in the northwestern Atlantic Ocean

Abstract

Ship strikes are a major cause of anthropogenic mortality for the endangered North Atlantic right whale Eubalaena glacialis. Year-round data on animal presence are critical to man- aging ship strike mortality. Marine autonomous recording units were deployed throughout the Stellwagen Bank National Marine Sanctuary (SBNMS, Massachusetts Bay, USA) for 13 mo from January 2006 to February 2007 and on Jeffreys Ledge (JL, Gulf of Maine, USA) for 7 mo from November 2004 to May 2005 to determine whether passive acoustic monitoring (PAM) can improve information on right whale occurrence. Automated detection and manual review were used to determine presence and absence of right whale up-calls. In SBNMS, up-calls were detected year round, except during July and August, and calling rates were highest from January through May, peaking in April. In JL, up-calls occurred throughout all recording months, with the highest numbers from November through February. Up-calls were heard extensively in the win- tertime throughout SBNMS and JL, suggesting that these areas are important overwintering grounds for right whales. Additionally, up-calls showed a strong diel trend in both areas, with sig- nificantly more calls occurring during twilight than dark and light periods. These data indicate that right whales are present more often and over longer time periods in the western Gulf of Maine than previously thought using conventional visual techniques. Finally, this study demon- strates the utility of PAM in providing a detailed and long-term picture of right whale presence in an area that poses a significant risk of anthropogenic mortality.