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Age-specific behavior and habitat use in humpback whales: Implications for vessel strike

Julia E. F. Stepanuk*, Eleanor I. Heywood, Jennifer F. Lopez, Robert A. DiGiovanni Jr. , Lesley H. Thorne

*Corresponding author:

ABSTRACT: Vessel strikes are a major threat impacting large whales globally. Juvenile whales often represent a high proportion of lethal vessel strikes, but few studies have investigated whether juvenile whales show different behaviors that might influence their risk of vessel strike. We evaluate how variability in habitat use and foraging behavior by age class influences the risk of vessel strike for humpback whales (Megaptera novaeangliae) in the New York Bight (NYB), a highly urbanized region with frequent vessel strikes. We used data from unmanned aerial vehicle (UAV) surveys to compare the habitat use and foraging behavior of adult and juvenile humpback whales and also compared length measurements of foraging individuals with those of detected animals killed by vessel strikes. Further, we analyzed the speed and density of vessel traffic relative to humpback whale habitat use using Automatic Information System data. The vast majority (93%) of humpback whales confirmed to have been struck by vessel strikes in the NYB were juveniles. Whales foraging in nearshore waters were exclusively juveniles that were surface feeding, while both juveniles and adults foraged cooperatively in offshore waters. Passenger vessel density and speed were highest in nearshore waters. The habitat use and surface foraging behavior of juvenile humpback whales may make them particularly vulnerable to vessel strike in nearshore waters and passenger vessels in these waters may be a risk factor. This work highlights the importance of understanding age-specific differences in habitat use to better understand and mitigate the risk of anthropogenic threats for large whales.