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

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 evaluated 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 compared length measurements of foraging individuals with those confirmed to have been killed by vessel strikes. Further, using Automatic Information System data, we analyzed the speed and density of vessel traffic relative to humpback whale habitat use. The vast majority (93%) of humpback whales confirmed to have been struck by vessels 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 strikes 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 to large whales.

Site fidelity, population identity and demographic characteristics of humpback whales in the New York Bight apex

“…Thus, it is conceivable that the young age of individuals in the NYBA may have biased matches toward the GoM considering the extensive effort employed there to catalogue whales from the year of birth. The young age structure in the nearshore waters of the NYBA is consistent with recent work by Stepanuk et al (2021) in the greater New York Bight, and as described by Swingle et al (1993), Barco et al (2002) and Aschettino et al (2020) for live whales from the USMA. It is also consistent with the primary age-class of stranded humpback whales found in the USMA from 1985-2000 (Wiley et al, 1995;Barco et al, 2002) and whales catalogued in the NYBA that were found stranded.…”

“…Extended occupancy in the NYBA has the potential to increase individual overlap with human activities. Increasing sightings in and around shipping lanes in the New York Bight and greater USMA (Brown et al, 2019;Aschettino et al, 2020;King et al, 2021;Stepanuk et al, 2021;Zoidis et al, 2021;Smith et al, 2022) may be a significant factor in the latest Unusual Mortality Event for humpback whales along the Atlantic Coast. The recent designation of several Wind Energy Areas within the New York Bight (BOEM, 2021) will inevitably lead to an increase in vessel traffic (Dolman & Simmonds, 2010).…”

Pairing AIS data and underwater topography to assess maritime traffic pressures on cetaceans: Case study in the Guadeloupean waters of the Agoa sanctuary

“…However, it is unlikely that cetaceans respond linearly and uniformly between and among species (e.g. differential species and age-class vulnerability to each pressure, such as mother and calf known to be particularly vulnerable to speed) to an increase in the pressure score (Stepanuk et al, 2021). Research and empirical data are therefore needed to refine the maps by better characterising species responses to single maritime traffic pressures and to cumulative pressures.…”

Integrating 3D models with morphometric measurements to improve volumetric estimates in marine mammals

“…Morphometric measurements of humpback whales were collected in the New York Bight using a DJI Phantom Pro+ (V1.0) UAV. UAV flights and detailed methods for obtaining morphometric measurements in cm are described in Stepanuk et al (2021). We obtained measurements of total body length (TL) and body widths at 5% intervals along the body axis of the whale (Figure 1a) using the open‐source platform MorphoMetriX (Torres & Bierlich, 2020) and summarized the output data for all individuals into a single output file using CollatriX (Bird & Bierlich, 2020).…”

“…Detailed instructions for model-building and scripts for scaling and estimating volume are archived on GitHub at https://github.com/natha n-hirtl e/humpb ack_3dm.git. measurements in cm are described in Stepanuk et al (2021). We obtained measurements of total body length (TL) and body widths at 5% intervals along the body axis of the whale (Figure 1a) using the open-source platform MorphoMetriX (Torres & Bierlich, 2020) and summarized the output data for all individuals into a single output file using CollatriX (Bird & Bierlich, 2020).…”