Residency and movement patterns of Cuvier’s beaked whales Ziphius cavirostris off Cape Hatteras, North Carolina, USA

Hj Foley,Zt Swaim,Aj Read,Rw Baird,K Pacifici,Dl Webster

doi:10.3354/meps13593

Abstract

Cuvier’s beaked whalesZiphius cavirostrisare wide-ranging, deep-diving cetaceans that are particularly sensitive to anthropogenic noise. Current stock assessments assume a single population in the western North Atlantic Ocean, but knowledge of the residency patterns and distribution of the species is currently lacking in the region. Here we describe the spatial ecology of 20 Cuvier’s beaked whales equipped with satellite-linked tags off Cape Hatteras, North Carolina, USA, between 2014 and 2017. We applied a hierarchical switching state-space model to filter location estimates and define behavioral states of area-restricted search (ARS) and transit. We used kernel density estimation to identify high use areas, and net squared displacement analyses to assess residency. The vast majority (96%) of locations were classified as ARS behavior, suggesting that tagged whales allocated much of their time to foraging. Maximum net displacement had a sample median of 50 km, and 81% of individual whales were classified as demonstrating a resident, or ‘home range,’ movement pattern. Overall, our research indicates a localized population of Cuvier’s beaked whales occupying the area off Cape Hatteras. The tagged animals demonstrated a small, defined core use area and exhibited little displacement from the region. These patterns of movement and spatial use can inform future conservation and management of this species, which is vulnerable to anthropogenic disturbances caused by several sources, including mid-frequency active sonar and seismic exploration.

Highlights

Cuvier’s beaked whales Ziphius cavirostris are cosmopolitan members of the family of beaked whales, Ziphiidae, which frequent shelf edge and continental slope waters (Waring et al 2001, Tyack et al 2006)
To describe spatial use by Cuvier’s beaked whales, we evaluated home range and core use areas both for each individual tagged whale and for the sample of all tagged animals using utilization distributions (UDs) generated through kernel density estimation (KDE) from the hierarchical Bayesian switching statespace model (hSSSM) output
Our analysis demonstrates that Cuvier’s beaked whales are resident to the slope waters off Cape Hatteras, North Carolina, USA, over periods of at least weeks to months

Summary

Introduction

Cuvier’s beaked whales Ziphius cavirostris are cosmopolitan members of the family of beaked whales, Ziphiidae, which frequent shelf edge and continental slope waters (Waring et al 2001, Tyack et al 2006). In the western North Atlantic, the species is found in association with warm-core rings and other ephemeral oceanographic features affiliated with the Gulf Stream, leading to high densities in these areas (Waring et al 2016) Due to their response to naval mid-frequency active sonar (MFAS), which has been known to cause mass and single strandings, Cuvier’s beaked whales are of particular conservation concern (Cox et al 2006, D’Amico et al 2009, Tyack et al 2011, DeRuiter et al 2013, Simonis et al 2020). Behavioral response studies, conducted using controlled exposure experiments (CEEs) in the Bahamas, Norway, and southern California, have demonstrated that the species is sensitive to acoustic disturbance (Southall et al 2016) During these experiments, focal individuals reacted strongly to simulated sonar signals by interrupting foraging dives and moving away from the sound source, often over tens of kilometers and for several days (Tyack et al 2011). A better understanding of baseline patterns of movement and foraging ecology of Cuvier’s beaked whales could help place these behavioral responses to MFAS within an ecological context, and better define mitigation strategies for acoustic disturbances to the species throughout its range

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