The Relationship among Oceanography, Prey Fields, and Beaked Whale Foraging Habitat in the Tongue of the Ocean

and Beaked Whale Foraging Habitat in the Tongue of the Ocean. PLoS ONE 6(4): e19269. doi:10.1371/journal.pone.0019269 The Relationship among Oceanography, Prey Fields, and Beaked Whale Foraging Habitat in the Tongue of the Ocean Elliott L. Hazen 0 Douglas P. Nowacek 0 Louis St. Laurent 0 Patrick N. Halpin 0 David J. Moretti 0 Howard Browman, Institute of Marine Research, Norway 0 1 Duke University Marine Lab, Beaufort, North Carolina, United States of America, 2 Joint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu, Hawaii, United States of America, 3 Pacific Fisheries Environmental Lab, National Oceanic and Atmospheric Association, Pacific Grove, California, United States of America, 4 Pratt School of Engineering, Duke University , Durham , North Carolina, United States of America, 5 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, United States of America, 6 Naval Undersea Warfare Center , Newport, Rhode Island , United States of America Beaked whales, specifically Blainville's (Mesoplodon densirostris) and Cuvier's (Ziphius cavirostris), are known to feed in the Tongue of the Ocean, Bahamas. These whales can be reliably detected and often localized within the Atlantic Undersea Test and Evaluation Center (AUTEC) acoustic sensor system. The AUTEC range is a regularly spaced bottom mounted hydrophone array covering .350 nm2 providing a valuable network to record anthropogenic noise and marine mammal vocalizations. Assessments of the potential risks of noise exposure to beaked whales have historically occurred in the absence of information about the physical and biological environments in which these animals are distributed. In the fall of 2008, we used a downward looking 38 kHz SIMRAD EK60 echosounder to measure prey scattering layers concurrent with fine scale turbulence measurements from an autonomous turbulence profiler. Using an 8 km, 4-leaf clover sampling pattern, we completed a total of 7.5 repeat surveys with concurrently measured physical and biological oceanographic parameters, so as to examine the spatiotemporal scales and relationships among turbulence levels, biological scattering layers, and beaked whale foraging activity. We found a strong correlation among increased prey density and ocean vertical structure relative to increased click densities. Understanding the habitats of these whales and their utilization patterns will improve future models of beaked whale habitat as well as allowing more comprehensive assessments of exposure risk to anthropogenic sound. - Funding: The data collection and analysis was funded by the Office of Naval Research as N00014-08-1-1162. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Beaked whales are one of the least understood marine mammal taxa in the worlds oceans, particularly the Mesoplodon genera, all of which are listed as data deficient under the IUCN red list [1]. Due to their incredibly long and deep dives (e.g. . 50 minutes and 1000 meters), they have been extraordinarily difficult to study using typical visual techniques [2,3]. Moreover, while Mesoplodon species are found in most of worlds oceans, they are often distributed offshore necessitating the use of large ships to study their behavior and distribution [3]. Testament to the difficulty in studying them, ecological studies have been able to focus on little more than data from stranded animals, e.g. diet from stomach contents [4]. Beaked whale species also appear to be particularly sensitive to mid-frequency sonar as a number of mass strandings have occurred coincident with naval exercises [5]. The lack of information on beaked whale ecology has made assessing the potential risk from anthropogenic activity much more difficult. Recent research using short-duration tags around oceanic islands (i.e., where deep waters are close to shore) has provided valuable and insightful data on diving behavior, beaked whale echolocation, and identifying beaked whale prey [6,7,8]. Vessel surveys along the western side of Abaco Island, Bahamas and in the Tongue of the Ocean have established what may be a resident population of Blainvilles beaked whales inhabits these waters [3,9]. The Tongue of the Ocean (TOTO) is a deep-water basin approximately 204 kilometers long and 36 kilometers wide and varying in depth from 12802010 meters. The semi-enclosed nature of the TOTO makes it an ideal study site as it contains bathymetric features that include known habitat for Blainvilles beaked whales. The TOTO is especially conducive for studying beaked whales because it is home to a large bottom-mounted hydrophone array that is part of the Atlantic Undersea Test and Evaluation Center (AUTEC). Moored hydrophones have been commonly used to understand patterns of vocal animals across a range of temporal scales (e.g. daily, monthly, seasonal [10]). Blainvilles beaked whales have very regular and predictable interclick intervals making species identification possible from an acoustic recording [2,11]. Foraging click trains have been detected successfully using a combination of manual and automated methods from moored hydrophones in the TOTO [12,13]. Deep scattering layers (DSLs) serve as an important prey resource for top predators, particularly in oligotrophic oceanic habitats [14,15,16] and their vertical migration may serve as an important source of mixing in the ocean [17]. The composition of species in deep scattering layers is diverse and can change both temporally and spatially requiring multiple samples and sampling gear [18,19,20,21]. The functional groups comprising DSLs include myctophid fishes and squid, both of which are known to be prey items of Blainvilles beaked whales [4,8]. Traditional net tows give limited information on depth distributions and average biomass throughout the length of a trawl but allow measurements and species identification of sampled organisms. In contrast, fisheries acoustics offer a minimally invasive approach to measure sound scattering organisms and to provide an acoustic density of prey. When possible, trawl samples can be used to ground truth the acoustically detected organisms including length frequency distributions and species compositions [22]. Acoustic data in the absence of trawls can still provide a relative measure of prey distribution [19,23] that may help inform models of top predator distribution. Habitat models are a valuable tool that can help identify factors structuring organismal distribution, abundance, and even behavior [24]. In addition, habitat models are a valuable tool for identifying critical habitat and assembling spatial management strategies for highly mobile species [25]. Habitat models for beaked whales have been created in the Bahamas, eastern tropical Pacific, and Hawaiian islands though most have focused o (...truncated)