CIVINS / Blainville's beaked whales (Mesoplodon densirostris) use broadband, ultrasonic echolocation signals (27 to 57 kHz) to search for, localize, and approach prey that generally consist of mid-water and deep-water shes and squid. Although it is well knownthat the spectral characteristics of broadband echoes from marine organisms are a strong function of size, shape, orientation and anatomical group, little is known as to whether or not these or other toothed whales use spectral cues in discriminating between prey and non-prey. In order to study the prey-classification process, a stereo acoustic tag was mounted on a Blainville's beaked whale so that emitted clicks and corresponding echoes from prey could be recorded. A comparison of echoes from prey selected by the whale and those from randomly chosen scatterers suggests that the whale may have, indeed, discriminated between echoes using spectral features and target strengths. Specifically, the whale appears to have favored prey with one or more deep nulls in the echo spectra as well as ones with higher target strength. A three-dimensional, acoustic scattering model is also developed to simulate broadband scattering from squid, a likely prey of the beaked whale. This model applies the distorted wave Born approximation (DWBA) to a weakly-scattering, inhomogeneous body using a combined ray trace and volume integration approach. Scatterer features are represented with volume elements that are small (less than 1/12th of the wavelength) for the frequency range of interest (0 to 120 kHz). Ranges of validity with respect to material properties and numerical considerations are explored using benchmark computations with simpler geometries such as fluid-filled spherical and cylindrical fluid shells. Modeling predictions are compared with published data from live, freely swimming squid. These results, as well as previously published studies, are used in the analysis of the echo spectra of the whale's ensonified targets. / CIVINS

Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2006. / "September 2006." Bibliography: p. 89-96.

Underwater gliders can provide an alternative cost-effective platform for passive acoustic monitoring surveys, compared to boat surveys, for abundance estimation and to collect high resolution environmental data for habitat studies. Gliders are usually equipped with one acoustic sensor, which limits the methods available for abundance estimation from acoustic data. Estimation of parameters used in distance sampling methodology, such as the detection function and cue rates, must be estimated separately from the glider deployment. A methodology for deriving the acoustic detection function of vocal animals is demonstrated in chapter 2 with a combined biologging and passive acoustic experiment. The methodology consists of distance estimation of the clicks produced by the tagged animal and detected at acoustic receivers placed at different depths, using surface bounce detections to estimate range. In addition, different detection algorithms were tested for the detectability of Blainville's beaked whales. Detectability was found to vary with depth for Blainville's beaked whales in the area of El Hierro (Canary Islands). The depth dependent detectability for this species was tested further in chapter 3 with a wider dataset from two different geographic populations of Blainville's beaked whales, those of El Hierro and the Bahamas. Differences in detectability were found using depth and animal movement data as recorded on the DTAG in a simulated network of receivers placed at different depths. In addition, sequences of clicks, called click scans, were tested as an additional “cue” for cue counting methodology. The high directionality of beaked whale regular clicks leads to reduced detection ranges for receivers close to the surface or for receivers placed much deeper than the foraging depths of the wales and this reduction translates into varying lengths and numbers of detected click clusters as a function of distance and receiver depth. Chapter 4 presents a method for estimating density of animals from underwater gliders and tests the method in a simulated glider survey using different distribution and density scenarios using clicks and click scans as cue for density estimation.

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 89-96). / Blainville's beaked whales (Mesoplodon densirostris) use broadband, ultrasonic echolocation signals (27 to 57 kHz) to search for, localize, and approach prey that generally consist of mid-water and deep-water fishes and squid. Although it is well known that the spectral characteristics of broadband echoes from marine organisms are a strong function of size, shape, orientation and anatomical group, little is known as to whether or not these or other toothed whales use spectral cues in discriminating between prey and non-prey. In order to study the prey-classification process, a stereo acoustic tag was mounted on a Blainville's beaked whale so that emitted clicks and corresponding echoes from prey could be recorded. A comparison of echoes from prey selected by the whale and those from randomly chosen scatterers suggests that the whale may have, indeed, discriminated between echoes using spectral features and target strengths. Specifically, the whale appears to have favored prey with one or more deep nulls in the echo spectra as well as ones with higher target strength. A three-dimensional, acoustic scattering model is also developed to simulate broadband scattering from squid, a likely prey of the beaked whale. / (cont.) This model applies the distorted wave Born approximation (DWBA) to a weakly-scattering, inhomogeneous body using a combined ray trace and volume integration approach. Scatterer features are represented with volume elements that are small (less than 1=12th of the wavelength) for the frequency range of interest (0 to 120 kHz). Ranges of validity with respect to material properties and numerical considerations are explored using benchmark computations with simpler geometries such as fluid-filled spherical and cylindrical fluid shells. Modeling predictions are compared with published data from live, freely swimming squid. These results, as well as previously published studies, are used in the analysis of the echo spectra of the whale's ensonified targets. / by Benjamin A. Jones. / S.M.

Beaked whales are comparatively unknown social mammals due to their deep-ocean distribution and elusive habits. The deep-ocean is the largest biome on Earth and the final frontier for human expansion. Since their first discovery, beaked whales have remained largely hidden from science. In this era of rapid technological advancement, genetic and genomic methods are key tools for population biologists and are particularly useful in describing rarely seen species. Using DNA-barcoding and nuclear markers, the publications in this thesis provide data on the distribution and external appearance of two species of beaked whale: the spade-toothed (Mesoplodon traversii) and Derinayagala’s whale (Mesoplodon hotaula). These whales were previously known from only a handful of tissue and bone specimens. Long-term efforts have facilitated the collection of samples of Gray’s beaked whale (Mesoplodon grayi) and we have used shot-gun sequencing to characterise the mitochondrial genome and isolate species-specific nuclear microsatellite loci. Using genetic species and sex identification, together with museum specimens and multivariate analyses, we provide clear evidence of sexual dimorphism in cranial dimensions and geographic variation in external morphology. No genetic differentiation was evident in Gray’s beaked whales across a large study area (~ 6,000 km). With a large female effective population size (Ne) and genetic homogeneity, we hypothesise that gene flow is facilitated by large-scale oceanographic features, such as the sub-tropical convergence. Genetic kinship analyses within Gray’s beaked whale groups suggest that the whales that strand together are not related. Both sexes disperse from their parents and these groups are not formed through the retention of kin. These results are consistent with a ‘fission-fusion’ social system that has been observed in some oceanic dolphin species. Taken together, these data provide the first insights into the population dynamics, dispersal and social organisation in Gray’s beaked whales. These publications highlight the value of using genetics alongside other techniques to describe inter- and intraspecific diversity. For beaked whales, the dead can tell us much about the living.

Les cétacés grands plongeurs, cachalots Physeteridae et Kogiidae, et baleines à bec Zipiidae, sont des espèces marines rares. Leur faible densité, aire de distribution étendue et faible disponibilité en surface génèrent de faibles taux d’observations. Cette particularité constitue un défi pour la modélisation d’habitat de ces espèces, préalable à leur conservation. Les modèles doivent gérer l’abondance de zéros qui limitent leur capacité à inférer des résultats écologiquement cohérents. Cette thèse vise donc à trouver une méthodologie adaptée aux jeux de données abondants en zéros, à déterminer comment les variables environnementales influencent la distribution des grands plongeurs et à prédire les zones potentielles qu’ils utilisent. Tester la capacité de prédiction de différents modèles d'habitat confrontés à un nombre décroissant d’observations a permis de souligner la pertinence d’un modèle, même si un minimum de 50 observations est nécessaire pour fournir des prédictions fiables. Des données issues de différentes campagnes visuelles ont été assemblées afin de produire les premières cartes de densités de grands plongeurs à l’échelle de l’océan Atlantique Nord et la mer Méditerranée. Les densités les plus élevées sont prédites dans les eaux entre 1500 et 4000 m de profondeur et près des fronts thermiques, particulièrement le long des pentes continentales et à l'ouest de l'océan Atlantique Nord. Par ailleurs, l’analyse de la transférabilité des modèles a montré une variation des habitats préférentiels en fonction des écosystèmes. Finalement, cette thèse permet de discuter les défis de la modélisation statistique appliquée aux espèces rares et les applications de gestion associées. / Deep-diving cetaceans, sperm- and beaked whales Physeteridae, Kogiidae and Ziphiidae, are rare marine species. Due to their low densities, wide distribution ranges and limited presence at the water surface, visual surveys usually result in low sighting rates. This paucity of data challenges the modelling of their habitat, prerequisite for their conservation. Models have to cope with a great number of zeros that weakens the ability to make sound ecological inferences. Consequently, this thesis aimed at finding a methodology suitable for datasets with a large number of zeros, determining how environmental variables influence deep-diver distributions and predicting areas preferentially used by these species. By testing the predictive performance of various habitat models fitted to decreasing numbers of sightings, I selected the most suitable model and determined that at least 50 sightings were needed to provide reliable predictions. However, individual surveys can rarely provide sufficient deep-diver sightings thus I merged many visual survey datasets to produce the first basin-wide deep-diver density maps in the North Atlantic Ocean and the Mediterranean Sea. Highest densities were predicted in waters from 1500-4000 m deep and close to thermal fronts ; hotspots were predicted along the continental slopes, particularly in the western North Atlantic Ocean. In addition, a model transferability analysis highlighted that habitat drivers selected by the models varied between contrasted large ecosystems. Finally, I discussed challenges related to statistical modelling applied to rare species and the management applications of this thesis.