Getting below the surface : density estimation methods for deep diving animals using slow autonomous underwater vehicles

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

Distribution and abundance estimation of sperm whales (Physeter macrocephalus) along the Hellenic Trench in eastern Mediterranean

Sperm whales (Physeter macrocephalus) of the Hellenic Trench, Mediterranean Sea, illustrate a constant summer distribution and abundance. The sperm whale population of the Mediterranean Sea has been characterized as “Endangered” by the IUCN (2012) although areas of high occurrence should be under a wider conservation planning. Here, I modelled sperm whale distribution in the Hellenic Trench in order to quantify the distribution of the sperm whale along the Hellenic Trench. To do this a combined method of GAMs-GEEs were used to account for the autocorrelation existed in the data. Social groups and solitary or loosely aggregated males varied significantly in the habitat use within the study area, with males using habitat closer to the shore and social groups to present an affinity for higher Sea Surface Temperature (SST) and Sea Level Anomaly (SLA) values. The covariates remained in the model for the combined dataset (social groups-males) are depth, seabed steepness and distance from the shore, distance from 1km depth contour, SST and SLA. Point transects sampling was used for the abundance estimation of the summer sperm whale population from a combined acoustic and visual survey and an estimate of 27 [19.7, 32.08] individuals was derived with 95% CI. An acoustic detection function was modelled with a Generalized Linear Model (GLMs) with data derived from an experimental dataset. The detectability of sperm whales was influenced by group size, so stratification sampling was applied to take into account the bias introduced by the number of individuals in each group. An acoustic effective range of 13 – 21 km was derived, with bigger sized groups being detected at greater distances than the smaller ones. The Hellenic Trench presents apparently an important area for the sperm whale sub-population of the Mediterranean Sea. The Hellenic Trench has been recommended to be an MPA for the protection of the sperm whale by ACCOBAMs (Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic Area)

Sperm whales exhibit variation in echolocation tactics with depth and sea state but not naval sonar exposures

Auditory masking by anthropogenic noise may impact marine mammals relying on sound for important life functions, including echolocation. Animals have evolved antimasking strategies, but they may not be completely effective or cost-free. We formulated seven a priori hypotheses on how odontocete echolocation behavior could indicate masking. We addressed six of them using data from 15 tagged sperm whales subject to experimental exposures of pulsed and continuous active sonar (PAS and CAS). Sea state, received single-pulse sound exposure level (SELsp), whale depth and orientation towards surface, and sonar were considered as candidate covariates representing different masking conditions. Echolocation behavior, including buzz duration and search range, varied strongly with depth. After controlling for depth and angle to the surface, the likelihood of buzzing following a click train decreased with sea state (t = −7.3, p < .001). There was little evidence for changes in 10 tested variables with increasing sonar SELsp, except reduced buzzing consistent with previously reported feeding cessation (t = −2.26, p = .02). A potential Lombard effect was detected during echolocation with sea state and SELsp, despite off-axis measurement and right-hand censoring due to acoustic clipping. The results are not conclusive on masking effects on sperm whale echolocation, highlighting challenges and opportunities for future anthropogenic masking studies

Sperm whales exhibit variation in echolocation tactics with depth and sea state but not naval sonar exposures

Funding: This work was supported by the UK Defense and Science Technology Laboratory (DSTLX-1000137649), NL Ministry of Defence (Cerema-DGA #1883003901), FR Ministry of Defence, and US Navy Living Marine Resources program (N39430-17-C-1935). PLT was supported by US Office of Naval Research (ONR) grant numbers N00014-18-1-2062 and N00014-20-1-2709, as well as by the Strategic Environmental Research and Development Program (SERDP) contracts RC20-1097, RC21-3091, and RC20-7188.Auditory masking by anthropogenic noise may impact marine mammals relying on sound for important life functions, including echolocation. Animals have evolved antimasking strategies, but they may not be completely effective or cost-free. We formulated seven a priori hypotheses on how odontocete echolocation behavior could indicate masking. We addressed six of them using data from 15 tagged sperm whales subject to experimental exposures of pulsed and continuous active sonar (PAS and CAS). Sea state, received single-pulse sound exposure level (SELsp), whale depth and orientation towards surface, and sonar were considered as candidate covariates representing different masking conditions. Echolocation behavior, including buzz duration and search range, varied strongly with depth. After controlling for depth and angle to the surface, the likelihood of buzzing following a click train decreased with sea state (t = −7.3, p < .001). There was little evidence for changes in 10 tested variables with increasing sonar SELsp, except reduced buzzing consistent with previously reported feeding cessation (t = −2.26, p = .02). A potential Lombard effect was detected during echolocation with sea state and SELsp, despite off-axis measurement and right-hand censoring due to acoustic clipping. The results are not conclusive on masking effects on sperm whale echolocation, highlighting challenges and opportunities for future anthropogenic masking studies.PostprintPostprintPeer reviewe

Large scale seabird community stucture along oceanographic gradients in the Scotia Sea and northern Antarctic Peninsula

Dataset and associated code for publication submitted to Frontiers in Marine Science. The data represent strip transect data collection efforts of seabirds aboard 2 tourist ships during the 2019-2020 Antarctic summer season throughout the Scotia Sea and Antarctic Peninsula. Data were analysed using R