The acoustic behaviour of resident bottlenose dolphins in Fiordland, New Zealand

The bottlenose dolphin Tursiops truncatus is an extremely well-studied species. We have an extensive knowledge of certain aspects of their vocal behaviour, particularly from captive contexts. Bottlenose dolphins produce a rich tapestry of vocalisations, however, which have historically received minimal attention. Resident groups of bottlenose dolphins frequent the waterways of Fiordland in southwest New Zealand. These deep, sheltered fiords are ideally suited for acoustic studies. This thesis presents the first detailed study of bottlenose dolphin acoustics in New Zealand. Both narrowband and broadband systems were used to record the vocalisations of two resident groups. Effort was distributed evenly over three years for both Doubtful Sound and Milford Sound. From 875 recordings, I proposed a repertoire of 15 discrete calls. These categories were subsequently compared using parameters measured from almost 2000 individual vocalisations. Various multivariate techniques revealed some redundancy in the proposed repertoire, and it was subsequently reduced to 12 calls. The 12 call repertoire was compared between the potentially interbreeding populations of Doubtful Sound and Milford Sound. Fiord-specificity was revealed for many of the calls, particularly the sequenced calls and whistles. These differences suggest bottlenose dolphins use dialects, in keeping with studies of killer whales and sperm whales. As Fiordland dolphins are out of sight for 90% of the time, acoustic techniques allow inference in to subsurface behaviour. I investigated sequential relationships among sounds and between sounds and behaviours. Many calls were strongly implicated in social interactions. The vocalisations ratchet, orca and the sequenced calls were associated with periods of conflict. A number of the click-based calls were linked to diving and presumed foraging events. Inference on the functional significance of sounds allowed an interpretation of habitat use. This appears to be the first study relating the entire vocal repertoire of a cetacean population to a complete home range. Areas important for socialising, foraging and resting are proposed. Local management decisions may be well served by this information. This study uses benign techniques to build on previous research in Fiordland, and adds a new dimension to the study of these populations

Observações de cetáceos por iatistas no Atlântico Norte : um estudo piloto.

In the summer of 1998, yachtsmen sailing from the Caribbean to the Azores were encouraged to take part in an Atlantic cetacean survey. The principle aim of this project was to evaluate the potential of using regular seafarers as sources of data on cetacean distribution. Identification guides and sighting forms were distributed and participants were asked to record any cetacean sightings as well as to conduct routine set-effort watches. A secondary aim of the project was to investigate reports of illegal whaling in the Atlantic. Data collected from the yachtsmen reveal a concentration of sightings along the mid- Atlantic ridge, perhaps corresponding to an increase in productivity in this area. No further reports of whaling activity were made. Although this work only involves a small data set, it illustrates how useful yachtsmen can be in assisting research in otherwise inaccessible regions. Future involvement of yachtsmen in cetacean surveying should be encouraged, as long-term data sets gathered in this way can be invaluable in revealing offshore trends

Acoustic estimates of sperm whale abundance in the Mediterranean Sea as part of the ACCOBAMS Survey Initiative

Acoustic surveys for sperm whales (Physeter macrocephalus) were conducted in the Mediterranean Sea in summer 2018 as part of the vessel-based component of the ACCOBAMS Survey Initiative (ASI). Equal-spaced zigzag transects provided uniform coverage of key sperm whale habitats and were surveyed using a towed hydrophone array deployed from a research vessel at speeds of 5-8 knots. A total of 14,039 km of tracklines were surveyed in the western basin, Hellenic Trench and Libyan waters, with an acoustic coverage of 10% realised for sperm whales. During these surveys, 254 individual sperm whales were detected on the trackline, with an additional 66 individuals off-track. Sperm whales were only seen ten times on-track, with an additional 16 off-track sightings. Estimates of slant range to echolocating whales were used to derive density estimates through both design- and model-based distance sampling methodologies. An acoustic availability of 0.912 (sd = 0.036) was derived from via published models. When correcting for availability bias, a design-based abundance estimates of 2,673 individuals (95% CI 1,739-4,105; CV = 0.21) was derived for the surveyed blocks, which incorporated most known sperm whale habitat in the Mediterranean Sea. The equivalent model-based estimate was 2,825 whales (2,053-3,888; CV = 0.16). Over 97% of detected whales were in the western basin, with highest densities in the Algerian and Liguro-Provencal Basins between Algeria and Spain/France. In the eastern basin, detections were sparse and concentrated along the Hellenic Trench. A density surface modelling (DSM) exercise identified location and benthic aspect as being the most instructive covariates for predicting whale abundance. Distance sampling results were used in a power analysis to quantify the survey effort required to identify population trends. In the most extreme scenario modelled (10% per annum decline with decennial surveys), the population could have dropped by 90% before the decline was identified with high statistical power. Increasing the regularity of surveys would allow population trends to be detected more expediently. Mediterranean sperm whales are listed as Endangered on the IUCN’s Red List and the need for urgent conservation measures to reduce injury and mortality remains paramount for this unique sub-population

Temporal patterns in dolphin foraging activity in the Mediterranean Sea: insights from vocalisations recorded during the ACCOBAMS Survey Initiative

Marine organisms continually adapt their physiology and behaviour to temporal variations in their environment, resulting in diurnal rhythmic behaviour, particularly when foraging. In delphinids, these rhythms can be studied by recording echolocation clicks, which can provide indicators of foraging activity. The foraging rhythms of delphinids and their relationship to temporal parameters are poorly documented and most studies so far have used moored passive acoustic systems. The present study provides, for the first time, information on the activity rhythms of delphinids investigated in relation with temporal variables at a basin scale from a moving platform, in the western and central Mediterranean Sea. We used passive acoustic recordings collected by hydrophones towed along transect lines during the ACCOBAMS Survey Initiative in the summer 2018. We extracted variables that may influence daily and monthly rhythms, including time of day, lunar cycle, lunar illumination and sea state and fitted generalised additive models. The nycthemeral and lunar cycles were the two main factors influencing dolphin activity rhythms. Echolocation activity was predominant at night, with a maximum of 0.026 acoustic events per minute at 21:00/22:00 compared to as few as 0.0007 events per minute at 11:00. These events were also more frequent during the third quarter of the moon; 0.033 acoustic events on day 22 of the lunar cycle as opposed to 0.0008 on day 8 of the lunar cycle, corresponding to the first quarter of the moon. Variations in the echolocation activity of delphinids in the Mediterranean Sea could reflect variation in their foraging effort and be related to prey density, composition, accessibility and catchability within dolphin foraging depth range. These results should also improve interpretation of passive acoustic monitoring data

Large‐scale modelling of deep‐diving cetacean habitats

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The acoustic behaviour of resident bottlenose dolphins in Fiordland, New Zealand

The bottlenose dolphin Tursiops truncatus is an extremely well-studied species. We have an extensive knowledge of certain aspects of their vocal behaviour, particularly from captive contexts. Bottlenose dolphins produce a rich tapestry of vocalisations, however, which have historically received minimal attention. Resident groups of bottlenose dolphins frequent the waterways of Fiordland in southwest New Zealand. These deep, sheltered fiords are ideally suited for acoustic studies. This thesis presents the first detailed study of bottlenose dolphin acoustics in New Zealand. Both narrowband and broadband systems were used to record the vocalisations of two resident groups. Effort was distributed evenly over three years for both Doubtful Sound and Milford Sound. From 875 recordings, I proposed a repertoire of 15 discrete calls. These categories were subsequently compared using parameters measured from almost 2000 individual vocalisations. Various multivariate techniques revealed some redundancy in the proposed repertoire, and it was subsequently reduced to 12 calls. The 12 call repertoire was compared between the potentially interbreeding populations of Doubtful Sound and Milford Sound. Fiord-specificity was revealed for many of the calls, particularly the sequenced calls and whistles. These differences suggest bottlenose dolphins use dialects, in keeping with studies of killer whales and sperm whales. As Fiordland dolphins are out of sight for 90% of the time, acoustic techniques allow inference in to subsurface behaviour. I investigated sequential relationships among sounds and between sounds and behaviours. Many calls were strongly implicated in social interactions. The vocalisations ratchet, orca and the sequenced calls were associated with periods of conflict. A number of the click-based calls were linked to diving and presumed foraging events. Inference on the functional significance of sounds allowed an interpretation of habitat use. This appears to be the first study relating the entire vocal repertoire of a cetacean population to a complete home range. Areas important for socialising, foraging and resting are proposed. Local management decisions may be well served by this information. This study uses benign techniques to build on previous research in Fiordland, and adds a new dimension to the study of these populations

Encounter rates of cetaceans in the Mediterranean Sea and contiguous Atlantic area

A series of visual-acoustic surveys were carried out in the Mediterranean Sea between 2003 and 2007 from RV 'Song of the Whale'. Almost 21,000 km of trackline were surveyed between the longitudes of 14 degrees W and 36 degrees E with an emphasis on regions with low survey effort. Survey tracklines were designed to provide even coverage probability with random start points. Ten cetacean species were positively identified (sperm whale, fin whale, Cuvier's beaked whale, false killer whale, long-finned pilot whale, Risso's dolphin, common bottlenose dolphin, rough-toothed dolphin, striped dolphin and short-beaked common dolphin). Several of these species, plus sei whale and harbour porpoise, were also encountered in the Atlantic contiguous area (the entrance waters of the Mediterranean between the Iberian Peninsula and north-west Morocco). These surveys expand and clarify the known distributions of cetaceans within the Mediterranean basin. New species documented from Libyan waters include sperm whale, striped dolphin and rough-toothed dolphin. False killer whales and rough-toothed dolphins were documented for the first time off Cyprus. Live harbour porpoises were seen for the first time on Morocco's Atlantic seaboard. It is suggested that the status of rough-toothed dolphins in the Mediterranean be revised from visitor to regular species. Substantial new information on encounter rates is now available for the planning of a basin-wide systematic survey of cetaceans within the Mediterranean Sea and contiguous Atlantic waters.</p