Frequency tuning curves of the dolphin's hearing: envelope-following response study

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in dolphins (Turslops truncatus). The EFR was evoked by amplitude-modulated probes of various frequencies. A modulation rate of 600 Hz was found to fit the requirement to have a narrow spectrum and evoke EFR of large amplitude. Tuning curves were obtained within the frequency range from 11.2 to 110 kHz. The Q₁₀ values of the obtained tuning curves varied from 12–14 at the 11.2 kHz center frequency to 17–20 at the 64–90 kHz frequencies.Abbreviations ABR auditory brainstem response - EFR envelope following response - ERB equivalent rectangular bandwidth     

ABR frequency tuning curves in dolphins

Tone-tone masking was used to determine auditory brain-stem response tuning curves in dolphins (Tursiops truncatus) in a simultaneous-masking paradigm. The Q ₁₀ of the curves was as large as 16–19 in the frequency range 64–128 kHz. In the range 45–16 kHz, Q ₁₀ decreased proportionally to the frequency with the bandwidth of the curves being constant, about 3.5–4 kHz at the 10-dB level. Tuning curves below 45 kHz are supposed to reflect broad spectral bandwidth of the probe's effective part which is no longer than 0.5 ms, irrespective of actual probe duration. Tuning curves above 64 kHz are supposed to reflect the real frequency tuning of the dolphin's auditory system.Abbreviations ABR auditory brain stem response - AP action potential     

Anisakis simplex and Anisakis physeteris: physicochemical properties of larval and adult hemoglobins

To resolve the taxonomic relationship between two types of parasitic nematode larvae (Type I and II) and two species of parasitic nematode adults (Anisakis simplex and A. physeteris) of the aquatic ascarid genus Anisakis, collected in Japanese coastal water, a comparison was made of their hemoglobins' physicochemical properties. The larval hemoglobins were more similar to each other in electrophoretic pattern than to either adult, indeed there were few similarities whatsoever in these patterns of larval and adult hemoglobins. However, isoelectric points were 6.2 for the Type I larva and for A. simplex and 5.4 for the Type II larva and for A. physeteris. All samples showed identical patterns in spectrophotometric scanning. The circular dichroic spectra of the samples were also virtually identical, although slight differences were noted in the oxygenated hemoglobins; the Type II larva and A. physeteris exhibited a small positive peak at 575 nm but the Type I larva and A. simplex exhibited a much smaller peak (negative position). The sedimentation coefficients of the samples possessed essentially identical values (11.2–12.4). The molecular weights of the samples were estimated, roughly, to be in the range 33 to 43 × 10⁴ by thin-layer chromatography on Sephadex G-200. The evidence suggests that a relationship may exist between the Type I larva and A. simplex, and between the Type II larva and A. physeteris.     

CHANGES IN CLICK SOURCE LEVELS WITH DISTANCE TO TARGETS: STUDIES OF FREE-RANGING WHITE-BEAKED DOLPHINS LAGENORHYNCHUS ALBIROSTRIS AND CAPTIVE HARBOUR PORPOISES PHOCOENA PHOCOENA

ABSTRACT

Probably all odontocetes use echolocation for spatial orientation and detection of prey. We used a four hydrophone “Y” array to record the high frequency clicks from free-ranging White-beaked Dolphins Lagenorhynchus albirostris and captive Harbour Porpoises Phocoena phocoena. From the recordings we calculated distances to the animals and source levels of the clicks. The recordings from White-beaked Dolphins were made in Iceland and those from Harbour Porpoises at Fjord & Baelt, Kerteminde, Denmark during prey capture. We used stringent criteria to determine which clicks could be defined as being on the acoustic axis. Two dolphin and nine porpoise click series could be used to track individual animals, which presumably focused on the array hydrophones or a fish right in front of the array. The apparent source levels of clicks in the individual tracks increased with range. One individual White-beaked Dolphin and three Harbour Porpoises regulate their output signal level to nearly compensate for one-way transmission loss while approaching a target. The other dolphin regulated the output differently. For most of the recordings the sound level at the target remains nearly constant and the echo level at the animal increases as it closes on the target.     

The relative importance of reproduction and survival for the conservation of two dolphin populations

It has been proposed that in slow‐growing vertebrate populations survival generally has a greater influence on population growth than reproduction. Despite many studies cautioning against such generalizations for conservation, wildlife management for slow‐growing populations still often focuses on perturbing survival without careful evaluation as to whether those changes are likely or feasible. Here, we evaluate the relative importance of reproduction and survival for the conservation of two bottlenose dolphin (Tursiops cf aduncus) populations: a large, apparently stable population and a smaller one that is forecast to decline. We also assessed the feasibility and effectiveness of wildlife management objectives aimed at boosting either reproduction or survival. Consistent with other analytically based elasticity studies, survival had the greatest effect on population trajectories when altering vital rates by equal proportions. However, the findings of our alternative analytical approaches are in stark contrast to commonly used proportional sensitivity analyses and suggest that reproduction is considerably more important. We show that

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Connectivity in the network macrostructure of Tursiops truncatus in the Pelagos Sanctuary (NW Mediterranean Sea): does landscape matter?

The bottlenose dolphin (Tursiops truncatus Montagu, 1821) is a regularly observed species in the Mediterranean Sea, but its network organization has never been investigated on a large scale. We described the network macrostructure of the bottlenose dolphin (meta)population inhabiting the Pelagos Sanctuary (a wide protected area located in the north-western portion of the Mediterranean basin) and we analysed its connectivity in relation to the landscape traits. We pooled effort and sighting data collected by 13 different research institutions operating within the Pelagos Sanctuary from 1994 to 2011 to examine the distribution of bottlenose dolphins in the Pelagos study area and then we applied a social network analysis, investigating the association patterns of the photo-identified dolphins (806 individuals in 605 sightings). The bottlenose dolphin (meta)population inhabiting the Pelagos Sanctuary is clustered in discrete units whose borders coincide with habitat breakages. This complex structure seems to be shaped by the geo-morphological and ecological features of the landscape, through a mechanism of local specialization of the resident dolphins. Five distinct clusters were identified in the (meta)population and two of them were solid enough to be further investigated and compared. Significant differences were found in the network parameters, suggesting a different social organization of the clusters, possibly as a consequence of the different local specialization.     

Evidence for social role in a dolphin social network

Social animals have to take into consideration the behaviour of conspecifics when making decisions to go by their daily lives. These decisions affect their fitness and there is therefore an evolutionary pressure to try making the right choices. In many instances individuals will make their own choices and the behaviour of the group will be a democratic integration of everyone’s decision. However, in some instances it can be advantageous to follow the choice of a few individuals in the group if they have more information regarding the situation that has arisen. Here I provide early evidence that decisions about shifts in activity states in a population of bottlenose dolphin follow such a decision-making process. This unshared consensus is mediated by a non-vocal signal, which can be communicated globally within the dolphin school. These signals are emitted by individuals that tend to have more information about the behaviour of potential competitors because of their position in the social network. I hypothesise that this decision-making process emerged from the social structure of the population and the need to maintain mixed-sex schools.     

Stratification and intra- and inter-specific differences in fatty acid composition of common dolphin (Delphinus sp.) blubber: implications for dietary analysis

Sixty-five fatty acids were quantified in the blubber of common dolphins (Delphinus delphis, D. capensis) incidentally caught off the coast of southern California. Dolphins were grouped by sex, reproductive status and species, and a blubber sample was collected at a mid-lateral site located caudal to the trailing edge of the dorsal fin. Samples were divided horizontally into inner, middle and outer layers and gradients in fatty acid content (mass percent) were observed across the depth of the blubber. Levels of monounsaturated fatty acids were greatest in the outer layer, whereas levels of saturated and polyunsaturated fatty acids were greatest in the inner layer. Degree of stratification was greatest in sexually mature dolphins. Blubber of sexually immature, but physically mature, male dolphins was also highly stratified, suggesting that this difference may be attributed to differences in diet. Classification and regression tree analysis resulted in the fewest misclassifications when dolphins were grouped by species, possibly indicating that these closely related animals forage on different prey species. Dietary-derived fatty acids were typically selected as splitting criteria in classification and regression tree analyses, suggesting that the observed differences in fatty acid composition between the various groups of dolphins may be attributed to differences in diet.     

Localization of aquaporin-2, renal morphology and urine composition in the bottlenose dolphin and the Baird’s beaked whale

This study examined the distribution pattern of aquaporin-2 (AQP2), relative medullary thickness (RMT) and urine properties in the bottlenose dolphin Tursiops truncatus and Baird’s beaked whale Berardius bairdii. Immunohistochemical studies revealed that AQP2 was localized in the collecting tubules/ducts of both species’ renicules, as in terrestrial mammals. The collecting ducts with AQP2 were thinner and arranged more densely in the dolphin than in the whale. RMT values in the renicule were moderate in both species, but were significantly higher in the dolphin (6.0 ± 0.9) than the whale (4.9 ± 0.7). Urine of the bottlenose dolphin is comparatively concentrated (osmolality: 1715.7 ± 279.4 mOsm kg⁻¹, Na⁺: 490.1 ± 87.9 mmol l⁻¹, Cl⁻: 402.7 ± 79.6 mmol l⁻¹, K⁺: 80.7 ± 25.8 mmol l⁻¹, urea nitrogen: 703.5 ± 253.9 mmol l⁻¹), while urine of the dead Baird’s beaked whale is less concentrated (osmolality: 837.5 ± 293.8 mOsm kg⁻¹, Na⁺: 192.9 ± 81.5 mmol l⁻¹, Cl⁻: 159.9 ± 71.4 mmol l⁻¹, K⁺: 44.3 ± 29.5 mmol l⁻¹, urea nitrogen: 270.7 ± 120.3 mmol l⁻¹). These data suggest it is possible that the differences in these renal morphological features may be related in some way to the difference in urine composition between the species, although further studies are necessary. M. Suzuki and N. Endo are equal contributors to this study.     

Spatio-temporal analysis of cetacean strandings and bycatch in a UK fisheries hotspot

Marine vertebrate strandings data can provide insights into the long-term dynamics of cetacean populations, and the threats they face. We investigate whether the spatio-temporal patterns of cetacean strandings around Cornwall, SW Britain, have changed in the past century. Analysis of strandings from 1911 to 2006 (n = 2,257) show that, since the mid-1970s, the relative frequency of strandings of common dolphins (Delphinus delphis), harbour porpoises (Phocoena phocoena) and pilot whales (Globicephala melas) has increased significantly. Seasonal peaks in strandings frequencies are apparent, between December and March for harbour porpoises and common dolphins, and between November and January for pilot whales. There were significant positive trends in the number of common dolphin and harbour porpoise strandings, as a proportion of total strandings, over time. Strandings of common dolphins, porpoises and all other species occur more frequently on the south coast of Cornwall. A total of 415 cetaceans were subject to full veterinary necropsy to determine cause of death, between 1990 and 2006, and 253 (61%) of these individuals were determined to have died due to bycatch in fishing gear. Analyses of industrialised fishing pressure in UK waters show the seas around Cornwall to be one of the most heavily fished areas of the UK. We suggest a number of factors that could be responsible for the recent increases in cetacean strandings in southwest UK waters in recent years, including survey effort, as well as abundance and range shifts that are potentially linked with climate change. Although detectable levels of bycatch rate have not increased over time, fisheries interactions are in significant part responsible for mortality patterns and are worthy of more detailed investigation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.