Small Delphinids Research Articles

Pharmaceutical residues in stranded dolphins in the Bay of Biscay

There is a growing concern about the presence of pharmaceuticals on the aquatic environment, while the marine environment has been much less investigated than in freshwater. Marine mammals are suitable sentinel species of the marine environment because they often feed at high trophic levels, have unique fat stores and long lifespan. Some small delphinids in particular serve as excellent sentinel species for contamination in the marine environment worldwide. To the best of our knowledge, no pharmaceuticals have been detected or reported in dolphins so far.In the present study, muscle, liver and blubber samples from three common dolphins (Delphinus delphis) and seven striped dolphins (Stenella coeruleoalba) stranded along the Basque Coast (northern Spain) were collected. A total of 95 pharmaceuticals based on detectability and predicted ability to bioaccumulate in fish were included in the liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis.At least one pharmaceutical was found in 70 % of the individuals. Only three of the 95 monitored pharmaceuticals were detected in dolphin's tissues. Very low concentrations (<1 ng/g) of orphenadrine and pizotifen were found in liver and promethazine in blubber.Herein, the gap in the knowledge regarding the study organisms and marine environments with respect to pharmaceutical pollution, which demands further research to understand if pharmaceuticals are a threat for these apex predators, is highlighted and discussed.

Pathology of short-term dorsal fin tag-attachments in tagged and re-stranded short-beaked common dolphins Delphinus delphis on Cape Cod, MA

Odontocetes are difficult to study in the wild, making tagging and remote tracking a valuable practice. However, evaluations of host responses at tagging sites have been primarily limited to visual observations in the field. Here we explore the macro- and microscopic pathology of dorsal fin tag attachments in 13 stranded and released short-beaked common dolphins Delphinus delphis from Cape Cod, MA that later re-stranded and died or were euthanized 1-28 d post-tagging. Tags were attached to stranded dolphins’ dorsal fins using 2 methods: core biopsy or piercing. Grossly, the piercing method resulted in epidermal compression into the dermis. One tag site had a necrotic border 28 d after application. Grossly, the biopsy method resulted in minimal to no tissue reaction. Two tag sites had granulation tissue accumulation 4 and 12 d after tagging. Histopathologic findings for all tag types and animals consisted of focal epithelial loss, dermal edema, perivascular edema, inflammation and hyperplasia, and inter- and extracellular edema in the adjacent epidermis. Minor expected pathological changes given the procedure were also observed: superficial epidermal necrosis in 3 cases, and superficial bacterial colonization in 2 cases. There was no evidence of sepsis and tagging was not related to cause of re-stranding or death in any case. These gross and histopathologic findings support previous observational conclusions in small delphinids that with appropriate sterile technique, the impacts of single pin dorsal fin tagging on the animal can be minimal and localized. Of the 2 methods, core biopsy may be a better tagging method.

In the Wrong Place at the Wrong Time: Identifying Spatiotemporal Co-occurrence of Bycaught Common Dolphins and Fisheries in the Bay of Biscay (NE Atlantic) From 2010 to 2019

The first Unusual Mortality Event (UME) related to fishing activity along the Atlantic coast recorded by the French Stranding Network was in 1989: 697 small delphinids, mostly common dolphins, washed ashore, most of them with evidence of having been bycaught. Since then, UMEs of common dolphins have been observed nearly every year in the Bay of Biscay; unprecedented records were broken every year since 2016. The low and unequally distributed observation efforts aboard fishing vessels in the Bay of Biscay, as well as the lack of data on foreign fisheries necessitated the use of complementary data (such as stranding data) to elucidate the involvement of fisheries in dolphin bycatch. The aim of this work was to identify positive spatial and temporal correlations between the likely origins of bycaught stranded common dolphins (estimated from a mechanistic drift model) and fishing effort statistics inferred from Vessel Monitoring System (VMS) data on vessels &amp;gt;12 m long. Fisheries whose effort correlated positively with dolphin mortality areas after 2016 included French midwater trawlers, French Danish seiners, French gillnetters, French trammel netters, Spanish bottom trawlers, and Spanish gillnetters. For the French fleet only, logbook declarations, sales, and surveys carried out by Ifremer were integrated into fishing effort data. Six fleets were active in common dolphin bycatch areas at least twice between 2016 and 2019: gillnetters fishing hake, trammel netters fishing anglerfish, bottom pair trawlers fishing hake, midwater pair trawlers fishing sea bass and hake, and Danish seiners fishing whiting. Except for changes in hake landings in some fisheries, there were no notable changes in total fishing effort practice (gear or target species) based on the data required by the ICES and Council of the European Union that could explain the large increase in stranded common dolphins recorded along the French Atlantic coast after 2016. Small scale or unrecorded changes could have modified interactions between common dolphins and fisheries, but could not be detected through mandatory data-calls. The recent increase in strandings of bycaught common dolphins could have been caused by changes in their distribution and/or ecology, or changes in fishery practices that were undetectable through available data.

New evidences about small delphinids stranding in the west Algerian coast

The Cetaceans are marine mammals that often get stranded along the Algeri-an coast, due to several factors (parasitism, marine pollution, injuries, acci-dental fishing, etc.). In view of the growing interest in the knowledge of ma-rine mammals stranding, an effort to collect this information in the west Al-gerian coast has been carried out by the Environmental Monitoring Network Laboratory since 80s. The aim of this study is to describe and provide new evidences about the stranding of the small delphinids in the Algerian west-ern coast. The study was conducted on 35 individuals of small delphinids reported stranded and dead on-shore from three districts (Mostaganem, Oran and AinTemouchent). Five different specieshave been identified, in-cluding three frequent common species (D. delphis, S. coeruleoalba, T.truncatus) along with two relatively less frequent species (G. melas, G.griseus). Life history information was gathered in terms of morphometrics and sex. The stranded individuals were small to medium-sized cetaceans, ranging from about 0.6 meter to almost 5 meter in length, with an average languor of 2.25 ±1.01 meter. Aside from undetermined individuals due to advanced decomposition of the carcass, the sex ratio of male vis a vis of fe-male was of 0.78 clearly indicating a female predominance. An assessment of causes of mortality was conducted using different observing indexes. It turns out that the most likely cause of the mortality is attributed to inci-dental human actions by entanglement in fishing gear and ships collisions with small delphinids are a conservation problem of growing concern world-wide. This study improves knowledge on small delphinids stranding through the west Algerian coast and has broad implications in establishing a conser-vation management program.

Kinship influences social bonds among male southern Australian bottlenose dolphins (Tursiops cf. australis)

Male mammals employ a wide variety of mating strategies in order to increase their reproductive success, which in turn influence their social behavior. In some populations of bottlenose dolphins (Tursiops spp.), males cooperate in small groups or alliances to gain access to females for mating. However, the occurrence of these male cooperative groups has been predicted to occur only under certain social and ecological conditions, driven by factors such as differences in population density, operational sex ratio, and sexual size dimorphism. Here, we used generalized affiliation indices, social network techniques, and maternally and bi-parentally inherited genetic markers to investigate the affiliation patterns and genetic relatedness among male southern Australian bottlenose dolphins (Tursiops cf. australis) in a small embayment in South Australia. Photo-identification data and biopsy samples were collected in Coffin Bay from 2013 to 2015 through systematic boat-based surveys. We found that highly sighted male dolphins formed 12 social clusters composed of two to five individuals. Genetic analyses revealed that general male affiliation patterns were significantly correlated with mtDNA haplotype sharing. In addition, preferred affiliates showed significantly higher levels of genetic relatedness compared to casual and avoided male pairs. Our results corroborate theoretical expectations for the formation of social bonds in small delphinids and suggest that a high density of dolphins, with an expected skewed operational sex ratio and no apparent sexual size dimorphism, is likely to have favored the formation of strong male affiliations. In addition, the availability of genetic relatives within the population may have favored male affiliations based on kinship relationships. Male bottlenose dolphins use different strategies to gain access to females, from single roving individuals, pairs or trios in alliances, to stable mixed-sex groups. Moreover, the role of kinship in the formation of male social bonds also varies within and among populations. This variability has been attributed to differences in ecological and intrinsic factors. Here, we studied the affiliation patterns and genetic relatedness in southern Australian bottlenose dolphins and demonstrated that kinship plays an important role in the formation of close male social ties. Furthermore, the results corroborate previous findings about the factors that contribute to the formation of male social bonds in these animals.

Comparison of habitat models for scarcely detected species

When performing habitat models, modellers have to choose between presence-absence and presence-only models to estimate the habitat preferences of a species. Primarily, this choice depends on the data that are available and whether effort data are recorded in parallel to sighting data. For species that are rare or scarce, the models have to address a great number of zeros (i.e., no animal seen) that weakens the ability to make sound ecological inferences. We tested two types of habitat models (presence-absence vs. presence-only) to determine which type best dealt with datasets containing an excess of zeros, and we applied our models to a sighting dataset that included the common (Delphinus delphis) and striped (Stenella coeruleoalba) dolphin (approximately 92% zeros). We used two types of presence-absence models (Generalised Additive models – GAMs, Generalised Linear Model – GLM) and one presence-only model, a MaxEnt model, and we used various criteria to compare these models (i.e., AIC, deviances, rootograms and distribution patterns predicted by the models). Overall, we observed that the presence-absence models made better predictions than the presence-only model. Among the presence-absence models, the GAM with a Negative Binomial distribution was better at predicting small delphinids habitats, even though the GAM with a Tweedie distribution exhibited similar results. However, the zero-inflated Poisson distributions exhibited less convincing results and was contrary to what was expected. Finally, despite 92% zeros, our dataset was not zero-inflated. Our study demonstrates the importance of selecting appropriate models to make reliable predictions of habitat use for species that are rare or scarce.

Seasonal distribution and abundance of cetaceans within French waters- Part I: The North-Western Mediterranean, including the Pelagos sanctuary

The biodiversity of the Mediterranean Sea is undergoing important changes. Cetaceans, as top predators, are an important component of marine ecosystems. The seasonal distribution and abundance of several cetacean species were studied with a large aerial survey over the North-Western Mediterranean Sea, including the international Pelagos sanctuary, the largest Marine Protected Area (MPA) designed for marine mammals in the Mediterranean. A total of 8 distinct species of cetaceans were identified, and their occurrence within the sanctuary was investigated. Abundance estimates were obtained for three groups of species: the small delphinids (striped dolphins mainly), the bottlenose dolphin and the fin whale. There was a seasonal variation in striped dolphin abundance between winter (57,300 individuals, 95% CI: 34,500–102,000) and summer (130,000, 95% CI: 76,800–222,100). In contrast, bottlenose dolphin winter abundance was thrice that of summer. It was also the only species to exhibit any preference for the Pelagos sanctuary. Fin whale abundance had the reverse pattern with winter abundance (1000 individuals, 95% CI: 500–2500) and summer (2500 individuals, 95% CI: 1500–4300), without any preference for the sanctuary. Risso's dolphins, pilot whales and sperm whales did not exhibit strong seasonal pattern in their abundance. These results provide baseline estimates which can be used to inform conservation policies and instruments such as the Habitats Directive or the recent European Marine Strategy Framework Directive.

Diversity and Distribution Patterns of Cetaceans in the Subtropical Southwestern Atlantic Outer Continental Shelf and Slope

Temporal and spatial patterns of cetacean diversity and distribution were investigated through eight ship-based surveys carried out during spring and autumn between 2009 and 2014 on the outer continental shelf (~150m) and slope (1500m) off southeastern and southern Brazil (~23°S to ~34°S). The survey area was divided into southeast and south areas according to their oceanographic characteristics. Twenty-one species were observed in 503 sightings. The overall number of species was similar between the two areas, though it was higher in the spring in the south area. Five species were dominant and diversity varied more seasonally than spatially. ANOVA and kernel analyses showed that overall cetacean densities were higher in spring compared to autumn. Physeter macrocephalus, the most frequent species, concentrated throughout the south area at depths over 1000m in both seasons. Despite the overlapped occurrence at a broader scale, small delphinids presented latitudinal and in-offshore gradients as well as seasonal variation in distribution patterns, which could indicate habitat partitioning between some species. Delphinus delphis was only recorded in the south and its density decreased in areas where the presence of Stenella frontalis increased, mainly beyond the 250m isobath. Densities of S. longirostris and S. attenuata increased in lower latitudes and beyond the shelf break. The large delphinids Tursiops truncatus and Globicephala melas formed mixed groups in many occasions and were observed along the study area around depths of 500m. Grampus griseus was twice as frequent in the south area and densities increased in waters deeper than 600m. As expected, densities of both small and large migratory whales were higher during spring, over the continental slope, in the southeast area. The results presented here provided strong evidence on the importance of the outer continental shelf and slope to a diverse community of cetaceans occurring in the subtropical Southwestern Atlantic.

Five Decades of Marine Megafauna Surveys from Micronesia

Long-term data are critical for assessing the status, trends, abundance, and distributions of wildlife populations. However, such data streams are often lacking for protected species, especially highly mobile marine vertebrates. Using five decades of aerial surveys, we assessed changes in marine megafauna on the insular coral reef ecosystem of Guam (Marianas Archipelago in Micronesia). The data allowed estimates of relative abundance, trends, and geographic distributions for several important taxa: sea turtles, sharks, manta rays, small delphinids, and large delphinids. These surveys occurred in 32 years from 1963-2012 amounting to 632 flights lasting 809 hours over a 70.16 km2 area. Over this span, surveyors recorded 10,622 turtle, 1,026 shark, 60 manta ray, 7,515 small delphinid, and 95 large delphinid observations. Since the 1960s, sea turtles increased an order of magnitude (r = 0.07) and sharks decreased five-fold (r = -0.03). Turtle increases were largely restricted to one geographical area, where optimal habitat coincides with low human density and a marine protected area. Shark observations declined proximate to human population centers. Trends for the other taxa were less informative, but each taxon had geographic foci. Protections in the region may be working to recover turtle populations, but failing (or have not yet had sufficient time) to recover overfished shark populations. Long-term analyses of vulnerable marine megafauna in this data-limited region are uncommon, and should be used to guide more focused studies that inform regional management and conservation of these species.

How much are stranding records affected by variation in reporting rates? A case study of small delphinids in the Bay of Biscay

Marine vertebrate strandings offer an opportunistic sampling scheme that can provide abundant data over long periods. Because the stranding process involves biological, physical and sociological parameters, confounding complicates the interpretation of results. The statistical analysis of these data relies on generalized linear or additive models in order to infer long-term trends, but does not easily account for drift or variation in reporting rates. Here, we capitalized on county-level (administrative) variation following the passing of a law for compulsory reporting of stranded marine mammals in France to investigate how variation in reporting rates may affect the observed trend in stranded small delphinids in the Bay of Biscay. Using a time-series spanning more than 30 years across eight administrative counties, we built variance partitioning models for the analysis of count data. We discussed the choice of an appropriate likelihood to conclude the Negative Binomial useful and interpretable in the context of small delphinid strandings. We expanded the model with a recent methodology to detect structural breaks in the time series, focusing on overdispersion. We performed statistical robustness checks with respect to variations in reporting rates and discuss their causal interpretation in the context of observational data. Stranding frequencies increased on average 7-fold over 30 years. We conclude that reporting rates to the French stranding network have been stable since the early 1990s, and the average 3-fold increase in stranded small delphinids observed in the Bay of Biscay since 1990 is due to other factors, including bycatch. Codes and data are available to replicate the analysis to other national stranding networks.

Long‐term social structure of a resident community of Atlantic spotted dolphins, Stenella Frontalis, in the Bahamas 1991–2002

AbstractLong‐term social structure data on small delphinids is lacking for most species except the bottlenose dolphin. This study describes the long‐term social structure of one community of Atlantic spotted dolphins, Stenella frontalis, divided into three social clusters. Data from 12 yr were analyzed using SOCPROG 2.3. Coefficients of association (CoA) were calculated using the half‐weight index. The overall mean community CoA ranged from 0.09 to 0.12. Temporal analyses and mantel tests revealed significant differences between sex class associations due to high male‐male CoA (0.12–0.23) compared to female‐female and mixed sex CoA (0.08–0.10). Female associations were strongly influenced by reproductive status, calf care, and social familiarity, but not by age class. Male associations were strongly influenced by age, access to females, and alliance formation. Males showed two levels of alliance formation, long‐term first order pairs/trios (CoA 0.70–1.00) and shorter‐term second order alliances between two or more first order alliances (CoA 0.45–0.69), and a possible third level during interspecies interactions. Mating strategies, sex, and cluster formation shaped the social structure in this spotted dolphin community. Similar to many bottlenose dolphin studies, long‐term affiliations for spotted dolphins were correlated with age, sex, and reproductive status.

Are there biases in biopsy sampling? Potential drivers of sex ratio in projectile biopsy samples from two small delphinids

AbstractMolecular assays were used to determine the sex of 1,294 biopsied common dolphins (658 long‐beaked common dolphins,Delphinus capensis, and 636 short‐beaked common dolphins,D. delphis) in the Southern California Bight. Sex ratio differed substantially between the two species; females comprised 241 (36.6%) ofD. capensissamples and 410 (64.5%) ofD. delphissamples. All biopsies were taken either from a large research ship or from a small, rigid‐hull inflatable boat (RHIB) launched from the larger ship. When conducting replicate biopsy effort on the same schools from each vessel/platform (“Tandem Biopsy Sampling”), we found evidence that disproportionately more femaleD. capensiswere biopsied from theRHIBthan from the ship but the same was not true forD. delphis. We suspect that these results are driven by bowriding‐behavior differences between the two species. Biopsy duration, geographic location, school size, and Julian date were considered as potential covariates with sex ratio; geographic location was the only one to show strong evidence of correlation. This study also presents an alternative to the erroneous practice of comparing sex ratios to a theoretical assumption of parity (i.e., 50:50 sex ratio) when researchers avoid sampling animals paired with calves.

Megavertebrate communities from two contrasting ecosystems in the western tropical Atlantic

Productivity was shown to structure megavertebrate communities, particularly in tropical oceans where they may be under selective pressure to maintain their foraging success in these low productivity environments. However, overall oligotrophic tropical oceans may encompass contrasting ecosystems. In the western tropical Atlantic, the Antilles and Guiana belong to two different biogeographic provinces and surface chlorophyll concentration is on average 10 times higher in Guiana. The aim of this study was to document megavertebrate communities in terms of encounter rates, species composition, abundance and spatial distribution and to compare them between these two contrasting regions. As part of an aerial census of cetaceans and other megavertebrates, line transect surveys were conducted across the French Antilles and Guiana. Both distance sampling and geostatistics were used to estimate abundance and geostatistics also provided maps of local density. Cetacean encounter rate was 3 times higher in Guiana (1.8sightings/100km) compared to the Antilles (0.6sightings/100km). Moreover, small delphinids strongly dominated in Guiana (representing 83% of the odontocete sightings) with a high abundance of bottlenose dolphins (Tursiops truncatus) (34,965 individuals, CV=0.28). Seabird encounter rate was similar in both regions (4.7sightings/100km in the Antilles and 3.6sightings/100km in Guiana). Charadriiformes, mainly represented by terns, were abundant in both regions whereas Pelecaniformes were only abundant in the Antilles and represented by frigatebirds, tropicbirds and boobies. Additionally, cetaceans and seabirds were mainly distributed close to the islands in the Antilles and were more widely distributed in Guiana. This study provided new information about megavertebrates which are poorly documented in these waters and highlighted differences in communities between these contrasting ecosystems. In particular, odontocete communities appeared to respond to productivity and may be structured by a differential distribution of resources through the water column.

Sociogenetic structure, kin associations and bonding in delphinids

Social systems are the outcomes of natural and sexual selection on individuals' efforts to maximize reproductive success. Ecological conditions, life history, demography traits and social aspects have been recognized as important factors shaping social systems. Delphinids show a wide range of social structures and large variation in life history traits and inhabit several aquatic environments. They are therefore an excellent group in which to investigate the interplay of ecological and intrinsic factors on the evolution of mammalian social systems in these environments. Here I synthetize results from genetic studies on dispersal patterns, genetic relatedness, kin associations and mating patterns and combine with ecological, life history and phylogenetic data to predict the formation of kin associations and bonding in these animals. I show that environment type impacts upon dispersal tendencies, with small delphinids generally exhibiting female-biased philopatry in inshore waters and bisexual dispersal in coastal and pelagic waters. When female philopatry occurs, they develop moderate social bonds with related females. Male bonding occurs in species with small male-biased sexual size dimorphism and male-biased operational sex ratio, and it is independent of dispersal tendencies. By contrast, large delphinids, which live in coastal and pelagic waters, show bisexual philopatry and live in matrilineal societies. I propose that sexual conflict favoured the formation of these stable societies and in turn facilitated the development of kin-biased behaviours. Studies on populations of the same species inhabiting disparate environments, and of less related species living in similar habitats, would contribute towards a comprehensive framework for the evolution of delphinid social systems.

Steno bredanensis (Cetacea: Delphinidae)

Steno bredanensis (Cuvier in Lesson, 1828) is a small odontocete commonly called the rough-toothed dolphin. A slender, gray dolphin with a slightly darker cape, this species is most easily distinguished from other small delphinids by a gradually sloping forehead and a long rostrum. It is the only species in the genus Steno. Despite reports of sightings or stranded specimens from all tropical and subtropical oceans, the species is thought to typically occur in low abundance. The conservation status of S. bredanensis is poorly known.

Insights From Whaling Logbooks on Whales, Dolphins, and Whaling in the Gulf of Mexico

Whaling voyage logbooks provide a unique window into historical marine animal distribution and relative numbers. The Gulf of Mexico was among the regions visited by American commercial whalers beginning in the late 1700s, and possibly as early as the 1760s. For more than a century, they hunted sperm whales (Physeter macrocephalus) and blackfish (usually probably short-finned pilot whales; Globicephala macrorhynchus) in the Gulf. An ongoing study of global whaling history has allowed us to offer some insights on characteristics and trends of the Gulf fishery and on cetacean populations in the Gulf. We examined 53 voyage logbooks that included some whaling in the Gulf. Using the information from those logbooks and other sources, we identified 204 different voyages that included one or more ‘‘vessel-seasons’’ of whaling in the Gulf (total of 214 vessel-seasons) between 1788 and 1877. More than three-quarters (76%) of the 186 voyages for which the rig type is known were by brigs or schooners; they sailed primarily from the Massachusetts ports of New Bedford and Nantucket initially and Provincetown in later years. The whaling took place mainly in deep portions of the Gulf and in the first 7 mo of the calendar year (i.e., from Jan. through July). The sperm whales hunted in the Gulf tended to be small and were usually taken from schools, suggesting that they were mostly juveniles and females. Observations (and occasionally catches) of other cetaceans besides sperm whales and blackfish are mentioned in the logbooks—mainly ‘‘finbacks’’ (Balaenoptera sp.), killer whales (Orcinus orca), and ‘‘porpoises’’ (various small delphinids).

Structure of a toothed cetacean community around a tropical island (Mayotte, Mozambique Channel)

We describe the structure of a toothed cetacean community around the island of Mayotte (South-West Indian Ocean, 45°10′ E, 12°50′ S), using data collected from small boat-based surveys conducted between July 2004 and June 2006. In all, 16 odontocete species were recorded. Diversity (Shannon-Weaver index) was particularly high along the outer slope of the barrier reef. Patterns of spatial distribution underscore the existence of three main cetacean habitat types: the inner lagoon (Indo-Pacific bottlenosed dolphin Tursiops aduncus and humpback dolphin Sousa chinensis), the outer-reef slope (spinner dolphin Stenella longirostris, pantropical spotted dolphin S. attenuate and melon-headed whale Peponocephala electra) and oceanic waters deeper than 500 m (e.g. Blainville's beaked whale Mesoplodon densirostris). Group characteristics were highly variable among species, with oceanic small delphinids characterised by larger group sizes than strictly coastal and non-delphinid oceanic species. The outer slope of the barrier reef appears to be of primary importance in terms of density and diversity of odontocetes around Mayotte. Results support the hypothesis that a number of cetacean species, particularly several delphinid species, are dependent on coral reef complexes.

Individual and group behavioural reactions of small delphinids to remote biopsy sampling

AbstractBiopsy sampling is an effective technique for collecting cetacean skin and blubber samples for various biological studies. However, determining the impact of this research practice is important, as it may vary between sites, species and equipment used. We examined the short-term behavioural reactions of four small (160-278 cm in length) delphinid species(Stenella longirostris, S. attenuata, Tursiops aduncusandPeponocephala electra)to remote biopsy sampling in the vicinity of the island of Mayotte (12°50’S, 45°10’E, SW Indian Ocean). Two scales of behavioural reactions were considered: i) the behavioural reaction of the individual, and ii) the reaction of the focal group to which the targeted individual belonged. Three main categories of behavioural responses were defined on the basis of character and duration: low, moderate and strong. This study underlines that biopsy sampling induces moderate reactions in individuals. No inter-specific variations of responses, at the scale of the individual or focal group, were observed. In other words, smaller delphinids were not more reactive than larger ones. No effect of group size was observed on the strength of behavioural reactions. However, it was clear that biopsy success during sampling sessions was higher in species with large group size. Finally, in the spinner dolphin(S. longirostris), we investigated whether initial behavioural state affected the level of reaction. Resting and socialising groups showed a stronger response than milling and travelling groups. This study confirms the limited impact of remote biopsy sampling in small delphinids, especially in the spinner dolphin. However, as a precautionary approach, wherever possible, biopsy sampling of milling and travelling dolphins may be preferable.

Molecular insight into the population structure of common and spotted dolphins inhabiting the pelagic waters of the Northeast Atlantic

Several cetacean species exhibit fine-scale population structure despite their high dispersal capacities and the apparent continuity of the marine environment. In dolphins, most studies have focused on coastal areas and continental margins, and they revealed differentiated populations within relatively small geographic areas, sometimes in conjunction with a specialisation for different habitats (ecotypes). We analysed the population genetic structure of short-beaked common dolphins (Delphinus delphis) and Atlantic spotted dolphins (Stenella frontalis) in the Azores and Madeira, the two most isolated archipelagos of the North Atlantic. The archipelago of the Azores is divided into three groups of islands and stands 900 km away from Madeira. It is not known whether individuals migrate between groups of islands and archipelagos, nor whether distinct ecotypes are present. These questions were investigated by genetic analyses of 343 biopsy samples collected on free-ranging dolphins. The analyses consisted in sequencing part of the mitochondrial hyper-variable region, screening up to 14 microsatellite loci, and molecular sexing. Results did not unravel any population structure at the scale of the study area. Lack of differentiation matches expectations for spotted dolphins, which are transient in both archipelagos, but not for common dolphins, which are present year-round in the Azores and potentially resident. Absence of genetic structure over hundreds and even thousands of kilometres implies the existence of gene flow over much larger distances than usually documented in small delphinids, which could be achieved through individual movements. This finding indicates that population structure in oceanic habitat differs from that observed in coastal habitat.

Delphinid spatial distribution and abundance estimates over the shelf of the Bay of Biscay

AbstractCertain, G., Ridoux, V., van Canneyt, O., and Bretagnolle, V. 2008. Delphinid spatial distribution and abundance estimates over the shelf of the Bay of Biscay. – ICES Journal of Marine Science, 65: 656–666. The small delphinid community (bottlenose Tursiops truncatus, common Delphinus delphis, and striped Stenella coeruleoalba dolphins) of the Bay of Biscay (100 000 km2 of continental shelf along the French Atlantic coast) has been studied here by combining strip-transect aerial surveys conducted between 2001 and 2004 and ship-based surveys conducted between 2003 and 2006. Distribution was modelled spatially in relation to several large-scale descriptors of the environment. Highest densities of small delphinids were associated with the shelf break, in particular in two hotspots located in the north and the south of the bay. Using ship-based data, we found strong spatial segregation between common and bottlenose dolphins in spring, with common dolphins associated with coastal areas (and especially river plumes) and bottlenose dolphins on the outer shelf and the shelf break. Assuming a detection probability of 1, a strip-transect abundance estimate for the small delphinid community was obtained in August 2002 with 56 500 (95% CI 29 100–90 400), but relative abundance varied across months.