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Rationale: Stable isotope analysis of growth layers in sperm whale teeth dentine can provide valuable insight into individual long‐distance displacements and diet. Although treating teeth half‐sections with formic acid and rubbing their surface with a graphite pencil improves growth layer visibility and reduces sampling error, previous studies mostly used untreated half‐sections as the effect that this treatment may have on stable isotope ratios in dentine is unknown. The present study investigates the treatment effect on stable C and N isotope ratios in sperm whale teeth dentine. Methods: In the teeth of 30 sperm whales, we analysed and compared samples of powdered dentine obtained from (a) untreated half‐sections, (b) half‐sections etched with formic acid and rubbed with a graphite pencil and (c) half‐sections etched with formic acid from which the graphite pencil rubbing had been cleansed off. δ13$$ {\delta}^{13} $$C and δ15$$ {\delta}^{15} $$N values were compared between the three sample groups. Results: We found significant differences in values of both elements between untreated and etched samples, with a mean increase of 0.2% in δ13C and δ15N values in the etched samples. No significant differences were found between etched samples with graphite rubbing versus those without it. Significant linear regression models were calculated to predict untreated δ13C and δ15N values from the values obtained in the etched half‐sections with limited precision. Conclusions: We show for the first time that formic acid etching has a clear effect on δ13$$ {\delta}^{13} $$C and δ15$$ {\delta}^{15} $$N values in sperm whale teeth dentine. The developed models permit the estimation of untreated values from etched half‐sections, thus enabling the use of the latter in stable isotope analysis. However, as treatment procedures may vary between studies, it is advisable that similar predictive models are developed case‐by‐case to ensure comparability of results. [ABSTRACT FROM AUTHOR]

The Gulf of Ambracia, in northwestern Greece, hosts a highly threatened community of about 150 common bottlenose dolphins (Tursiops truncatus). Until now, information on their feeding habits was derived exclusively from fish scale samples collected during surface‐feeding events targeting small schooling epipelagic fish. The aim of this study was to determine the diet of bottlenose dolphins living in the Gulf of Ambracia through the application of Bayesian isotopic mixing models. Skin biopsy samples of 16 dolphins were analyzed and no difference related to sex or age‐class was found in δ13C and δ15N values. Results suggested that the dolphin diet was mainly based on Trachurus trachurus, species belonging to the family Sparidae: Diplodus annularis, Lithognathus mormyrus, and Sepia officinalis, which represented together about 42% ± 15% of the biomass ingested, followed by species belonging to the order Clupeiformes (Engraulis encrasicolus, Sardinella aurita, and Sardina pilchardus) and the genus Gobius (37% ± 17%). A better understanding of the feeding habits of these dolphins sheds light on the feeding ecology of this highly threatened population by, for instance, evidencing interactions with artisanal fisheries sharing the same target species, and is key for identifying adequate management measures consistent with an ecosystem‐based approach. [ABSTRACT FROM AUTHOR]

The fish‐eating, type‐C ecotype, killer whale is a top predator in the Ross Sea, Antarctica. Increasing knowledge of this animal's foraging habitats, diet and movement patterns is listed amongst the research priorities adopted under the framework of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).To contribute to this goal, satellite transmitters were deployed on 10 type‐C killer whales and skin biopsies were obtained from seven individuals in Terra Nova Bay (Ross Sea) during austral summer (January–February) 2015. Hierarchical switching state–space models (hSSSM) were applied to Argos satellite tracking data to describe the movements of tagged whales, which were then paired with available diving data. Stable isotopes analyses were performed on the biopsy samples to describe the diet.A total of 8,803 Argos locations were available to fit the hSSSM. All whales engaged in potential foraging activity in localized areas along the Ross Sea coastline, followed by uninterrupted travel (i.e. migration) outside Antarctic waters, with no evidence of foraging activity. The pattern of deeper dives matched the occurrence of encamped behaviour indicated by the hSSSM results. The stable isotopes analysis indicated that Antarctic toothfish comprised the largest component (35%) of the prey biomass, raising concerns since this species is targeted by commercial fishery in the Ross Sea Region.These results provide new insights into the ecology of type‐C killer whales in the Ross Sea Region, underlining a potential threat from commercial fishing in the area. Considering the recent establishment of the Ross Sea Region Marine Protected Area, these findings will contribute to the required Research and Monitoring Programme of the Marine Protected Area and provide new empirical evidence to inform conservation measures in the existing Terra Nova Bay Antarctic Special Protected Area. [ABSTRACT FROM AUTHOR]

Stable isotope analysis of whale skin has been recurrently used to assess diet and movement patterns. Such studies rely on the untested assumption that the stable isotope ratios in the small skin biopsies analysed are representative of those throughout the skin. In balaenopterids, the ventral skin looks notably different from that of the dorsal region, which is smoother and darker. To investigate possible differences in isotopic ratios throughout the skin, we collected and analysed samples from dorsal and ventral positions in 28 fin whales ( Balaenoptera physalus ). No significant differences were found between these two skin positions, which might suggest that whale skin is likely a homogeneous tissue. Thus, the isotopic ratios determined at a specific point may be representative of the whole skin in whales. [ABSTRACT FROM AUTHOR]

Rationale: Baleen plates are anatomical structures composed of inert tissue that hang from the upper jaw in mysticetes. Baleen plates may differ in size and in coloration between different segments of the filtering row or between sides of the mouth. Concern has been raised that variation in baleen plate characteristics may reflect dissimilar structural composition and growth rates liable to affect stable isotope ratios and their oscillation patterns. Methods: We measured stable carbon (δ13C values) and nitrogen (δ15N values) isotope ratios at intervals of 1 cm along the longitudinal axis of six baleen plates collected from different positions along the mouth of a fin whale. All samples were analysed using a continuous flow isotope ratio mass spectrometer. Generalized additive models were fitted to the data from each baleen plate and the results of the models were compared visually. Results: A total of 206 samples were analysed. Visually, all baleen plates presented nearly identical oscillations, independent of the position or the coloration of the baleen plate. However, the variation in δ13C and δ15N values occurring between the different baleen plates was higher in the segments of oscillations exhibiting steeper slopes. Conclusions: Differences in size between plates in an individual are due to differential erosion rates according to their position in the mouth. Therefore, the position of sampling along the baleen plate row should not be a reason for concern when conducting stable isotope studies. [ABSTRACT FROM AUTHOR]

The Sundarbans forest is the largest and one of the most diverse and productive mangrove ecosystems in the world. Located at the northern shoreline of the Bay of Bengal in the Indian Ocean and straddling India and Bangladesh, the mangrove forest is the result of three primary river systems that originate further north and northwest. During recent decades, the Sundarbans have been subject to increasing pollution by trace elements caused by the progressive industrialization and urbanization of the basins of these three rivers. As a consequence, animals and plants dwelling downstream in the mangroves are exposed to these pollutants in varying degrees, and may potentially affect human health when consumed. The aim of the present study was to analyse the concentrations of seven trace elements (Zn, Cu, Cr, Hg, Pb, Cd and As) in 14 different animal and plant species collected in the Sundarbans in Bangladesh to study their transfer through the food web and to determine whether their levels in edible species are acceptable for human consumption. δ 15 N values were used as a proxy of the trophic level. A decrease in Zn, Cu, Pb and Cd levels was observed with increasing trophic position. Trace element concentrations measured in all organisms were, in general, lower than the concentrations obtained in other field studies conducted in the same region. When examined with respect to accepted international standards, the concentrations observed in fish and crustaceans were generally found to be safe for human consumption. However, the levels of Zn in Scylla serrata and Cr and Cd in Harpadon nehereus exceeded the proposed health advisory levels and may be of concern for human health. [ABSTRACT FROM AUTHOR]

From the early 17th century to the 1970s southern right whales, Eubalaena australis, were subject to intense exploitation along the Atlantic coast of South America. Catches along this coast recorded by whalers originally formed a continuum from Brazil to Tierra del Fuego. Nevertheless, the recovery of the population has apparently occurred fragmentarily, and with two main areas of concentration, one off southern Brazil (Santa Catarina) and another off central Argentina (Peninsula Valdés). This pattern suggests some level of heterogeneity amongst the population, which is apparently contradicted by records that traced individuals moving throughout the whole geographical extension covered by the species in the Southwest Atlantic. To test the hypothesis of the potential occurrence of discrete subpopulations exploiting specific habitats, we investigated N, C and O isotopic values in 125 bone samples obtained from whaling factories operating in the early 1970s in southern Brazil (n = 72) and from contemporary and more recent strandings occurring in central Argentina (n = 53). Results indicated significant differences between the two sampling areas, being δ13C and δ18O values significantly higher in samples from southern Brazil than in those from central Argentina. This variation was consistent with isotopic baselines from the two areas, indicating the occurrence of some level of structure in the Southwest Atlantic right whale population and equally that whales more likely feed in areas commonly thought to exclusively serve as nursing grounds. Results aim at reconsidering of the units currently used in the management of the southern right whale in the Southwest Atlantic Ocean. In the context of the current die-off affecting the species in Peninsula Valdés, these results also highlight the necessity to better understand movements of individuals and precisely identify their feeding areas. [ABSTRACT FROM AUTHOR]

From the early 17th century to the 1970s southern right whales, Eubalaena australis, were subject to intense exploitation along the Atlantic coast of South America. Catches along this coast recorded by whalers originally formed a continuum from Brazil to Tierra del Fuego. Nevertheless, the recovery of the population has apparently occurred fragmentarily, and with two main areas of concentration, one off southern Brazil (Santa Catarina) and another off central Argentina (Peninsula Valdés). This pattern suggests some level of heterogeneity amongst the population, which is apparently contradicted by records that traced individuals moving throughout the whole geographical extension covered by the species in the Southwest Atlantic. To test the hypothesis of the potential occurrence of discrete subpopulations exploiting specific habitats, we investigated N, C and O isotopic values in 125 bone samples obtained from whaling factories operating in the early 1970s in southern Brazil (n = 72) and from contemporary and more recent strandings occurring in central Argentina (n = 53). Results indicated significant differences between the two sampling areas, being δ13C and δ18O values significantly higher in samples from southern Brazil than in those from central Argentina. This variation was consistent with isotopic baselines from the two areas, indicating the occurrence of some level of structure in the Southwest Atlantic right whale population and equally that whales more likely feed in areas commonly thought to exclusively serve as nursing grounds. Results aim at reconsidering of the units currently used in the management of the southern right whale in the Southwest Atlantic Ocean. In the context of the current die-off affecting the species in Peninsula Valdés, these results also highlight the necessity to better understand movements of individuals and precisely identify their feeding areas. [ABSTRACT FROM AUTHOR]

RATIONALE The relationship between stocks of fin whales inhabiting the temperate eastern North Atlantic and the Mediterranean Sea is subject to controversy. The use of chemical markers facilitates an alternative insight into population structure and potential borders between stocks because the two areas present dissimilar isotopic baselines. METHODS Baleen plates, composed of inert tissue that keeps a permanent chronological record of the isotopic value of body circulating fluids, were used to investigate connectivity and boundaries between the stocks. Values were determined by continuous flow isotope ratio mass spectrometry. RESULTS Stable isotopes confirm that, while the two subpopulations generally forage in well-differentiated grounds, some individuals with characteristic Atlantic values do penetrate into the Mediterranean Sea up to the northernmost latitudes of the region. As a consequence, the border between the two putative subpopulations may be not as definite as previous acoustic investigations suggested. The discriminant function obtained in this study may assist researchers to use baleen plate isotopic data to assign the origin of fin whales of uncertain provenance. CONCLUSIONS This study strengthens the stock subdivision currently accepted for management and conservation while recognizes a low level of exchange between the Mediterranean and temperate eastern North Atlantic subdivisions. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

[Display omitted] • δ13C, δ15N and δ34S were analysed in skin from 5 Icelandic baleen whale species. • MixSiar model showed that krill was the main prey for all species except common minke whales. • In humpback whales, dependence on krill may reduce entanglement risk in fishing gear. • Isotopic niche overlap between species was small, except between blue and fin whales. • Niche overlap between fin and blue whales suggests strong interspecific competition. The highly productive waters off Iceland are an important feeding ground for baleen whales. Five balaenopterid species coexist there during the summer feeding season: the blue whale, the fin whale, the sei whale, the humpback whale and the common minke whale. For capital breeders such as baleen whales, niche partitioning and reduced interspecific competition during their stay in the feeding grounds may be critical for the completion of their annual cycles and the long-term stability of populations. Coexistence often entails spatio-temporal or trophic segregation to avoid competitive exclusion. With the aim of studying how these species share habitat and trophic resources, we analyzed the δ13C, δ15N and δ34S values in skin samples. Bayesian stable isotope mixing models to calculate compositional mixture of food sources showed that most species segregate by consuming different prey. Segregation was further enhanced by some degree of spatio-temporal exclusion. Overall, clear ecological niche partitioning was apparent between all species except between blue and fin whales. All the species consumed krill and, except for the common minke whale, this was the dominant prey. Among baleen whales, common minke whales and humpback whales were the major predators of sand eel, capelin and herring. In humpback whales, a strong reliance on krill may explain the apparently low rates of local entanglement in fishing nets as compared to other areas. Except for the blue whale, all species have shown evidence of adapting to shifts in prey availability and thus suggested capacity to cope with variability. However, in a scenario of increasing environmental variability associated to global warming, the overlap between ecological niches may have to decrease to allow long-term coexistence. [ABSTRACT FROM AUTHOR]

We investigated the sex- and size-related differences in the diet of whale sharks from the Arabian Sea (north-western Indian Ocean) using carbon and nitrogen stable-isotope analyses in white muscle. The samples were collected during the commercial fishing season between April and May of 2001 in Veraval (Gujarat, India). The overall isotope signature was similar to that of the pelagic-neritic zooplanktivore Ilisha melastoma, which suggests that both species are feeding on similar prey. In whale sharks, a positive relationship was found between δN and δC. This, together with a significant enrichment of both heavy stable isotopes with total length indicates that the contribution to the diet of small fish and/or larger zooplankton of higher trophic level increases with the movement from offshore areas to coastal areas as they grow. Gender differences in the isotopic ratios were not statistically significant, but small sample size cannot rule out completely the existence of some degree of spatial or dietary segregation between sexes. [ABSTRACT FROM AUTHOR]

[Display omitted] • The conservation status of Mediterranean cetaceans is cause of concern. • δ13C, δ15N and δ34S isotopic niches were calculated for five species of cetaceans. • Overlaps between isotopic niches were generally small. • Most of the species avoided competitive exclusion. • Niche overlap of striped and common dolphins suggested interspecific competition. Ten species of cetaceans coexist in the Mediterranean Sea, one of the richest seas in biodiversity and endemisms worldwide. The conservation status of Mediterranean cetaceans has been a concern for many years, particularly due to increasing anthropogenic threats such as global warming and overfishing. We established the stable isotopic niches of carbon, nitrogen, and sulphur for five species of cetaceans inhabiting the northwestern Mediterranean Sea to elucidate the mechanisms of coexistence. The fin whale exploited epipelagic habitats with a low trophic level; the bottlenose dolphin was mostly neritic and had a high trophic level; the Risso's dolphin was oceanic and fed bathypelagically and at a high trophic level; finally, the common and striped dolphins displayed epipelagic distributions and similarly intermediate trophic levels. The isotopic niches of all species were exclusive except the common and striped dolphins, whose niches overlapped by 20%. These results suggest that the majority of species avoid competitive exclusion by trophic or spatial segregation with the exception of striped and common dolphins, in which interspecific competition is apparent. It is suggested that this competition brought the striped dolphin to displace the common dolphin from part of its distribution range, restricting it to the southern fringe of the western Mediterranean and, particularly, to the Alboran Sea. In this area, coexistence of the two species would be permitted by some degree of spatial segregation between them and a remarkably high productivity, all which mitigate competition. [ABSTRACT FROM AUTHOR]

Highly migratory marine species pose a challenge for the identification of management units due to the absence of clear oceanographic barriers. The population structure of North Atlantic fin whales has been investigated since the start of whaling operations but is still the subject of an ongoing scientific debate. Here we measured stable isotopes of carbon, nitrogen and oxygen in skin samples collected from 151 individuals from western Iceland, Galicia (NW Spain), the Azores archipelago and the Strait of Gibraltar (SoG). We found spatiotemporal differences in stable isotope ratios suggesting that fin whales sampled in these four areas may share a common feeding ground within the Northeast Atlantic at different times during the year. Our results also suggest that SoG whales use this common feeding ground in summer but exploit Mediterranean resources during the winter months, further supporting the existence of a limited but current exchange of individuals between these two basins. • δ 13C, δ 15N and δ 18O values were measured in fin whale skin from four North Atlantic areas. • Spatiotemporal differences were found in the stable isotope profiles. • All whales may share a common Atlantic feeding ground at different times during the year. • Gibraltar whales use this common feeding ground in summer but the Mediterranean in winter. [ABSTRACT FROM AUTHOR]

In pelagic species inhabiting large oceans, genetic differentiation tends to be mild and populations devoid of structure. However, large cetaceans have provided many examples of structuring. Here we investigate whether the sperm whale, a pelagic species with large population sizes and reputedly highly mobile, shows indication of structuring in the eastern North Atlantic, an ocean basin in which a single population is believed to occur. To do so, we examined stable isotope values in sequential growth layer groups of teeth from individuals sampled in Denmark and NW Spain. In each layer we measured oxygen- isotope ratios (δ18O) in the inorganic component (hydroxyapatite), and nitrogen and carbon isotope ratios (δ15N: δ13C) in the organic component (primarily collagenous). We found significant differences between Denmark and NW Spain in δ15N and δ18O values in the layer deposited at age 3, considered to be the one best representing the baseline of the breeding ground, in δ15N, δ13C and δ18O values in the period up to age 20, and in the ontogenetic variation of δ15N and δ18O values. These differences evidence that diet composition, use of habitat and/or migratory destinations are dissimilar between whales from the two regions and suggest that the North Atlantic population of sperm whales is more structured than traditionally accepted. [ABSTRACT FROM AUTHOR]

It is commonly assumed that the resolution of the isotopic niche of consumers can be improved with a larger number of chemical elements, but this is only true if steep environmental gradients exist at the appropriate spatial scale. Off Mauritania, the δ13C value is a useful proxy to understand the distribution of marine mammals along the inshore-offshore gradient, and the δ15N value to assess their trophic position. Here, the incorporation of δ18O values as an independent habitat tracer largely improved the resolution of the isotopic niche, because the δ18O gradients, mostly reflecting marked salinity gradients, spanned over broad spatial scales when compared to the home range of marine mammals. On the contrary, δ34S values did not improve much the resolution of the isotopic niche at the species level, although it was useful to identify individuals relying on food webs associated with anoxic sediments, such as seagrass meadows. This is because the δ34S gradient in the area develops over a small spatial scale, compared to the home range of the considered species. This study provides new insights into the use of a muti-element approach in isotopic ecology, and improves the understanding of habitat partitioning between the considered marine mammal species off North Western Africa. [Display omitted] • δ18O and δ34S complement δ13C as habitat tracers, but at different scales. • δ18O is useful to identify species using water mases of contrasting salinity. • δ34S is useful to identify individuals within a species relying on seagrass meadows. • Sighting and stranding reports validate inferences made from stable isotope ratios. • The gradient of the isotopic tracer should encompass the home ranges of the species. [ABSTRACT FROM AUTHOR]