Despite attacks of bottlenose dolphins towards conspecifics and other species of dolphins being reported worldwide, inside the Mediterranean Sea these behaviours are still considered sporadic and have been, to date, only recorded in Spain and France, mostly directed to striped dolphins. In this work, we reported the necropsy outcomes of a dead striped dolphin that suggest a fatal interaction with bottlenose dolphins inside the Italian side of the Pelagos Sanctuary, Western Ligurian Sea. Results from the post-mortem examination showed multiple, multifocal external rake marks spaced 1–1.2 cm and several internal injuries, consisting of subcutaneous and muscular haematomas and haemorrhages, multiple vertebral and rib fractures, haemothorax and lung laceration. The inter-tooth distance and all the internal findings were consistent with a fatal traumatic interaction with bottlenose dolphins as reported in similar cases in other parts of the world where the same results were found. No other significant gross and microscopic findings and concurrent significant pathogens were detected. This case highlights the existence of negative interspecific interactions in an area where they have never been reported before and adds new important information to the literature for understanding their occurrence, expanding the geographical range of observation in the western Mediterranean Sea.

Stomach contents of six striped dolphins taken as by-catch in the swordfish fishery in the eastern Mediterranean Sea off the Turkish coast were examined. In total, 29 taxa were identified to species or family and 1777 individual food items (1394 bony fishes, 289 cephalopods, 94 crustaceans) were counted. Diaphus spp. and Ceratoscopelus maderensis were the most remarkable ones, as they accounted for 70.45% of the total number of fishes. Onychoteuthis banksii, on the other hand, was the only cephalopod species found in all stomach content analyses and represented 38.06% of the total number of cephalopods. Bony fish species: Myctophum punctatum, Notoscopelus elongatus, Electrona risso, Sudis hyalina, Moridae sp., Phycidae sp., Sternoptychidae sp. and cephalopods: Pterygioteuthis giardi and Chtenopteryx sicula were reported the first time in the stomach contents of striped dolphin in the Mediterranean Sea.

The feeding ecology of striped dolphin, Stenella coeruleoalba, in the north-western Mediterranean Sea was studied using stable isotope analyses. Carbon and nitrogen stable isotope ratios were measured in skin and muscle tissues of stranded and by-caught dolphins from six geographical areas in the Mediterranean Sea and Atlantic Ocean. Variation in δ15N in relation to dolphin size is attributed to changes in diet. Nursing calves have a higher trophic level than weaned animals and their δ15N values decrease progressively until weaning, estimated to be at a body length of around 155 cm. δ15N values then increased for larger individuals which suggests changes in diet for mature dolphins. Geographical differences in diet were apparent between the Atlantic and the Mediterranean, although no clear differences were apparent between the five Mediterranean areas. Comparisons of the nitrogen isotope ratios of skin and muscle highlighted a higher fractionation in skin compared to the muscle tissue. Values of δ13C also increased with body length although it appears that this is not only driven by trophic level enrichment. δ13C increases before weaning and the difference in trophic level between newly-weaned and mature dolphins was twice as high for carbon as for nitrogen. Ontogenetic changes in carbon isotope composition may therefore be driven by feeding on deep water prey and dolphin movements outside the coastal feeding grounds. Indeed, seasonal variations in δ13C are suspected to be driven by migration within the Mediterranean basin.

The present contribution reports for the first time the sessile barnacle Xenobalanus globicipitis as an epizoic of the striped dolphin Stenella coeruleoalba in the oligotrophic waters of north-eastern Brazil. One barnacle specimen was found on a dead cetacean in Ceará State, north-eastern Brazil. Diagnosis and figures of the barnacle are provided and the relationship between the epizoic and the host discussed.

Regular monitoring of the status of cetacean populations is essential for conservation, policy and management. By using a passenger ferry as a scientific research platform, this study provides information on seasonal, annual and longer-term changes in the occurrence of three cetacean species along a relatively fixed transect through the English Channel and the Bay of Biscay. Data were collected over an 11 year period through the Biscay Dolphin Research Programme (BDRP). Surveys were conducted every month from 1996–2006 between Portsmouth, England and Bilbao, Spain by a team of experienced observers using standard techniques. From a 0.125° by 0.125° grid, cells were surveyed in each year and where each species was recorded they were identified using a geographical information system (GIS). A rapid analytical method—species occupancy (defined as the proportion of surveyed cells that a species was detected in)—was used to assess whether there were any trends in occurrence over time for three cetacean species. From this analysis, a significant trend to increasing occurrence of harbour porpoises in summer months in the English Channel was identified. There were also increases in the occurrence of common dolphins in the English Channel in winter months and striped dolphins in the Bay of Biscay in winter months corresponding with a decrease in summer occurrence, across the study period. However, while consistent, these trends were not significant.

Studies on differences in external morphology and pigmentation patterns were historically carried out using stranded individuals or opportunistic sightings; few studies have involved sampling systematically free-ranging individuals. In order to investigate and describe main pigmentation characteristics, outlining ‘typical’ regional pigmentations, this work analysed systematic photographic information taken on free-ranging striped dolphins, Stenella coeruleoalba. Photographs of dolphins in the Ligurian Sea were collected between May 2004 and December 2006. All individuals were described by the presence/absence of pigmentation variables and by differences in colour shades. The frequency of all the pigmentation variables analysed is stable in the population (10 ‘gene’ variables, 19 ‘allele’ variables), and remains similar between each different group of dolphins. But population presents widespread pigmentation variability between specimens, allowing identification even at single individual level. Cluster analysis also found that the majority of the pigmentations derive from two main colour patterns, called ‘mat’ and ‘pale’ patterns (fmat = 0.68; fpale = 0.12). The Bray–Curtis index showed a high variability of the intra-group pigmentation distance between groups. This resulted in a positive correlation between group size and ‘intra-group’ pigmentation distance: the distance increases rapidly up to a group size of 40 individuals. According to the results obtained, the striped dolphins seem to be concentrated in small groups in which there is a large phenotypic similarity among individuals. These small units could be associated between them to form temporary large groups observed only in pelagic waters.

Habitat distribution models are one of the most up to date methods to study the habitat usage of wildlife populations. They allow animal distribution to be related to environmental features and also the prediction of the distribution of animals based on this relationship. Seasonal aerial surveys were conducted in central Spanish Mediterranean waters from June 2000 to March 2003 to obtain information on the distribution of cetacean species. Data from the three most common cetacean species (striped dolphin, Stenella coeruleoalba, bottlenose dolphin, Tursiops truncatus, and Risso's dolphin, Grampus griseus) were related, using generalized linear models, to local environmental features: depth, slope, sea surface temperature and chlorophyll concentration. For bottlenose dolphins, no significant relationship was found with any covariate and no dolphins were observed in waters greater than 1000 m. The distribution of both striped and Risso's dolphin was significantly related to depth. The striped dolphin showed a preference for waters between 900 and 1500 m deep and Risso's dolphin for waters more than 1500 m deep. In addition, for the latest two species, maps of distribution were predicted by means of the spatial models. The areas of higher probabilities of occurrence coincide to a large extent with the marine protected areas previously proposed for the conservation of oceanic cetacean species.

During 1992–2003, 52 striped dolphin strandings were recorded in Scotland (UK). Although strandings were recorded in every month of the year, highest numbers were found in January–March and August. Striped dolphins were stranded all around the Scottish coast, but the majority were recovered from the west coast. Necropsies were carried out on 33 of these animals: 29 had live-stranded and cause of death was not established for four animals. Stomach contents were analysed for 20 animals: whiting and Trisopterus were the main prey species in the diet (both by number and by reconstructed biomass). Females had a higher average number of Trisopterus in their stomachs than did males. Trisopterus eaten in winter were larger than Trisopterus eaten in summer and both Trisopterus and whiting eaten on the east coast were bigger than those eaten on the west coast. The reproductive status was determined for six females and six males during 2001–2003, with the majority being immature but the sample included one pregnant female and one sexually active mature male. We calculated the length–weight relationship for this species in Scottish waters. In addition, age data were collected from samples obtained during necropsies on six striped dolphins: the oldest dolphin sampled was around 14 y old but the majority were 2–7 y old. Although the numbers are low, the regular occurrence of stranded striped dolphins in recent years around Scotland, suggests that this warm water species may now be considered resident in Scottish waters.

Two types of tetraphyllidean merocercoids, Phyllobothrium delphini and Monorygma grimaldii, are well known from most cetaceans world-wide. The role of cetaceans in the life-cycle of these merocercoids is unclear because their specific identity is as yet unknown. The problem is compounded by poor descriptions of both merocercoids. We used light and scanning electron microscopy, and histological techniques to provide a thorough description of merocercoids collected from 11 striped dolphins, Stenella coeruleoalba, from the Spanish Mediterranean. We also described, for the first time, specimens of P. delphini with immature proglottides. Our merocercoids were morphologically similar to those described previously, except in the structure of the apical organ. Intra- and inter-sample variability in the morphology of the apical organ suggested that it degenerates during larval development. A subsample of 16 specimens of P. delphini and M. grimaldii was characterized for the D2 variable region of the large subunit ribosomal RNA gene (LSU) and compared with published tetraphyllidean cestode LSU sequences. P. delphini showed 2 unique signatures that differed from one another by a single base, whereas all sequences of M. grimaldii were identical. This suggests that each type may represent a single species, contrary to previous speculations based on morphological data. All merocercoid specimens formed a clade together with Clistobothrium montaukensis. Based on the low degree of divergence, all specimens of this clade are predicted to be congeneric.