The coast of Aragua is a home of bottlenose dolphins (BND), Atlantic spotted dolphins (ASD) and fishermen (FIS) from four towns. A photo-identification study was carried out on BND to estimate their home ranges. From 2004 to 2008, 100 field surveys were carried out along 30 km of coastline (92.12 km2). In each sighting of BND, information regarding date, time, latitude/longitude and photographs were registered (ASD and FIS were registered without photography). The data were analysed using a Geographic Information System to estimate Minimum Convex Polygon (MCP) and Fixed Kernel (FK) at 95%. The home ranges of BND were estimated for seven individuals. This included three females (29–31 sightings) with estimated areas ranging from 33.90–39.90 km2 with MCP (36.79–43.31% of the study area) and from 80.47–101.31 km2 with FK (109.97–104.26%). For the remaining four dolphins (14–20 sightings) the estimated areas ranged from 9.67–22.34 km2 (MCP), the predominant depth of these home ranges varied from 51–100 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). For the pods of ASD the estimated area ranged 75.23 km2 with MCP (81.66%) and 119.86 km2 with FK (130.11%) with predominant depths of 101–200 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). The area used by FIS ranged 93.27 km2 by MCP and 228.49 km2 by FK. Finally, the overlap area of BND, ASD and FIS ranged 24.75 km2 (26.86%). We point out this locality presents important oceanographic and ecological aspects which deserve to be the subject of application of management plans for the conservation of its habitat and species.

Bottlenose dolphins (Tursiops truncatus) have been surveyed for at least two decades on the southern Brazilian coast. However, little is known about their distribution and habitat use in lower latitudes of the South-western Atlantic Ocean. Aiming to study the movements and distribution of the species along the south-eastern Brazilian coast, we made a comparison of photo-identified individuals of the species catalogued in 21 cruises conducted between 2012 and 2015. Additionally, we performed stable isotope analyses of carbon and nitrogen in skin samples (N = 35) to provide some insights of dolphin habitat use and trophic ecology through comparisons among individuals of distinct surveyed sectors (northern and southern) and sex. A total of 177 individuals were identified. Re-sightings (N = 24) occurred at intervals from 82 to 979 days at distances from 7 to 179 km. No individual was sighted in both sectors, suggesting spatial segregation. Isotopic comparisons showed no significant differences in carbon and nitrogen signatures between distinct sectors. However, ecological divergences were found when we divided the samples by gender. Wider isotopic niches were found for the northern bottlenose dolphins vs the southern ones, which could be related to temporal and spatial variation in the availability of resources, as well as possible differences in the home ranges of males and females in each region. This study represents a preliminary evaluation of ecological aspects of bottlenose dolphins along the Brazilian south-eastern coast, however, long-term studies on the feeding ecology and habitat use of this species are important to further improve our knowledge.

Rough-toothed dolphins (Steno bredanensis) are regularly present in continental shelf areas of the South-western Atlantic. However, there is little information on the natural history and ecology of these delphinids. This study evaluated the occurrence, habitat use and individual movements of the species in coastal waters off Rio de Janeiro, south-eastern Brazil. Data were obtained from boat surveys between August 2011 and May 2018, during which rough-toothed dolphins were sighted in 21 distinct events, predominantly in autumn and winter. The mean group size was 29 individuals. Rough-toothed dolphins were usually recorded 130 to 2300 m from the coast, between 7.6 and 28 m depths. In total, 115 individuals were catalogued through dorsal fin marks and 61 (53%) were resighted between one (47.5%) and four (9.8%) occasions. The interval between resightings ranged from seven to 2087 days (mean = 268). Agglomerative hierarchical clustering indicated 30 individuals (49.2%) in low degree, 12 (19.7%) in medium degree and 19 (31.1%) in high degree of site fidelity. Dolphins showed a higher frequency of low degree of habitat use, despite the presence of multiyear recaptures, which may be related to the prevalence of dolphin occurrence in autumn and winter, a large home range and/or the abundance and distribution of food resources. Dedicated surveys and regional collaboration are needed to evaluate the home range and population status of this species for their effective conservation. Our findings enhanced knowledge of this little studied species facing increasing anthropogenic threats in coastal waters off Rio de Janeiro.

This study focuses on the dolphins populating the water between Gibraltar and Algeciras in the south Iberian Peninsula, an area subjected to pressure due to high human activity. The area is considered an important feeding and breeding ground for common dolphins (Delphinus delphis). Due to the degree of residence of some specimens, and the large gap in knowledge about the evolution of wounds in D. delphis specimens with lacerations, this work sought to perform the following analyses: identify lacerated individuals; characterize sequences of ‘before – during – after’ with respect to the occurrence of lacerations; and associate the type of injury with its severity. This work will inform future studies by expanding a database on injured individuals and contribute to periodical monitoring of specimens that frequent these geographic areas. Between 2013 and 2017, we were able to track the healing process of five injured individuals of common dolphins from a whale-watching platform thanks to photo identification. The animals exhibited fresh external wounds from different sources. In the majority of individuals, the wound-healing processes lasted 3–21 weeks. The frequency with which sightings are made and knowledge about the local population will help track injured animals, follow their wound evolution, and document their survival rates. The documented injuries inflicted by human interactions described in this paper may include fishing interactions and propeller strikes, probably as a consequence of the high intensity of recreational fishing and whale-watching activities in the area.

The coastal waters of east Lewis from the Butt of Lewis to Loch Erisort are a proposed Marine Protected Area (MPA) for Risso's dolphins (Grampus griseus). A total of 100.4 h (2006.4 km) of active search effort (Beaufort sea states ≤3) was collected during 72 dedicated boat surveys between 2010 and 2017 (primarily in August and September) in the southern part of the MPA and south to the Shiant Isles. Forty Risso's dolphin sightings and 24.1 h of encounter effort were recorded, predominantly along the southern and eastern Eye Peninsula in 20–40 m water depths and at distances <1 km from shore. Group size ranged from one to 50 animals (mean = 11.8 dolphins) and calves occurred in 37.5% of sightings. A total of 2404 shore-based scans (Beaufort sea states ≤3) carried out from Tiumpan Head between September 2011 and December 2017 resulted in 271 (11.3%) ‘dolphin-present’ scans. Dolphins were present year-round, with a seasonal increase between May and October. ‘Calf-present’ scans only occurred between April and October. Photo-identification images from 28 boat surveys produced a minimum population size of 117 animals. There was evidence of high inter- and intra-annual site fidelity, with individual dolphins photographically captured in up to six of the eight survey years, and between two and seven capture dates being recorded for over 45% of individuals within most years. The combined datasets support the importance of east Lewis for Risso's dolphins, and recommendations are made for ongoing monitoring of dolphin occurrence throughout the wider MPA.

The bottlenose dolphin (Tursiops truncatus M.) local population off west Istria in the North-eastern Adriatic has received no prior study of abundance and distribution despite the habitat's relevance for the preservation of this key species in the marine ecosystem. The research area comprises part of the NATURA 2000 network which was predominantly established here for these dolphins. Official data regarding the local population's status in the region are currently marked as deficient. Thus, the aim of the present study was to provide the first population data for the area. Boat-based survey work was carried out from April to September 2012–2015 using a mark–recapture photo-identification method. Prior to this period a random data collection was used to study distribution, since 2001, to cover the area of 927 km2 lying between Umag to lighthouse Albanež in the south. 143 bottlenose dolphins were photo-identified to date with the average group size of 9.27 ± 6.53 animals. Several abundance models were used, from which the Markovian robust model proved the best fit and predicted between 47–142 dolphins along the west Istria coast. A few individuals were also identified in Slovenia, indicating a bigger home range along the 98 km length of the studied area. There is an indication of a regular year round presence of dolphins. The west Istria coast constitutes an important feeding and breeding ground. The region should develop a sustainable plan to manage those human activities negatively impacting the dolphins. Therefore the present study is of relevance for the implementation of management directives for their conservation.

The Arabian Gulf is one of the most heavily impacted water bodies raising serious concerns about the conservation status of many marine species. A limited coastal range and near-shore distribution make Indian Ocean humpback dolphins particularly vulnerable to mortality and traumatic injuries from heavy maritime traffic and gill-netting practices. Prior to the present study, no research had focused on the ecology of this species in the Arabian Gulf, despite the potential for human impacts. The mark–recapture method of photo-identification, undertaken during 55 boat-based surveys conducted between 2014 and 2015, was used to assess the occurrence, abundance and use of habitat of this endangered species along the coast of the Emirate of Abu Dhabi (UAE). In all, 368 h and 6703 km of observation were carried out over a period of 5 months, and 54 encounters were made with humpback dolphins. The group size ranged from 1 to 24 individuals and group composition showed that 79% of the observed dolphins were adults. Abundance estimates were calculated and fitted with open population models. A review of all available data indicates that the studied population is the largest reported in the world with 701 (95% CI = 473–845) individuals. While their occurrence within Abu Dhabi near-shore waters is frequent, the survey area appears to be only a part of a much larger home range for this humpback dolphin population. The observation of multiple threats derived from anthropogenic activities increases our concerns regarding the conservation of this important dolphin population.

In order to investigate social structure, 11 years of individual photo-identification data of bottlenose dolphin were analysed. We examined the type of association indices between pairs of identified individuals; the patterns of affiliation between individual dolphins and the probabilities of association between individuals over time. Between 2001 and 2012, there were 272 encounters which resulted in the identification of 501 individuals. The discovery curve resulting from the photo-identification analysis indicated an open population with regular recruitment of new individuals. All individuals were found to be associated at an association index of <0.05. A total of 291 individuals recorded from 2004 to 2012 were used to assess the temporal pattern of the social structure. The model fit to the Standardized Lagged Association Rate (SLAR) that best described the studied bottlenose dolphin population was ‘casual acquaintances’, and the analysis of associations over time showed a decreasing SLAR curve that falls until reaching the null rate, confirming random associations. The decline of the SLAR curve after ~500 days (1.4 years) suggests disassociation over that time period which can be explained by demographic events such as mortality or emigration. In an open ocean habitat like Madeira this is not unexpected, as there are neither geographic boundaries nor enclosed environments. This population presented a dynamic and fluctuating social structure, where groups change in size and composition. In future conservation efforts this population should be considered as one large community, where individuals associate, disassociate and reassociate with each other over time.

In this study photo-identification data were used to better understand movements, population structure and abundance of common bottlenose dolphin (Tursiops truncatus) in south-west England and surrounding waters, to inform conservation efforts. A catalogue of 485 photographic sightings of 113 individuals was compiled from ~150 common bottlenose dolphin encounters made on 87 dates between March 2007 and January 2014. From these and other data, three likely sub-populations were identified in the western English Channel, demarcated by bathymetry and distance to land: (1) south-west England – inshore Cornwall to Devon, (2) offshore English/French waters and (3) inshore France from Brittany to Normandy. Maximum abundance estimates for south-west England coastal waters, using two methods, ranged between 102 and 113 (range 87–142, 95% CL) over the period 2008–2013, likely qualifying the region as nationally important, whilst the yearly maximum was 58 in 2013. The population was centred on Cornwall, where 19 well-marked animals were considered ‘probable’ residents. There were no ‘probable’ resident well-marked individuals found to be restricted to either Devon or Dorset, with animals moving freely within coastal areas across the three counties. Movements were also detected within offshore English waters and French waters (from other studies) of the western English Channel, but no interchange has as yet been detected between the three regions, highlighting the possible separation of the populations, though sample sizes are insufficient to confirm this. Given the findings, south-west England waters should be considered as a separate management unit requiring targeted conservation efforts.

In species that aggregate for reproduction, the social and fitness costs of movement between groups frequently lead to restricted exchange between breeding areas. We report on four individual humpback whales identified in both the Cape Verde Islands and Guadeloupe; locations separated by an ocean basin and >4000 km. This rate of exchange is rarely encountered between such geographically discrete breeding areas. Two individuals returned to the area where they were originally identified. In contrast, no individuals from the Cape Verde Islands were resighted to the much larger sample from the Dominican Republic, though the migratory distances from the feeding areas are comparable between these areas. The social factors driving the stark difference between groups that is observed here are not clear. Effective conservation requires an understanding of the extent and pattern of movement between population units. The findings presented here suggest that there may well be more than one behaviourally distinct group within the West Indies. More broadly, they argue that considerable caution is warranted in assumptions made regarding the number, boundaries and status of population units based solely on spatial separation or proximity.

Understanding animal movement patterns is not only important for providing insight into their biology, but is also relevant to conservation planning. However, in aquatic and wide-ranging species such as cetaceans, this is often difficult. The common bottlenose dolphin (Tursiops truncatus) is the most common cetacean in the northern and central Adriatic Sea and has been the focus of long-term studies in some areas. All of the studied local populations show a relatively high degree of site fidelity, but their movements, ranging patterns or connectivity are not well understood. On 24 and 26 April 2014 a single adult bottlenose dolphin was observed and photographed alive off the Slovenian coast. The same individual was found dead on the shores of Goro, Italy, on 5 May 2014, about 130 km from the two sighting locations. The well-marked dorsal fin made the identification straightforward. The dolphin was found freshly dead, suggesting it had died very recently prior to being found. This indicates that the reported movement was a real one, rather than an artefact of currents. Although single cases cannot provide the basis for making population-level inferences, our observation shows that northern Adriatic bottlenose dolphins can make substantial movements in short periods of time and suggests that such movements could be more common than currently documented. Comparisons among photo-ID catalogues and stranding events can be highly informative, as they can provide useful information with implications for the cross-border conservation of mobile marine predators.

In the present study, short-beaked common dolphins (Delphinus delphis L.) from the Bay of Gibraltar (GIB) and the Moray Firth (MF) were examined to document the relative frequency, distribution and shape of dorsal edge markings (DEMs) in the species and investigate potential causes for their occurrence. A dorsal fin layout system was used to map the relative positions and shapes of presenting DEMs along the anterior/posterior and upper/lower fin margin from 617 animals. A total of 1989 DEMs were extracted from the combined datasets, with individuals exhibiting between one and 11 nicks (median = 3). DEMs (in the form of tears, nicks, notches and indents) were primarily observed along the posterior trailing edges of fins, with the highest concentration being recorded in the upper region of the posterior fin (80.3%). Approximately 80% of all DEMs were round or rectangular in shape. Square (notched) and indented nick shapes were further recorded, but in significantly lower numbers. In contrast to all other nick shapes however, indented DEMs predominantly occurred along the anterior fin margin. Both natural and anthropogenic sources were implicated as causes of DEMs in the dataset. Interactions with fisheries were apparent in both GIB and MF animals and evidently present a threat to both populations. Indeed, the occurrence, prevalence and type of presenting DEM and/or fin injuries (e.g. missing fins or disfigurements) in the species may provide a useful measure of the type and intensity of fisheries interactions affecting different populations.

Natural marks occurring in cetaceans are used to measure population parameters, social structure and movements. However, the changeable nature of these marks can originate bias in these estimates. The aim of this work was to calculate abundance and prevalence of 28 mark types observed in common minke whales and white-beaked dolphins photographed in Icelandic waters for 11 years (2002–2013) in order to identify reliable markings which could be suitable for capture-mark-recapture studies. In the common minke whale subsample the most prevalent occurring marks were cookie-cutter shark bite, notch and lamprey bite, and herpes-like lesions and blisters were the most abundant. White-beaked dolphins had notch, fin patches and fine scrape as the most prevalent, and black mark and fine scrape were the most abundant. Loss and gain rates were also estimated resulting in eight mark types with no losses in common minke whales including fin outline and injury marks. In white-beaked dolphins there were 13 mark types with null loss rate among which there were notch, distinct notch and amputation. Our findings confirm that fin and injury marks are among the most accurate features to use for capture-mark-recapture studies as noted for other cetacean species. We also suggest including cookie-cutter shark bites for common minke whales and fin patches for white-beaked dolphins due to their low loss rate. These two mark types were amongst the most prevalent in both species, so their addition will be pivotal in increasing the power of analysis conducted using photo-identification data obtaining more accurate population estimates.

Knowledge on the ecology of humpback whales in the eastern North Atlantic is lacking by comparison with most other ocean basins. Humpback whales were historically over-exploited in the region and are still found in low relative abundances. This, coupled with their large range makes them difficult to study. With the aim of informing more effective conservation measures in Ireland, the Irish Whale and Dolphin Group began recording sightings and images suitable for photo-identification of humpback whales from Irish waters in 1999. Validated records submitted by members of the public and data from dedicated surveys were analysed to form a longitudinal study of individually recognizable humpback whales. The distribution, relative abundance and seasonality of humpback whale sighting records are presented, revealing discrete important areas for humpback whales in Irish coastal waters. An annual easterly movement of humpback whales along the southern coast of Ireland is documented, mirroring that of their preferred prey: herring and sprat. Photo-identification images were compared with others collected throughout the North Atlantic (N = 8016), resulting in matches of two individuals between Ireland and Iceland, Norway and the Netherlands but no matches to known breeding grounds (Cape Verde and West Indies). This study demonstrates that combining public records with dedicated survey data is an effective approach to studying low-density, threatened migratory species over temporal and spatial scales that are relevant to conservation and management.

Hybrid cetaceans have been documented to occur both in the wild and in captivity. Identifying wild hybrid individuals can be problematic in the absence of genetic techniques, but published accounts indicate that intermediate morphological characteristics are often present. Between 2010 and 2013, a land-based and boat-based study of the Risso's dolphin (Grampus griseus) was carried out in nearshore waters around the Eye Peninsula located on north-east Lewis, Scotland. Three atypical individuals were photographed which exhibited morphological features intermediate between Grampus and the common bottlenose dolphin (Tursiops truncatus). These individuals were typically larger in body size than Tursiops, and had a dorsal fin shape and size consistent with Grampus. Two individuals had coloration most similar to Tursiops and the third exhibited extensive white linear scarring consistent with Grampus. The intermediate morphology was most apparent in the head shape, with all three individuals exhibiting a defined (in contrast to Grampus) but very short (compared with Tursiops) rostrum and two having an unusually steep (compared with Tursiops) forehead. On one occasion, one of the atypical individuals was observed within a mixed-species school of Grampus and Tursiops. There were four further sightings of atypical dolphins associated with Tursiops-only schools. Atypical dolphins were not recorded within Grampus-only schools. These observations are consistent with hybridization between free-ranging Risso's and bottlenose dolphins, the first such occurrence to be documented for these species in UK waters. The context and significance of these hybridization events are unknown.

Herein, we describe the use of scars to photo-identify the goliath grouper, Epinephelus itajara. Three individuals were photo-identified and re-sighted several times at the same site along the Brazilian coast, including the longest report for site fidelity, with more than four years.

A long-term photo-identification study of killer whales (Orcinus orca) in northern Norway was initiated in 1986, when their prey the Norwegian spring-spawning herring (Clupea harengus) started to winter in a complex fjord system. The aim of this work was to estimate population size and apparent survival rates in this killer whale population using photo-identification and mark–recapture techniques with data collected during October–December 1986–2003. Total population size was estimated to be highest in 2003: 731 individuals (SE = 139, 95% CI = 505–1059) using a model taking heterogeneity of capture probabilities into account. Apparent survival of adult males and adult females was estimated using the Cormack–Jolly–Seber model as 0.971 (SE = 0.008) and 0.977 (SE = 0.009), respectively. Calving intervals ranged from 3 to 14 years (mean = 5.06, SE = 0.722). These are the first estimates of northern Norwegian killer whale population parameters, allowing their dynamics to be investigated and comparisons to be made with killer whale populations globally.

The local population of common bottlenose dolphin in the Balearic Islands coastal waters, a mass tourism destination in the western Mediterranean subject to increasing anthropogenic pressures, was monitored over a three-year period. Photo-identification surveys provided a relatively small population estimate, even though the islands are considered to be a hotspot for the species in the Mediterranean. Dolphins showed strong site-fidelity and relatively limited mobility across the archipelago, which makes them highly dependent on waters which are severely affected by overfishing, habitat degradation and boat disturbance resulting from a continuously-growing tourism and shipping industry. Ecosystem-based management actions are urgently needed to ensure the conservation of this fragile population of bottlenose dolphins. Conservation measures should be developed within the already-existing political and legal marine biodiversity conservation framework and in collaboration with local authorities and stakeholders.

The false killer whale Pseudorca crassidens is currently documented from only six eastern tropical Atlantic (ETA) range states, five of which are evidenced by strandings, by-catch or skeletal remains rather than at-sea sightings and consequently provide no information on habitat or behaviour. Here we report six false killer whale records from cetacean surveys carried out off Gabon (four records) and Côte d'Ivoire (two records) between 2002 and 2012, providing the first at-sea sightings in those two existing range states. All six sightings were located in continental shelf waters (≤103 m depth) and in relatively nearshore (mean = 13.9 km) habitat. Forty-three false killer whales were photo-identified during three encounters on the Gabonese shelf; seven individuals were matched between 2002 and 2006, including two individuals that were present during all three sightings. Observations included predation of Atlantic sailfish Istiophoms albicans and two occurrences in proximity to humpback whales Megaptera novaeangliae. Whistles recorded during one sighting had simple structure, short duration and a mean fundamental frequency of 7.8 kHz. These are the first verified records of false killer whales using continental shelf waters in the ETA, indicating that the species occupies neritic habitat in the region in addition to its previously-documented oceanic habitat. The re-sightings of marked individuals between sightings and years suggest that at least some individuals exhibit a degree of site fidelity to Gabonese shelf waters. Further information on distribution, abundance, movements, population structure and mortality rates are required for effective management of the species in the ETA.

Little is known about the movements of male sperm whales, Physeter macrocephalus, in the North Atlantic. Recoveries of traditional harpoons and tags during commercial whaling indicated movements from Nova Scotia to Spain and from the Azores to Iceland and Spain. We compared collections of photo-identification images from different areas using the North Atlantic and Mediterranean Sperm Whale Catalogue and the Eurphlukes Phlex/Match programs. The largest collections of identified males (number of individuals, start and end date for data collection shown in parentheses) are for the Azores (297, 1987–2008), Andenes (375, 1988–1996 and 2008), Tromsø (84, 2005–2008). There were six matches between Andenes and Tromsø (~25 nm), with three of these re-sighted in multiple years and three photo-identification matches from the Azores to Norway (~2400 nm). In all cases individuals first photographed in the Azores (in 1993, 1999 and 2003) were matched to images collected later in Tromsø (in 2007 and 2008). In 1997 a photo-identification image from Andenes matched a male stranded on the west coast of Ireland. No matches were made to images in smaller collections from Iceland, Nova Scotia, Greenland, Dominica, Guadeloupe, Gulf of Mexico and the Mediterranean. These findings show the value of data collected from whale watching vessels and the importance of collaboration between groups to allow investigation on an ocean basin scale. It is hoped that with the coordinated collection of more images from around the Atlantic, further insight might be gained into the movements of these widely ranging animals.