The field of welfare science and public concern for animal welfare is growing, with the focus broadening from animals on farms to those in zoos and aquaria. Bottlenose dolphins (Tursiops truncatus) are the most common captive cetaceans, and relevant regulatory standards are principally resource-based and regarded as minimum requirements. In this study, the farm animal Welfare Quality® assessment was adapted to measure the welfare of bottlenose dolphins, with a similar proportion of animal-based measures (58.3%). The ‘C-Well® ‘ assessment included eleven criterion and 36 species-specific measures developed in situ at three marine mammal zoological facilities, tested for feasibility and accuracy, and substantiated by published literature on wild and captive dolphins and veterinary and professional expertise. C-Well® scores can be calculated for each measure or combined to achieve an overall score, which allows for the comparison of welfare among individuals, demographics, and facilities. This work represents a first step in quantifying and systematically measuring welfare among captive cetaceans and can be used as a model for future development in zoos and aquaria, as well as a means to support benchmarking, industry best practices, and certification.

Animal welfare science is a burgeoning field, but research on cetaceans (whales, dolphins and porpoises) is lacking. Bottlenose dolphins (Tursiops truncatus) are the most well-known and studied cetaceans, particularly in captivity, and thus are used in this review as a model for other cetacean species. Despite the public interest and need for such research, studies specifically investigating dolphin welfare are lacking. This review uses the three broad categories of behaviour, health, and cognition, to discuss how dolphin welfare has been assessed thus far, and could be assessed in future. We present welfare indicators validated in other species that could be applied to dolphins, including innovative measures, such as cognitive appraisal of emotions. We provide a summary of practical recommendations for validating the indicators of bottlenose dolphin welfare. This paper aims to stimulate further research into dolphin welfare which could improve the lives of the animals themselves and ultimately support regulatory decisions. We recommend uniting expertise in cetology and welfare science in order to develop a holistic approach to dolphin welfare assessment.

Fisheries constitute a major threat to marine mammals globally. To evaluate the impact of small-scale fisheries (SSF) on regional under-studied marine mammal populations, we tested a novel and cost-effective approach at three data-limited locations of the central and eastern Mediterranean Sea. Using off-the-shelf GPS loggers to track SSF activities and systematic surveys to map the distribution of marine mammals, we assessed the probability of co-occurrence between SSF and marine mammals by reporting areas of spatial overlap. Spatial overlap between SSF and the core zones of marine mammal distribution (ranging between 21.85–35.4%) was observed in all three locations, indicating potential interaction hotspots. The probability of co-occurrence in those areas varied from 0.5–2.9% depending on the species. The resulting overlap between fishing activity and marine mammals may pose a threat in both directions: higher risk of species entanglement and economic burden on fishers due to gear damage. Despite the spatial and temporal limitations of this pilot study, the proposed approach can provide baseline information on SSF-marine mammal co-occurrence, particularly in financially limited regions. If applied on a larger scale, our method may be used to inform future conservation actions with the aim to reduce pressure on key populations.

The Istanbul Strait is an important cetacean habitat that is intensely used by humans. Yet little is known about their spatial-temporal distribution. To understand the encounter rates and residency patterns of bottlenose dolphins, photo-identification data were collected between 2011 and 2016 in the Istanbul Strait. The study showed that bottlenose dolphins are a regular, year-round component of the strait. The encounter rate was estimated to be four groups (22 individuals) per 10 km. The adjacent waters of Marmara Sea and Black Sea, that host relatively less marine traffic, had the highest number of encounters in the area. Conversely, the middle sections had the lowest number of encounters but the highest marine vessel density. Further, the encounter rates dropped to zero in the fishing zones, where the number of purse seines reached up to 100 per day. Additionally, dolphins showed varying degrees of residency patterns, with multi-year re-sightings. Maximum re-sighting distance was up to 35 km, which is more than the total length of the strait. This movement pattern should be investigated as it might reveal possible migration between local populations. This study finds that the Istanbul Strait serves as a critical habitat for the regional bottlenose dolphin populations and they are likely to be a part of a resident local population with a home range extending the length of the strait. Dedicated surveys with inter-regional collaborations are needed to evaluate the home range and population status of this endangered species for their effective conservation in one of the busiest waterways of the world.

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.

The management scheme of Marine Protected Areas (MPAs) includes monitoring protocols but such activities are not always carried out. This is the case for Golfo San José, a MPA in northern Patagonia, Argentina. It was created in 1975 for the protection of the southern right whale (Eubalaena australis) breeding grounds. Other components of the system, such as dolphin populations have received little attention. This study is the first attempt to estimate sighting rates, group size and overall abundance of a bottlenose dolphin (Tursiops truncatus) population in Golfo San José and adjacent areas after 30 years. An analysis of the seasonal sighting rates indicates that bottlenose dolphins were present in the study area throughout the year but a decline in group size and abundance and major shift in distribution was detected when compared with previous published reports. The settlement of the MPA failed to secure the persistence of the bottlenose dolphin population within its boundaries. Possible explanations for the detected decline are addressed including increased natural mortality, human induced mortality and disturbance, resources depletion and environmental shift.

The resident population of common bottlenose dolphins (Tursiops truncatus) in the Sado Estuary, Portugal, has been declining at least during the past three decades. A complete photographic census produced a current count of 24 animals—19 adults, three subadults and two calves. It appears to be phylopatric and essentially closed, but given the likely importance that exchanges with neighbouring coastal groups may play, even if rare, the most adequate term to define this dolphin should be community and not population. Large groups with all age-classes are common in the community, possibly as a calf and subadult protection strategy, and this may be related to the fact that these age-classes have had high mortality rates in the last decade. Maternity of two calves was determined, and we found that the two mothers adopted different parenting strategies. While one mother spent more time alone with her calf, the other mother spent more time with her calf in larger groups. The average coefficient of association for this community is 0.45, quite high for this species. Associations and typical group size are similar between all individuals, with no patterning according to age-class or sex, which constitutes an atypical trait for dolphin societies. There are also no clear divisions in this community according to cluster analysis. Associations are preferred and long term, lasting approximately 34 days and fitting a pattern of casual acquaintances, where individuals associate for a period of time, disassociate and may reassociate after that. This reflects the fission–fusion character of the community, but in a more stable manner. We think this is caused by a combination of demographic characteristics and a stable and productive environment, which led to a decrease in competition between individuals.

Reliable methods to identify and monitor cetacean individuals are important to assess population behaviour and ecology. We describe and evaluate the application of the digital video-identification technique (DVI) for the acquisition and analysis of dorsal fin images in the study of bottlenose dolphins (Tursiops truncatus) in the Cagarras Archipelago, Rio de Janeiro, Brazil. Between August and November 2004, we identified and catalogued 20 individuals; 80% were re-sighted more than twice. The Individual Residence Index varied between 1.0 (N = 1) and 0.2 (N = 4). Compared with traditional photo-identification methods, DVI offers significant advantages in respect to production of sequential images and speed of editing and processing.