Larynx strangulation in a resident bottlenose dolphin (Tursiops truncatus) from the Northern Adriatic Sea, Croatia

Probable signature whistle production in Atlantic white‐sided (<i>Lagenorhynchus acutus</i>) and short‐beaked common (<i>Delphinus delphis</i>) dolphins near Cape Cod, Massachusetts

Distribution, and Socioeconomic Analysis of Delphinus delphis and Tursiops truncatus in Relation to Vessel Presence in the Eastern Aegean Sea Objective: This study investigates population abundance and distribution of common (Delphinus delphis) and bottlenose dolphins (Tursiops truncatus) in the Eastern Aegean Sea, where there is limited knowledge of these species. Analyses were made in relation to vessel presence and socioeconomic implications. Methods: Data was collected during boat-based surveys, South of Samos Island and the Northern Dodecanese region, Greece, to determine dolphin population abundance and distribution. Interviews were conducted with native stakeholders to determine socioeconomic factors influencing populations. Results: Mark-recapture photo-identification determined 78 and 76 marked individuals for 2015 and 2017 respectively, for common dolphins, and 31 and zero marked individuals for 2015 and 2017 respectively, for bottlenose dolphins. Common dolphin abundance estimates were 147 in 2015 (95% CL= 109-212) and 180 in 2017 (95% CL= 106-323). For bottlenose dolphins, 2015 estimates were 71 (95% CL= 46-120), while 2017 were unable to be calculated. There was no pattern to either species distribution; however, most sightings occurred near Southern Samos. Considering vessel presence, bottlenose dolphins were sighted most in the presence of fishing vessels, while sightings for common dolphins varied. Bottlenose dolphins showed avoidance of areas where vessels were most present in 2017, compared to 2016, whereas common dolphins did not. Despite competition between artisanal fishermen and populations of these dolphins for the same declining resources, stakeholders had similar awareness for views regarding conservation. Conclusion: Future population fluctuations may occur if vessel traffic continually increases, fishing laws are not abided and enforced, and conservation efforts are not recognized. Additional studies, implementing larger survey areas, are necessary to better understand both species’ population structure and distribution and effects of vessel presence. Moreover, more investigation into socioeconomics, between dolphin conservation and the fishing industry are needed to identify how impactive the industry is to these populations and other cetaceans inhabiting the Eastern Aegean Sea.

Habitat diversity plays a significant role in shaping the genetic structure of cetacean populations. However, the processes involved in defining the genetic differentiation of these highly mobile marine mammals are still largely unknown. Levels of genetic differentiation and dispersal patterns of common bottlenose dolphins (Tursiops truncatus) were assessed in the north‐eastern Mediterranean Sea, with a focus on the Adriatic Sea. This is a region characterized by diverse marine ecosystems and high levels of human‐induced habitat degradation. Although this species seems almost uniformly distributed throughout the Adriatic Basin, genetic evidence rejected the hypothesis of a single stock. Pairwise estimates of genetic differentiation at 12 microsatellite loci, and mitochondrial DNA (entire control region, 920bp), revealed diverse levels of genetic differentiation among five putative populations from the Tyrrhenian Sea to the Aegean Sea. A fine‐scale genetic structure was recorded within the Adriatic Sea, where females appear to be the principal gene flow mediators. The assessment of recent migration rates indicates a relatively high level of gene flow from the North Adriatic towards adjacent areas. Indication of a fine‐scale population structure across the Adriatic Sea is a factor to be carefully considered in the emerging marine management scenario set by the implementation of the EU Marine Strategy Framework Directive (2008/56/CE), particularly when it comes to assessing and managing direct mortality caused by human activities (e.g. fisheries or maritime traffic). A good knowledge of population structure at the basin level is also fundamental for the identification of potential Adriatic Special Areas of Conservation for the bottlenose dolphin under the Habitats Directive (Council Directive 92/43/EEC). Copyright © 2013 John Wiley &amp; Sons, Ltd.

The Adriatic Sea is one of the Mediterranean areas most heavily impacted by fishing and other human stressors. The northern part of the basin has been certified as an Important Marine Mammal Area because of the regular occurrence of common bottlenose dolphins, Tursiops truncatus. Boat surveys, totalling 76 days at sea and 10,711 km of navigation, were conducted between April 2018 and October 2019 to assess cetacean abundance within a 3,000‐km2 area off Veneto, Italy. Bottlenose dolphins – the only marine mammal species observed – were encountered on 52 days and were tracked for 81 h and 26 min, resulting in 15,066 dorsal fin photographs of high quality and resolution. Various capture–recapture models were applied on individual photo‐identification datasets. Model‐based estimates indicate that approximately 600 individuals occurred within the study area during the sampling period in both years. Abundance varied monthly: minimum estimates were obtained in May 2018 (291 individuals; 95% CI 134–630) and May 2019 (121; 95% CI 20–721), whereas maximum estimates were obtained in September 2018 (385; 95% CI 310–477) and October 2019 (494; 95% CI 378–645). Evidence provided by this study can be used to complement and validate coarse ‘snapshot’ information from recent aerial surveys of the entire Adriatic Sea, and to enforce management action mandated by the European Community (EC) Habitats Directive and Marine Strategy Framework Directive, as well as guiding the EC’s Maritime Spatial Planning.

Ammonium urate nephrolithiasis frequently develops in common bottlenose dolphins () managed under human care but is rare in free-ranging common bottlenose dolphins. In other species, the dietary cation-anion difference (DCAD) can affect ammonium urate urolith formation by increasing proton excretion as ammonium ions. Therefore, differences in diet between the 2 dolphin populations could affect urolith formation, but the DCAD of most species consumed by free-ranging and managed dolphins is unknown. To compare the nutrient composition of diets consumed by free-ranging and managed bottlenose dolphins, samples ( = 5) of the 8 species of fish commonly consumed by free-ranging bottlenose dolphins in Sarasota Bay, FL, and the 7 species of fish and squid commonly fed to managed bottlenose dolphins were analyzed for nutrient content. Metabolizable energy was calculated using Atwater factors; the DCAD was calculated using 4 equations commonly used in people and animals that use different absorption coefficients. The nutrient composition of individual species was used to predict the DCAD of 2 model diets typically fed to managed common bottlenose dolphins and a model diet typically consumed by common bottlenose dolphins in Sarasota Bay. To mimic differences in postmortem handling of fish for the 2 populations of bottlenose dolphins, "free-ranging" samples were immediately frozen at -80°C and minimally thawed before analysis, whereas "managed" samples were frozen for 6 to 9 mo at -18°C and completely thawed. "Free-ranging" species contained more Ca and P and less Na and Cl than "managed" fish and squid species. As a consequence, the DCAD of both model managed dolphin diets obtained using 3 of the 4 equations was much more negative than the DCAD of the model free-ranging bottlenose dolphin diet ( < 0.05). The results imply that managed bottlenose dolphins must excrete more protons in urine than free-ranging bottlenose dolphins, which will promote nephrolith formation. The nutrient composition of the free-ranging bottlenose dolphin diet, determined for the first time here, can be used as a guide for feeding managed bottlenose dolphins, but research in vivo is warranted to determine whether adding more cations to the diet will prevent urolith formation in managed dolphins.

Ammonium urate nephrolithiasis frequently develops in common bottlenose dolphins (Tursiops truncatus) managed under human care but is rare in free-ranging common bottlenose dolphins. In other species, the dietary cation–anion difference (DCAD) can affect ammonium urate urolith formation by increasing proton excretion as ammonium ions. Therefore, differences in diet between the 2 dolphin populations could affect urolith formation, but the DCAD of most species consumed by free-ranging and managed dolphins is unknown. To compare the nutrient composition of diets consumed by free-ranging and managed bottlenose dolphins, samples (n = 5) of the 8 species of fish commonly consumed by free-ranging bottlenose dolphins in Sarasota Bay, FL, and the 7 species of fish and squid commonly fed to managed bottlenose dolphins were analyzed for nutrient content. Metabolizable energy was calculated using Atwater factors; the DCAD was calculated using 4 equations commonly used in people and animals that use different absorption coefficients. The nutrient composition of individual species was used to predict the DCAD of 2 model diets typically fed to managed common bottlenose dolphins and a model diet typically consumed by common bottlenose dolphins in Sarasota Bay. To mimic differences in postmortem handling of fish for the 2 populations of bottlenose dolphins, “free-ranging” samples were immediately frozen at −80°C and minimally thawed before analysis, whereas “managed” samples were frozen for 6 to 9 mo at −18°C and completely thawed. “Free-ranging” species contained more Ca and P and less Na and Cl than “managed” fish and squid species. As a consequence, the DCAD of both model managed dolphin diets obtained using 3 of the 4 equations was much more negative than the DCAD of the model free-ranging bottlenose dolphin diet (P < 0.05). The results imply that managed bottlenose dolphins must excrete more protons in urine than free-ranging bottlenose dolphins, which will promote nephrolith formation. The nutrient composition of the free-ranging bottlenose dolphin diet, determined for the first time here, can be used as a guide for feeding managed bottlenose dolphins, but research in vivo is warranted to determine whether adding more cations to the diet will prevent urolith formation in managed dolphins.

Incidental catches of cetaceans in the Dutch pelagic trawl fishery are largely restricted to late-winter early-spring in an area along the continental slope southwest of Ireland. Available evidence indicates that annual variations in such incidents are large. Using combined mid-water trawl by-catch and dolphin stomach content data, the hypothesis is put forward that Atlantic white-sided dolphin (Lagenorhynchus acutus), normally a more oceanic species, may actively search for mackerel (Scomber scombrus) closer to shore in early-spring, at least in some years. Supporting data were from an observer program during 1992–94, which covered seven trips representing 5% of the annual effort in the fishery. Also over the period 1989–94, a total of 71 records of by-catch incidents were collected (involving a minimum of 312 individuals), of which 41 occured in 1994 (172 individuals). Approximately 90% of the incidents occurred late-winter early-spring, when both the mackerel and horse mackerel (Trachurus trachurus) pelagic fisheries were operating in the same area, southwest of Ireland. Incidence frequency peaked by late February and March, when mackerel is known to move into the area during its southward migration. The Atlantic white-sided dolphin was the main cetacean species in the by-catch (83% of all identified individuals). Other species recorded included long-finned pilot whale (Globicephala melas), short-beaked common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus) and the white-beaked dolphin (Lagenorhynchus albirostris). The stomachs of 47 Atlantic white-sided dolphins, 11 common dolphins, two bottlenose dolphins and one white-beaked dolphin were examined. Fresh mackerel remains were found in nearly all white-sided dolphin stomachs, whereas fresh horse mackerel remains occured only in stomachs of bottlenose and common dolphins. Deep-water fish otolith incidents suggested that white-sided, common and bottlenose dolphin had completely different diets before moving to the southwest of Ireland.

The paucity of research into the environmental requirements, stock membership, abundance and residency patterns of bottlenose dolphins (Tursiops truncatus) in coastal Louisiana creates difficulty in understanding how local ecosystems and threats (such as fishery interactions, habitat degradation and pollution) affect populations. This study combined fine-scale environmental measurements and photo-identification techniques to describe patterns of habitat usage and abundance of bottlenose dolphins in lower Barataria Basin from June 1999 to May 2002. In addition I investigated the validity and limitations of using mark-recapture models to estimate abundance from cetacean photo-identification data. Bottlenose dolphins were present year-round in a wide range of water temperatures (10.9 – 33.9 ºC), dissolved oxygen levels (3.7 – 16.6 mg/L), salinities (11.7 – 31.5 psu), turbidity levels (1.4 – 34.0 NTU), distances from shore (3 – 800 m), and water depths (0.4 - 12.5 m). However, feeding activity was concentrated in a narrower range of conditions, 20 – 24 ºC water temperature, 6 – 9 mg/L of dissolved oxygen, turbidity values between 20 – 28 NTU, 200 – 500 m from shore, and depths of 4 – 6 m. Spatial mapping showed differences in the seasonal distribution of individuals and a tendency for feeding activity and larger group sizes to be concentrated in passes. Using distinctive natural markings present on dorsal fins, I identified 133 individual dolphins. Closed-population models were improved by inclusion of temporal and individual heterogeneity as sources of sighting variability and produced estimates of between 138 and 238 (95% CL range = 128 – 297) bottlenose dolphins for the study area. Analysis of Jolly-Seber model assumptions demonstrated the importance of ensuring cetacean surveys accurately represent temporal, geographic and demographic properties of a study population. In addition such factors as non-preferential image acquisition, group size, gender, behavior, stability and distinctiveness of natural markings, weather conditions and boat traffic must be considered. Evidence of a relatively closed Barataria Basin population agrees with current assumptions that bay bottlenose dolphin stocks are distinct from those found in deeper, offshore waters. Furthermore, the characterization of environmental usage patterns for this bay population strengthens adequate description and management of this relatively discrete Gulf of Mexico bottlenose dolphin stock.

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.

The Mediterranean subpopulation of common bottlenose dolphins, Tursiops truncatus, is classified as vulnerable by the IUCN Red list due to its decline in population size by at least 50% within the last 50 years. Identifying the spatial distribution and habitat characteristics of this species is crucial to develop effective conservation and ecosystem management strategies. This research is designed to understand the effect of external parameters on the distribution of bottlenose dolphins off the coast of Montenegro. The northern and central Adriatic Sea have been comparably studied since the 1980s, however the southern Adriatic Sea is suffering from a lack of baseline knowledge. Data collected from boat and land surveys over the past 2+ years was utilized to create a Species Distribution Model (SDM). A random forest model incorporating environmental and physiographic variables to represent the dynamic nature of common bottlenose dolphins is applied. These variables include sea surface temperature (SST), salinity, nutrients (Phosphorus and Nitrogen), bathymetry, slope and distance to coast. The results identified distance to coast, bathymetry, phosphorus and slope as the principal explanatory variables influencing bottlenose dolphin distribution in the southern Adriatic Sea. Bottlenose dolphins were more commonly spotted in shallow waters of &lt;100 m, in areas with a lower degree of slope (0.06 -2.36), with higher phosphorus levels (&gt;0.005 mmol m-3) and between 760 to 2900 m from the coast of Montenegro.

The Mediterranean common dolphin (Delphinus delphis), considered to have been very common in the past, had undergone a dramatic decline across most of the basin by the end of 1970s. In the northern Adriatic Sea, one of the regions with most available historical information, the common dolphin is thought to have been the most common and abundant cetacean throughout most of the 20th century. However, by the end of 1970s, it had virtually disappeared from the region and is now considered generally absent from the entire Adriatic Sea. This contribution summarizes the occurrence of common dolphins in the Gulf of Trieste and provides a brief review of published records in other parts of the Adriatic Sea. Systematic boat surveys in the wider area of the Gulf of Trieste between 2002 and 2019 confirmed that the common bottlenose dolphin (Tursiops truncatus) is the only regularly occurring cetacean species in this area. Despite this, several records of common dolphins were documented in the Gulf of Trieste between 2009 and 2012, through sightings of live animals or recovery of dead stranded animals. Dorsal fin markings allowed the photo‐identification of some of these, suggesting that at least four different live individuals (three adults and one calf) occurred here in recent times. Most cases involved single adult individuals, but one included a mother‐calf pair that was temporarily resident in a port for several months, a behaviour atypical for this species. Photo‐identification showed that the presumed mother had previously been sighted in the Ionian Sea in Greece, over 1,000 km from the Gulf of Trieste, making this the longest documented movement for this species worldwide. At present, the common dolphin continues to be rare in the region.

The main response of top predators to human-induced environmental changes is often behavioral. Although human activities regularly impose a disturbance on top predators, they can also be a source of reliable and concentrated food resources for species with a high degree of behavioral plasticity. This study represents the first assessment of the influence of these resources on migratory patterns and social interaction of a marine top predator, the common bottlenose dolphin, Tursiops truncatus. Pollock’s closed robust design models and association analyses were applied to data collected over 9 consecutive years of research in a coastal area subject to significant use and pressure by humans. Photo-identification data were collected year-round during 955 boat-based surveys, resulting in 1638 common bottlenose dolphin group encounters. Results of this study revealed a significant upward trend in density of bottlenose dolphins, preferences for a coastal area with higher human pressure, and a reduction of the social interactions associated to a temporal switch to the food sources provided by human activities. The observed link between human activities and changes in common bottlenose dolphin behavior aim to contribute to a better understanding of the ecology of a marine top predator and provide some of the needed baseline data, from which effective management and conservation strategies can be designed.

Boat surveys aimed at studying short‐beaked common dolphins and common bottlenose dolphins in eastern Ionian Sea coastal waters were conducted between 1993 and 2003. During 835 survey days, 24 771 km of total effort was distributed within an area of 480 km2, resulting in 428 common dolphin and 235 bottlenose dolphin sightings. Individual photo‐identification was performed extensively throughout this study, making it possible to monitor the number of animals seen in the study area each year and their long‐term residency patterns. Common dolphins declined across the study period, from 2.18 encounters/100 km in 1997 to 0.40 encounters/100 km in 2003. In contrast, there was a relatively stable presence of bottlenose dolphins, some individuals showing high levels of site fidelity and others using the area only occasionally. The local decline of common dolphins and the low density of bottlenose dolphins appeared to reflect the general status of these cetacean species in the wider Mediterranean region, where common dolphins were classified as endangered in the IUCN Red List in 2003. Based on the available evidence, we infer that the present unfavourable status of common dolphins in eastern Ionian Sea coastal waters is largely a consequence of prey depletion. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Understanding marine mammal distributions is essential for conservation, as it can help identify critical habitat where management action can be taken. The semi‐enclosed Gulf of Corinth, Greece, has been identified as an Important Marine Mammal Area by the International Union for Conservation of Nature (IUCN) Marine Mammal Protected Areas Task Force, based on the regular occurrence of odontocete populations. A 7‐year (2011–17) dataset of boat‐based surveys was used to model and predict the distribution of striped dolphins,Stenella coeruleoalba, common dolphins,Delphinus delphis, and common bottlenose dolphins,Tursiops truncatus, in the entire Gulf (2400 km2).Multiple geographic, bathymetric, oceanographic, and anthropogenic variables were incorporated in a combined generalized additive model and generalized estimation equation (GAM‐GEE) framework to describe dolphin occurrence and produce distribution maps.Modelling indicated that striped and common dolphins prefer deep waters (&gt;300 m) in the central and southern part of the Gulf, whereas bottlenose dolphins prefer shallow waters (&lt;300 m) and areas close to fish farms along the northern–central shore.Model‐based maps of the predicted distribution identified a preferred habitat encompassing most of the Gulf, also revealing: (i) hot spots of dolphin distribution covering about 40% of the Gulf's surface; (ii) an almost complete overlap of striped and common dolphin distribution, consistent with the hypothesis that common dolphins modified their habitat preferences to live in mixed species groups with striped dolphins; (iii) a clear partitioning of striped/common and bottlenose dolphin habitat; and (iv) the important role played by fish farms for bottlenose dolphins, consistent with studies conducted elsewhere in Greece.Evidence provided by this study calls for area‐specific and species‐specific management measures to mitigate anthropogenic impacts.

A large‐scale assessment of the summertime suitable habitat for Delphinus delphis (short‐beaked common dolphin) and Tursiops truncatus (common bottlenose dolphin) in Greek Seas (Eastern Mediterranean) was conducted using data from dedicated and opportunistic cetacean surveys and published data records. Using a presence/absence approach, generalized additive models were applied to define a suite of environmental, bathymetric and biotic factors that best describe common and bottlenose dolphin spatial distribution, during early (May, June, July) and late (August, September) summer. A geographic information system (GIS) was used to integrate sightings data with environmental characteristics, distance from the coast and sardine probability of presence. These variables were considered as good proxies for defining species‐suitable habitat within the study area's coastal environment. The final selected models were used to produce annual probability maps of the presence of the species in the entire Greek Seas, as a measure of habitat suitability. Based on the mean probability and standard deviation maps for the study period GIS techniques were subsequently used to determine the persistent (areas with high mean and low variation) and occasional (high mean and high variation) habitat of each species. Results showed that there was a high probability of common dolphin presence in areas with a high probability of sardine presence. For bottlenose dolphin, higher probability of the presence of species occurred in areas closer to the shore, with a high probability of sardine presence and with high concentrations of chlorophyll‐a. In both seasons, the North Aegean Sea and the Inner Ionian Sea Archipelago were indicated as the most suitable areas for common dolphin distribution. Persistent habitat areas of the bottlenose dolphin included enclosed seas, continental shelf waters, and waters surrounding islands. The indicated suitable areas are discussed along with deficiencies of the models and future implications for conservation. Copyright © 2016 John Wiley &amp; Sons, Ltd.