Dolphin Population Research Articles

Seasonal patterns in the mesopelagic fish community and associated deep scattering layers of an enclosed deep basin

Mesopelagic fish constitute the most abundant vertebrate group in the marine environment. The current work reports on results of three seasonal acoustic cruises carried out in the Gulf of Corinth, a relatively small, deep, isolated basin located in the Central Mediterranean (Greece) that presents some unique geomorphological and ecological features. The aim of this study was to describe seasonal echo-types and the vertical distribution of the Deep Scattering Layers (DSLs) as well as to relate them with specific species or species groups. Mesopelagic fish dominated the pelagic ecosystem as confirmed by biological sampling with different gears during daytime and nighttime. In total, at least 15 species were caught, belonging to the families Myctophidae, Paralepididae, Sternoptychidae and Stomiidae, while the—elsewhere very abundant—families Gonostomatidae and Phosichthyidae were completely absent. Common echo-types included: (a) shoals and schools formed by the silvery lightfish Maurolicus muelleri, usually located along the shelf break (80–225 m), (b) a non-migrant thin DSL found at 150–280 m throughout the deep parts of the Gulf, dominated by juvenile half-naked hatchetfish Argyropelecus hemigymnus, and (c) one thick, partially migratory DSL at 250–600 m, mainly consisting of myctophids. The echo backscatter characteristics and species composition of the DSLs as well as the length distribution of the populations were found to differ seasonally. Species-specific and size related patterns in the vertical distribution of fish were detected both during daytime and nighttime. Overall, the Gulf of Corinth seems to sustain high densities of mesopelagic fish that constitute the basic food resource for the abundant dolphin populations that inhabit the area.

Rehabilitation of captive Indo-Pacific bottlenose dolphin (Tursiops aduncus) as a way to combat the effects of climate change

Climate change caused by human industrialization is an unavoidable global problem which started in the 20th century. The high concentration of greenhouse gases has caused global warming, natural disaster, rising sea level, and threatened marine wildlife. It has been proven to decrease the survival rate of dolphins by 12%. This research aims to describe the behavior and assess the readiness to release rehabilitated Tursiops aduncus in Umah Lumba, Banyuwedang Bay, Bali, to boost the wild dolphin population. Visual observation was made on three individuals: Rambo, Rocky and Johnny, at Umah Lumba, Banyuwedang Bay Bali, on March 2021, who have been in the rehabilitation facility since September 2019. The three individuals can be identified by the physical characteristics of their head, mandible, and dorsal fin. The dolphins have developed nine wild-dolphin-like behaviors: respiratory, exploratory, resting, reproductive, social, predatory, spy-hopping, tail-clapping, and sneezing. This rehabilitation program is essential because it increases the population of wild dolphins by acclimating, adapting, and training former captive dolphins for release.

Areas of spatial overlap between common bottlenose dolphin, recreational boating, and small-scale fishery: management insights from modelling exercises.

Sustainable management requires spatial mapping of both species distribution and human activities to identify potential risk of conflict. The common bottlenose dolphin (Tursiops truncatus) is a priority species of the European Union Habitat Directive, thus, to promote its conservation, the understanding of habitat use and distribution, as well as the identification and spatial trend of the human activities which may directly affect populations traits, is pivotal. A MaxEnt modeling approach was applied to predict the seasonal (from April to September) habitat use of a small population of bottlenose dolphins in the north-western Sardinia (Mediterranean Sea) in relation to environmental variables and the likelihoods of boat and fishing net presence. Then, the overlapping areas between dolphin, fishing net and boat presence were identified to provide insights for the marine spatial management of this area. Three of the main factors influencing the seasonal distribution of bottlenose dolphins in the area are directly (boating and fishing) or indirectly (ocean warming) related to human activities. Furthermore, almost half of the most suitable area for dolphins overlapped with areas used by fishing and boating. Finally, relying on fishing distribution models, we also shed light on the potential impact of fishing on the Posidonia oceanica beds, a protected habitat, which received higher fishing efforts than other habitat types. Modelling the spatial patterns of anthropogenic activities was fundamental to understand the ecological impacts both on cetacean habitat use and protected habitats. A greater research effort is suggested to detect potential changes in dolphin habitat suitability, also in relation to ocean warming, to assess dolphin bycatch and the status of target fish species, and to evaluate sensitive habitats conditions, such as the Posidonia oceanica meadow.

Assessing spatial patterns and density of a dolphin population through signature whistles

AbstractSome dolphin species produce signature whistles, which may allow the identification of individual dolphins using passive acoustic monitoring (PAM). Identifying individuals by their sounds may enhance the opportunities for monitoring and addressing biological and ecological questions about these species. Here, we explored the potential of signature whistles to investigate ecological aspects of a resident bottlenose dolphin population. Using a limited data set, with few individuals recognized by signature whistles, combined with spatial capture‐recapture (SCR) methods, we investigated how effective such approach is describing spatial use patterns and estimating density for this population. The data were collected using 4–6 stationary bottom‐moored recorders. Since only eight signature whistles were identified, our density estimate may represent a subset of the entire population. However, even with only a few signature whistles identified, our results confirmed the center of the core area used by these dolphins as the area with the highest encounter probability. In addition, our results provided evidence that these dolphins have the same spatial use pattern at night as during the day. This study shows that SCR analysis of signature whistle data can improve our ecological knowledge and understanding of dolphin populations.

Short-beaked common dolphins of Dilek Peninsula National Park, South Aegean Sea: Preliminary results on group structure, spatial distribution, behavioural patterns, whistle characteristics and behavioural context

Basic knowledge about populations of short‐beaked common dolphins (Delphinus delphis) in the eastern part of the Mediterranean Sea is still lacking. Classified as ‘Endangered’ in an IUCN assessment released in 2022, it is necessary to gain baseline knowledge to understand the species’ population status and develop impactful conservation measures. The current study conducted boat surveys, employing visual and acoustic techniques between January 2019 and July 2022 in the Dilek Peninsula National Park, central Aegean Sea. Results revealed the continuous coastal presence of common dolphins, with subadults recorded during every sighting in low group sizes. Travelling‐related activities made up 58% of observed behaviour while resting comprised just 1%. Whistles were produced in the range of 1.83–48kHz with a peak frequency of 10.4kHz and median duration of 0.54s. Concave whistles were the most frequently recorded whistle type. Whistles were found to be generated when dolphins were interacting with boats and diving/travelling fast, forming 53% and 31% of whistle production respectively. The continuous presence of common dolphins, particularly subadults, emphasises the importance of the Dilek Peninsula. Whistle parameters show similarities with other common dolphin populations of the Mediterranean and Black Sea, albeit with shorter durations. The high whistle presence during boat interactions requires investigation to assess whether whistles carry avoidance or predatory messages, or whether there are potential consequences for the species’ energy budget. The current study presents preliminary information on the behavioural context of acoustic patterns. Further research is essential to understand the click and whistle characteristics within the biological, environmental and anthropogenic variables of their surroundings.

Using ecotourism boats for estimating the abundance of a bottlenose dolphin population in south-eastern Australia.

It is challenging to collect robust, long-term datasets to properly monitor the viability and social structure of large, long-lived animals, especially marine mammals. The present study used a unique long-term dataset to investigate the population parameters and social structure of a poorly studied population of bottlenose dolphins (Tursiops sp.) in southern Port Phillip Bay, south-eastern Australia. Photo-identification images have been collected between 2012-2022 both opportunistically and following a protocol by patrons, staff, and volunteers of ecotourism companies using their vessels as platforms. The resulting large dataset was available to be processed through the online platform Flukebook and used in capture recapture models to estimate abundance and demographic parameters. In addition, the social structure of the population and the reproductive parameters were investigated. The marked adult population abundance (45.2 ± 2.7 individuals) was found to be stable over the last decade and the calving rate ranged between 0.06-0.19 new calves per identified individuals per year, while the inter-birth interval was 3.7 ± 0.8 years. Social analysis suggested the population has a fission-fusion structure with no apparent clusters. The stability of the population over the study period suggests no deleterious effect of anthropogenic or environmental factors during the last decade. This study is the outcome of the effort of the ecotourism organisations and the results obtained, along with their similarity to those of other dolphin populations worldwide, highlight the importance of such data sources for long-term information that would otherwise be too expensive or logistically difficult to obtain.

20 years of research on the Guiana dolphin population of Sepetiba Bay, southeastern Brazil: What has changed?

Abstract Despite the importance of coastal habitats for the provision of many ecosystem services, these areas are currently among the most impacted by human activities. Impacts on coastal ecosystems may affect many key species, such as the Guiana dolphin, which inhabits Sepetiba Bay in south‐eastern Brazil, a highly degraded environment owing to a human‐induced rapid environmental change. In this context, this study investigates the potential changes in the local Guiana dolphin behaviour, group structure, bioacoustics, site fidelity and habitat use over the past 20 years. For this, a historical database (1998–2007) was compared with current data on the local dolphin population (2017–2019). Between 2017 and 2019, the Guiana dolphins form significantly smaller groups (W = 3262.5, P > 0.001), spend more time foraging (61 vs. 10% in the past), emit whistles at a considerably lower rate (decreasing by 85.2%), have reduced site fidelity and now use a larger area. As Sepetiba Bay has been severely impacted by human activities in the recent past, with profound consequences for much of its biodiversity, the observed changes in dolphin behaviour are probably a consequence of habitat degradation and, in particular, of reduced prey availability. These findings have important implications for the management and conservation of the Guiana dolphin population of Sepetiba Bay. To break this human‐induced rapid environmental change, it will be essential to minimize the spatio‐temporal overlap of anthropogenic impacts, to avoid cumulative impacts. To mitigate anthropogenic impacts on the Guiana dolphins of Sepetiba Bay, it will be important to direct the following actions: (i) the regulation and control of anthropogenic noise; (ii) reduction and control of the release of chemical contaminants and organic effluents; (iii) more effective controls on vessel traffic within the areas used preferentially by the Guiana dolphin; and (iv) the implementation of measures to avoid overfishing and bycatch.

The fitness consequences of human‐wildlife interactions on foraging common bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida

AbstractHuman‐wildlife interactions (HI) are becoming more prevalent with increasing human population. These interactions could have important eco‐evolutionary consequences that become apparent only after observing populations for multiple generations. Here, we analyzed 28 years (1993–2020) of data from the world's longest‐running study of a wild dolphin population to assess the fitness consequences of HI on common bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida. We investigated how human‐related foraging activities such as depredation, begging, and patrolling mediate reproductive output and reproductive success of conditioned (HI) and unconditioned (non‐HI) females. The analysis of 84 females and their 286 calves born during 1993–2020 found a confluence of effects on individual fitness. Reproductive output of females engaging in moderate levels of human‐related foraging was 94% greater than that of non‐HI females. However, high frequencies of human‐related foraging had a negative effect on female reproductive success by increasing the risk of calf death up to nine times when compared to non‐HI females, resulting in 31% less calf survival. These findings provide evidence that human‐wildlife interactions have considerable potential to catalyze population‐level changes by altering individual fitness, and demonstrate the value of comprehensive, long‐term data to better understand the ecological and evolutionary implications of human‐wildlife conflict.

Abundance of the bottlenose dolphin (Tursiops truncatus) and proposal for a priority area of conservation in the Southern Gulf of Mexico marine ecoregion

Abstract Demographic studies are crucial for assessment of the status of dolphin populations and their relationship with anthropogenic activities as a way to make effective management and conservation decisions. In the Gulf of Mexico, the interaction between bottlenose dolphins (Tursiops truncatus) and anthropogenic activities merits special attention. The objective of this study was therefore to determine the annual abundance and area of preference of the coastal population of T. truncatus (period 2005–2020), and to delimit a priority area for its conservation in the Southern Gulf of Mexico marine ecoregion. Abundance was calculated using the Jolly–Seber model and habitat preference was determined per climatic season (dry, rainy and cold northerly fronts) as a function of environmental variables. The association between anthropogenic activities and dolphin distribution was studied and the priority area delimited using potential distribution models. Off the coasts of Tuxpan and Tamiahua, the results show that the dolphin population numbered 306 individuals (95% CI: 162.97; 607.33) and has remained relatively constant over time. The pattern of dolphin distribution varied between seasons, possibly owing to changes in food availability. However, river mouths and lagoons are of importance to T. truncatus throughout the year. On the other hand, fishing and maritime traffic can potentially affect this species. Finally, this study shows that the delimitation of sites of importance for T. truncatus is a strategic tool with which to help conserve the species and associated coastal ecosystems.

Stable isotope ecology and interspecific dietary overlap among dolphins in the Northeast Atlantic

Dolphins are mobile apex marine predators. Over the past three decades, warm-water adapted dolphin species (short-beaked common and striped) have expanded their ranges northward and become increasingly abundant in British waters. Meanwhile, cold-water adapted dolphins (white-beaked and Atlantic white-sided) abundance trends are decreasing, with evidence of the distribution of white-beaked dolphins shifting from southern to northern British waters. These trends are particularly evident in Scottish waters and ocean warming may be a contributing factor. This mobility increases the likelihood of interspecific dietary overlap for prey among dolphin species previously separated by latitude and thermal gradients. Foraging success is critical to both individual animal health and overall population resilience. However, the degree of dietary overlap and plasticity among these species in the Northeast Atlantic is unknown. Here, we characterise recent (2015-2021) interspecific isotopic niche and niche overlap among six small and medium-sized delphinid species co-occurring in Scottish waters, using skin stable isotope composition (δ13C and δ15N), combined with stomach content records and prey δ13C and δ15N compiled from the literature. Cold-water adapted white-beaked dolphin have a smaller core isotopic niche and lower dietary plasticity than the generalist short-beaked common dolphin. Striped dolphin isotopic niche displayed no interspecific overlap, however short-beaked common dolphin isotopic niche overlapped with white-beaked dolphin by 30% and Atlantic white-sided dolphin by 7%. Increasing abundance of short-beaked common dolphin in British waters could create competition for cold-water adapted dolphin species as a significant portion of their diets comprise the same size Gadiformes and high energy density pelagic schooling fish. These priority prey species are also a valuable component of the local and global fishing industry. Competition for prey from both ecological and anthropogenic sources should be considered when assessing cumulative stressors acting on cold-water adapted dolphin populations with projected decline in available habitat as ocean temperatures continue to rise.

Entanglement in recreational fishing gear poses a threat to estuarine and coastal dolphins: Animal welfare and population level impacts should guide intervention decision making

Derelict and active fishing gear poses a threat to marine wildlife. This study details Indo-Pacific bottlenose dolphin entanglements in recreational fishing gear in the Peel-Harvey Estuary, Western Australia between 2016 and 2022. Eight entanglements were recorded, three resulted in death. While concerning from an animal welfare perspective, the impact of entanglements on the viability of the local dolphin population was low. This is as majority of affected individuals were juvenile males. Should entanglements result in the loss of reproductive females, or impact their reproductive success, the population trajectory could quickly change. As such, management decision making should consider population level impacts as well as the welfare of entangled individuals. Government agencies, together with relevant stakeholders, should work together to maintain preparedness to respond to entanglements and take preventative action that lowers the risk of interactions with recreational fishing gear.

Variation in foraging activity influences area-restricted search behaviour by bottlenose dolphins.

Area-restricted search (ARS) behaviour is commonly used to characterize spatio-temporal variation in foraging activity of predators, but evidence of the drivers underlying this behaviour in marine systems is sparse. Advances in underwater sound recording techniques and automated processing of acoustic data now provide opportunities to investigate these questions where species use different vocalizations when encountering prey. Here, we used passive acoustics to investigate drivers of ARS behaviour in a population of dolphins and determined if residency in key foraging areas increased following encounters with prey. Analyses were based on two independent proxies of foraging: echolocation buzzes (widely used as foraging proxies) and bray calls (vocalizations linked to salmon predation attempts). Echolocation buzzes were extracted from echolocation data loggers and bray calls from broadband recordings by a convolutional neural network. We found a strong positive relationship between the duration of encounters and the frequency of both foraging proxies, supporting the theory that bottlenose dolphins engage in ARS behaviour in response to higher prey encounter rates. This study provides empirical evidence for one driver of ARS behaviour and demonstrates the potential for applying passive acoustic monitoring in combination with deep learning-based techniques to investigate the behaviour of vocal animals.

Dolphin interactions with tuna feedlots at Port Lincoln, South Australia and recommendations for minimising entanglements

Cetacean carcasses near Port Lincoln and entanglements in southern blue-fin tuna feedlots were monitored between 1990 and 1999. Dolphins became entangled and died in large-mesh (usually > 15cm) anti-predator nets around the cages, from surface to seafloor (18m). The carcasses were retrieved and studied with respect to diet and life history. During the period of study, 29 dolphins (15 bottlenose, 9 common, 5 unidentified) were confirmed entanglement deaths and an additional eight unconfirmed reports of dead dolphins were made between 1993 and 1996. Beach-washed or floating carcasses of an additional 38 dolphins were found in the Port Lincoln region during 1990-1999, four of which were suspected entanglements. The carcasses of 23 entangled and four suspected entangled dolphins were studied for diet, and reproductive and relative age characteristics. At least 24 of the 33 entangled animals were juveniles or sexually mature animals, of which most of the females were pregnant or lactating. Three calves and no neonates were entangled. Gastrointestinal contents of 57 bottlenose and common dolphins from elsewhere along the coast of South Australia were also studied. Cephalopods were more abundant in bottlenose dolphins than common dolphins, including those entangled in tuna feedlots. Carangidae were the main identified fish prey of dolphins entangled in tuna nets. The study concluded that dolphins were being attracted to, and feeding in, the area of the cages. Recommendations for minimising entanglements include removing anti-predator nets or reducing mesh size to less than 8cm, reducing tuna food wastes and thereby the food source for other fish in the vicinity, and rigorous monitoring of both entanglements and dolphin populations in the Port Lincoln region.

Submarine canyons as key habitats to preserve Risso’s dolphin (Grampus griseus) populations in the northwestern Mediterranean Sea

This paper summarises the occurrence of Risso’s dolphin (Grampus griseus) over 12 years (2009 to 2021) in the northwestern Mediterranean. The study was conducted off the central coast of Catalonia (NE Spain) in an area covering 8,026 km2 and featuring a system of submarine canyons. The habitat is suitable for a wide diversity of species, including deep-diving cetaceans. In addition, a different dataset from other projects was included to compare distances to the coast from different periods. A visual effort of 8,756 km was carried out with the recording of 17 Risso’s dolphin sightings. The relative mean density of Risso’s dolphin was 0.0078 individuals/km2 (SD 0.1, n = 17), and the densities were higher in the southern canyons than in the northern canyons. Furthermore, the distance to the coast and the depth of any sighting were compared by gathering data from different periods and surveys (first period 1985–2014; second period 2016–2021) with 34 sightings analysed. Significant differences were found related to the distance to the coast, showing a displacement of the animals to more pelagic areas between periods. The spatial distribution of Risso’s dolphins was investigated by applying a generalized additive model based on sighting data collected during standardized vessel surveys. Four predictive variables were considered, taking into account the local physiographical features. The model showed that the spatial distribution of Risso’s dolphin in the area was related to the slope and slope variation. The species showed preferences for offshore areas as significant differences were obtained in terms of the distance of sightings to the coast. This paper provides new insights into the distribution of Risso’s dolphin in the central western Mediterranean Sea and identifies the submarine canyons of northern Catalonia as an essential habitat for the species.

To be or not to be controlled? The ecological role of the Guiana dolphin in its southernmost range

Several studies have explored dolphins feeding ecology in coastal ecosystems; However, research gauging the predatory effects of delphinid on ecosystems, which can be applied to management and conservation efforts, is still lacking. The northwestern section of the bay of Santa Catarina Island, locally known as North Bay, in Southern Brazil, inhabits the southernmost population of the Guiana dolphin (Sotalia guianensis). This small and resident population is structured in a single and highly cohesive group, using a small home range restricted to the western section of the bay. Like many other coastal dolphins, this dolphin population negatively interacts with fisheries, with frequent bycatch events or by sharing feeding resources. To explore the ecological role of dolphins in the North Bay ecosystem, we constructed an Ecopath food web model to estimate ecosystem and compartmental attributes. Mixed trophic impact and keystoneness index were used to assess the predatory effects of the species in the ecosystem. As a complementary approach to Ecopath, we used ecological network analysis (ENA) to determine the ecological role of the compartments using control analysis and the throughflow centrality. According to our model, North Bay is a mature detritus-based ecosystem. Dolphins showed the highest keystoneness index score among all functional groups, while control analysis showed they are also the most controlled component in the ecosystem. The dolphins rely mainly on the Whitemouth croaker (Micropogonias furnieri), a hub species showing the greatest centrality of flows. We concluded that the Guiana dolphin inhabiting the North Bay is a crucial compartment in the ecosystem. It shows the greatest ecosystem impact per biomass unit among all functional groups, while it is the most vulnerable compartment.

The effect of physiographic and hydrologic complexities and their alterations on the distribution of obligate freshwater dolphins.

Physiographic and hydrologic complexities play major role in determining the habitat suitability for river dolphins. However, dams and other water development structures alter hydrologic regimes that degrade habitat conditions. For the three extant species of obligate freshwater dolphins, namely: Amazon dolphin (Inia geoffrensis), Ganges dolphin (Platanista gangetica), and Indus dolphin (Platanista minor), the threat is high as dams and water-based infrastructure dotted throughout their distribution range impact dolphin populations by restricting their movement. But there is also evidence of localized increase in dolphin population in certain segments of habitats affected by such hydrologic alterations. Hence, the impacts of hydrologic alterations on dolphin distribution are not as binary as it seems. We aimed to ascertain the role of hydrologic and physiographic complexities in determining the distribution of the dolphins in their geographic ranges using density plot analysis and also to understand how hydrologic alterations in the rivers affect their distribution using a combination of density plot analysis and review of literature. The influence of some of the study variables such as distance to confluence and sinuosity was similar across species-for instance, all three dolphin species preferred slightly sinuous river segments and habitats near confluences. However, varying influences across species were observed for some other variables such as river order and river discharge. We assessed 147 cases of impacts of hydrological alterations on dolphin distribution by categorizing the reported impacts in nine broad types out of which habitat fragmentation accounted for the majority of the impacts (35%) followed by habitat reduction (24%). These endangered species of freshwater megafauna will experience further intensified pressures as more large-scale hydrologic modifications such as damming and diversion of rivers are underway. In this context, basin-scale water-based infrastructural development planning should take into consideration the salient ecological requirements of these species to ensure their long-term survival.

The role of skin biopsy in the detection of exposure to endocrine disrupting chemicals in Mediterranean cetaceans

Use of skin biopsy is proposed as a sensitive non-lethal technique for the hazard assessment of Mediterranean cetaceans exposed to endocrine disrupting chemicals (EDCs). EDCs are a structurally diverse group of compounds that may adversely affect the health of humans and wildlife or their progeny, by interaction with the endocrine system. In the Mediterranean environment top predators accumulate high concentrations of polyhalogenated aromatic hydrocarbons (PHAHs) and toxic metals, incurring high toxicological hazard. In this paper, the hypothesis that Mediterranean cetaceans are potentially at risk due to PHAH-EDCs is investigated using skin biopsy samples. Benzo-a-pyrene monoxigenase (BPMO) activity in skin biopsies was used as a potential indicator of exposure to different organochlorines (OCs) known to have endocrine disrupting properties. The main objective of this paper was to use this non-destructive ecotoxicological tool to define the potential hazard to Mediterranean odontocete and mysicete species, comparing the present data with values detected in other cetaceans from heavily polluted areas, affected by pseudohermaphroditism and other reproductive dysfunction. Subcutaneous tissue consisting of skin and blubber was obtained from striped dolphins (Stenella coeruleoalba), bottlenose dolphins (Tursiops truncatus), common dolphins (Delphinus delphis) and fin whales (Balaenoptera physalus) in the Mediterranean basin. Sampling was performed in the western Ligurian Sea, between Corsica and the French-Italian coast, and in the Ionian Sea. High concentrations of DDT metabolites and PCB congeners (known as Endocrine Disruptors) were detected in the different species. Significant differences in BPMO induction and OC levels were found between odontocetes and mysticetes. Differences in organochlorine bioaccumulation and consequently potential risk due to endocrine disruptors were primarily related to different positions in the marine food web. A statistical correlation was found between BPMO activity and organochlorine (op’DDT, a potent estrogen and antiandrogen and pp’DDE, a potent antiandrogen) levels in skin biopsy specimens of the endangered Mediterranean population of common dolphin. Several conclusions on the potential risk to Mediterranean cetaceans can be drawn from comparison of the levels of OC-EDs detected in Mediterranean odontocetes with those in white whales (Delphinapterus leucas) of the St Lawrence estuary and bowhead whales (Balaena mysticetus) affected by pseudohermaphroditism and other reproductive dysfunction. Finally, these results suggest that BPMO induction may be an early sign of exposure to EDCs such as OCs and a warning of the possibility of transgenerational effects through exposure of future generations via the placenta and milk.

Distribution of small cetaceans within a candidate Special Area of Conservation; implications for management

Information on cetacean distribution plays an important role in the identification of suitable boundaries for marine protected areas, but is also crucial for developing management and monitoring programmes. In response to the European ‘Habitats Directive’, a candidate Special Area of Conservation (cSAC) has been established in the Moray Firth, northeast Scotland to protect a small and isolated population of common bottlenose dolphins (Tursiops truncatus). Limited data on the distribution of bottlenose dolphins and on temporal changes in distribution have recently constrained attempts to mitigate against the impacts of new developments upon this population. In response to the need for current information on the distribution of dolphins throughout the cSAC, this study aims to provide data on the distribution of dolphins and other small cetaceans throughout the Moray Firth. Changes in the distribution patterns of dolphins in the inner Moray Firth were examined using data collected between 1990 and 2000. In addition, combined passive acoustic and visual survey techniques were used to determine the distribution of dolphins and harbour porpoises (Phocoena phocoena) on a broader scale across the whole Moray Firth. Dolphin schools were distributed throughout the inner Moray Firth, but there were concentrations of sightings around three deep, narrow channels that were consistent over the ten year study period. Results from surveys across the whole of the Moray Firth showed that all sightings and acoustic detections of dolphins were made within the area of the cSAC. In contrast, porpoise sightings were widely distributed throughout the Moray Firth. The median encounter rate of porpoises across the whole Moray Firth was 1.69 per 100km. Encounter rates of porpoises were similar in the outer Moray Firth and the cSAC. This combination of distribution studies at differing spatial scales provides a valuable tool for monitoring the distribution of animals and identifying important habitats, and the results of this study have directly supported efforts to manage the cSAC.

An expert-based system to predict population survival rate from health data.

Timely detection and understanding of causes for population decline are essential for effective wildlife management and conservation. Assessing trends in population size has been the standard approach, but we propose that monitoring population health could prove more effective. We collated data from 7 bottlenose dolphin (Tursiops truncatus) populations in the southeastern United States to develop a method for estimating survival probability based on a suite of health measures identified by experts as indices for inflammatory, metabolic, pulmonary, and neuroendocrine systems. We used logistic regression to implement the veterinary expert system for outcome prediction (VESOP) within a Bayesian analysis framework. We fitted parameters with records from 5 of the sites that had a robust network of responders to marine mammal strandings and frequent photographic identification surveys that documented definitive survival outcomes. We also conducted capture-mark-recapture (CMR) analyses of photographic identification data to obtain separate estimates of population survival rates for comparison with VESOP survival estimates. The VESOP analyses showed that multiple measures of health, particularly markers of inflammation, were predictive of 1- and 2-year individual survival. The highest mortality risk 1year following health assessment related to low alkaline phosphatase (odds ratio [OR]=10.2 [95% CI: 3.41-26.8]), whereas 2-year mortality was most influenced by elevated globulin (OR=9.60 [95% CI: 3.88-22.4]); both are markers of inflammation. The VESOP model predicted population-level survival rates that correlated with estimated survival rates from CMR analyses for the same populations (1-year Pearson's r=0.99, p=1.52×10-5 ; 2-year r=0.94, p=0.001). Although our proposed approach will not detect acute mortality threats that are largely independent of animal health, such as harmful algal blooms, it can be used to detect chronic health conditions that increase mortality risk. Random sampling of the population is important and advancement in remote sampling methods could facilitate more random selection of subjects, obtainment of larger sample sizes, and extension of the approach to other wildlife species.

Better or worse food: Nutrition value of the prey fishes and the potential health implications for Indo-Pacific humpback dolphins

IntroductionOverfishing and climate change have combined to cause fishery stocks to decline and fish community composition to change, further threatening the predation and nutritional health of marine mammals.MethodsIn this study, we collected potential prey fishes catched by fishermen in six habitats of Indo-Pacific humpback dolphins and analyzed their proximate composition (moisture, water, fat and protein), the fatty acid composition and the amino acid composition to evaluate the possible health effect on humpback dolphins.ResultsThe results showed that the nutritional composition varied significantly with species and locations. Fishes in the families Sciaenidae and Engraulidae displayed richer fatty acid composition, while those in the family Clupeidae had the highest value of amino acid quality index. In Zhuhai, home to the largest Indo-Pacific humpback dolphin population, pelagic/neritic prey fishes possessed lower energy density, PUFA content, PUFA/SFA ratio, DHA content, and EAA content compared to demersal fish, suggesting nutritional stress when there is a dietary switch from demersal to pelagic/neritic fishes in Zhuhai population.DiscussionOur study provided a framework, with energy density and fatty acid composition as its most important indicator, for assessment of the marine top predators based on the nutritional composition of their prey fishes and revealed the potential threats. Data here is expected to facilitate the development of scientific programs for successful conservation of not only the Indo-Pacific humpback dolphins, but also other marine top predators, possibly through reconstructing their prey fish’s quantity and quality.