The North Sea is an ecologically rich habitat for marine wildlife which has also been impacted by industrial developments and anthropogenic emissions of contaminants such as mercury. Marine mammals ...are particularly susceptible to mercury exposure, due to their trophic position, long lifespan, and dependence on (increasingly contaminated) aquatic prey species. To mitigate impact, marine mammals can detoxify methylmercury by binding it to selenium-containing biomolecules, creating insoluble mercury selenide granules. Here, liver, kidney, muscle, and brain samples from an adult male bottlenose dolphin (Tursiops truncatus) with known elevated mercury concentrations were analysed through scanning electron microscopy (SEM). Tiemannite (HgSe) deposits were identified in all organs, ranging from 400 nm to 5 μm in diameter, with particle size being organ-dependent. Although reported in other studies, this is the first time that the three-dimensional nature of tiemannite is captured in marine mammal tissue.
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•First high-resolution SEM images of HgSe in marine mammal organs.•Indicates complex pathways of HgSe formation and transport between organs.•Organ-specific size of primary nanoparticles recorded.
A large, but poorly studied, bottlenose dolphin community, Tursiops truncatus, inhabits coastal waters of Normandy (Normano-Breton Gulf, English Channel, France). In this study, the social structure ...and abundance of this community were assessed using photo-identification techniques. Like other bottlenose dolphin communities worldwide, this resident community has a fission—fusion social structure with fluid associations among individuals (half-weight index = 0.10). Association patterns were highly variable as indicated by a high social differentiation (S = 0.95 ±0.03). The majority of associations were casual, lasting days to months. However, individuals exhibited also a smaller proportion of long-term relationships. A mean group size of 26 was large compared with other resident coastal communities, and variable, ranging from 1 to 100, which could be the results of ecological conditions, in particular resource predictability and availability. Analyses also showed that the community was organized in 3 social clusters that were not completely isolated from each other. Abundance was estimated at 420 dolphins (95% confidence interval: 331–521), making this coastal community one of the largest identified along European coastlines. Because human activities in the Gulf are expected to increase in the upcoming years, long-term demographic monitoring of this dolphin community will be critical for its management.
Microplastics' (MPs) abundance, small size, and global distribution render them bioavailable to a variety of organisms directly or by trophic transfer, yet examinations in marine apex predators are ...currently limited. The present study investigated the occurrence of MPs sized 125 μm–5 mm in the gastrointestinal tract (GIT) of bottlenose dolphins (Tursiops truncatus) stranded in South Carolina, USA from 2017 to 2018. MPs, mostly fibers, were detected in all GITs (n = 7) of stranded bottlenose dolphins. Total suspected MPs ranged between 123 and 422 particles/individual, a high range among international studies. Comparison to other studies likely reflects differences in both methods and location. This is the first study from North America to quantify MPs in a small coastal cetacean outside Arctic waters and the first specifically in bottlenose dolphins (southeastern United States). Findings and methodology from this investigation can aid future studies examining MP in marine apex predators.
•Microplastics in all 7 gastrointestinal tracts of bottlenose dolphins examined•Microplastics may fragment in cetacean digestive tract.•Fibers dominant morphology observed; fragments, films, and foams also present•Comparison to other studies likely reflects differences in methods and location.•Pathways of exposure and potential impacts on dolphins are still poorly understood.
According to theory, individuals forage in ways that maximize net energy intake. Distinct foraging strategies may emerge within a population in response to heterogeneous resources, competition and ...learning, among other drivers. We assessed individual variation in, and ecological consequences of, an unusual, specialized foraging tactic between animals and humans. In southern Brazil, bottlenose dolphins, Tursiops truncatus, herd fish schools towards artisanal fishermen, who cast nets in response to behavioural cues from the dolphins. This apparent cooperative tactic likely involves costs as well as benefits for both interacting parties, but such trade-offs remain poorly understood, especially for dolphins. We show that individual dolphins vary markedly in the frequency with which they interact with fishermen, and that this foraging variation is linked to ranging behaviour. Not all individual dolphins interact with fishermen; those that routinely do so concentrate around the limited interaction sites and have smaller home ranges than independent foragers. This suggests that foraging with fishermen increases foraging success and reduces search costs (i.e. foraging range). Competition for interaction sites may offset such benefits, since some individuals often forage at the high-quality sites while others forage at low-quality sites. Taken together, our findings suggest that two alternative tactics emerge in the population from trade-offs involving food access, foraging area, learning techniques and competition: dolphins either forage by themselves over larger areas on unpredictable resource patches (passing fish schools), or learn to interact with fishermen to access and compete for more predictable resource patches (interaction sites). By revealing some of the ecological drivers of this remarkable human–animal interaction, our study contributes two broader insights. First, specialized foraging can have ranging consequences for individuals and so structure the population spatially; second, interspecific cooperation may be founded upon intraspecific competition.
•We assess ecological drivers and consequences of foraging variation in dolphins.•Two tactics emerge from trade-offs involving foraging area, learning and competition.•Some individuals forage independently over larger areas on passing fish schools.•Others remain around specific sites to forage cooperatively with fishermen.•Our study shows how specialized foraging can structure populations spatially.
Estimates of the energetic costs of locomotion (COL) at different activity levels are necessary to answer fundamental eco-physiological questions and to understand the impacts of anthropogenic ...disturbance to marine mammals. We combined estimates of energetic costs derived from breath-by-breath respirometry with measurements of overall dynamic body acceleration (ODBA) from biologging tags to validate ODBA as a proxy for COL in trained common bottlenose dolphins (Tursiops truncatus). We measured resting metabolic rate (RMR); mean individual RMR was 0.71-1.42 times that of a similarly sized terrestrial mammal and agreed with past measurements that used breath-by-breath and flow-through respirometry. We also measured energy expenditure during submerged swim trials, at primarily moderate exercise levels. We subtracted RMR to obtain COL, and normalized COL by body size to incorporate individual swimming efficiencies. We found both mass-specific energy expenditure and mass-specific COL were linearly related with ODBA. Measurements of activity level and cost of transport (the energy required to move a given distance) improve understanding of the COL in marine mammals. The strength of the correlation between ODBA and COL varied among individuals, but the overall relationship can be used at a broad scale to estimate the energetic costs of disturbance and daily locomotion costs to build energy budgets, and investigate the costs of diving in free-ranging animals where bio-logging data are available. We propose that a similar approach could be applied to other cetacean species.
The 2010 Deepwater Horizon(DWH) disaster resulted in large-scale oil contamination of the northern Gulf of Mexico. As part of the Natural Resource Damage Assessment designed to investigate the ...potential impacts of the DWH oil spill, comprehensive health assessments were conducted on bottlenose dolphins Tursiops truncatus living in oiled bays (Barataria Bay BB, Louisiana, and Mississippi Sound , Mississippi/Alabama) and a reference bay with no evidence of DWH oil contamination (Sarasota Bay SB, Florida). As previously reported, multiple health issues were detected in BB dolphins during 2011. In the present study, follow-on capture-release health assessments of BB dolphins were performed (2013, 2014) and indicated an overall improvement in population health, but demonstrated that pulmonary abnormalities and impaired stress response persisted for at least 4 yr after the DWH disaster. Specifically, moderate to severe lung disease remained elevated, and BB dolphins continued to release low levels of cortisol in the face of capture stress. The proportion of guarded or worse prognoses in BB improved over time, but 4 yr post-spill, they were still above the proportion seen in SB. Health assessments performed in MS in 2013 showed similar findings to BB, characterized by an elevated prevalence of low serum cortisol and moderate to severe lung disease. Prognosis scores for dolphins examined in MS in 2013 were similar to BB in 2013. Data from these follow-on studies confirmed that dolphins living in areas affected by the DWH spill were more likely to be ill; however, some improvement in population health has occurred over time.
Gastrointestinal disease is a leading cause of morbidity in bottlenose dolphins (Tursiops truncatus) under managed care. Fecal microbiota transplantation (FMT) holds promise as a therapeutic tool to ...restore gut microbiota without antibiotic use. This prospective clinical study aimed to develop a screening protocol for FMT donors to ensure safety, determine an effective FMT administration protocol for managed dolphins, and evaluate the efficacy of FMTs in four recipient dolphins.
Comprehensive health monitoring was performed on donor and recipient dolphins. Fecal samples were collected before, during, and after FMT therapy. Screening of donor and recipient fecal samples was accomplished by in-house and reference lab diagnostic tests. Shotgun metagenomics was used for sequencing. Following FMT treatment, all four recipient communities experienced engraftment of novel microbial species from donor communities. Engraftment coincided with resolution of clinical signs and a sustained increase in alpha diversity.
The donor screening protocol proved to be safe in this study and no adverse effects were observed in four recipient dolphins. Treatment coincided with improvement in clinical signs.
•Robust abundance estimates for five cetacean species in EU Atlantic shelf waters.•No evidence for large-scale change in abundance between 1994 and 2005 in 3 species.•Large shift in harbour porpoise ...distribution demonstrated by spatial modelling.•Results allow assessment of conservation status at large spatial scale.
The European Union (EU) Habitats Directive requires Member States to monitor and maintain at favourable conservation status those species identified to be in need of protection, including all cetaceans. In July 2005 we surveyed the entire EU Atlantic continental shelf to generate robust estimates of abundance for harbour porpoise and other cetacean species. The survey used line transect sampling methods and purpose built data collection equipment designed to minimise bias in estimates of abundance. Shipboard transects covered 19,725km in sea conditions ⩽Beaufort 4 in an area of 1,005,743km2. Aerial transects covered 15,802km in good/moderate conditions (⩽Beaufort 3) in an area of 364,371km2. Thirteen cetacean species were recorded; abundance was estimated for harbour porpoise (375,358; CV=0.197), bottlenose dolphin (16,485; CV=0.422), white-beaked dolphin (16,536; CV=0.303), short-beaked common dolphin (56,221; CV=0.234) and minke whale (18,958; CV=0.347). Abundance in 2005 was similar to that estimated in July 1994 for harbour porpoise, white-beaked dolphin and minke whale in a comparable area. However, model-based density surfaces showed a marked difference in harbour porpoise distribution between 1994 and 2005. Our results allow EU Member States to discharge their responsibilities under the Habitats Directive and inform other international organisations concerning the assessment of conservation status of cetaceans and the impact of bycatch at a large spatial scale. The lack of evidence for a change in harbour porpoise abundance in EU waters as a whole does not exclude the possibility of an impact of bycatch in some areas. Monitoring bycatch and estimation of abundance continue to be essential.
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