Common Dolphin Delphinus Delphis Research Articles

Development of an integrated indicator to assess chemical contamination in different marine species: The case of mercury on the French Atlantic continental shelf

Good Environmental Status (GES) for Descriptor 8 (D8) of the Marine Strategy Framework Directive (MSFD) is considered to be achieved when concentrations of contaminants are at levels not giving rise to pollution effects. This study proposes a framework to assess GES in marine waters adjacent to France, including four groups of species (bivalves, fish, birds and mammals) living on the continental shelf and covering different dimensions of the marine environment. This framework is applied to mercury (Hg) in the three marine regions along the French Atlantic coast and includes two assessment types: i) an absolute assessment by comparing contamination levels with environmental thresholds, and ii) a relative assessment by comparing contamination levels over time, performed for bivalves and mammals that had long time-series available. Mercury concentrations were higher than environmental thresholds for bivalves and fish in all the three studied regions. Plus, they significantly increased since the 2000s for most bivalve stations and for the common dolphin Delphinus delphis. Our results therefore indicate that Hg concentrations have increased in marine waters and have reached levels possibly giving rise to pollution effects in biota from the three marine regions. The present study also highlighted the complementarity of monitoring Hg concentrations in each group of species and each type of assessment, making it possible to propose a conceptual framework for assessing the environmental pressure of bioaccumulated and biomagnified contaminants over the continental shelf.

Elements in muscle tissue of three dolphin species from the east coast of South Africa

We investigated elemental concentrations in muscle tissue of three species of dolphins incidentally bycaught off the KwaZulu-Natal coastline, South Africa. Thirty-six major, minor and trace elements were analysed in Indian Ocean humpback dolphin Sousa plumbea (n = 36), Indo-Pacific bottlenose dolphin Tursiops aduncus (n = 32) and the Common dolphin Delphinus delphis (n = 8). Significant differences in concentration between the three species were observed for 11 elements (cadmium, iron, manganese, sodium, platinum, antimony, selenium, strontium, uranium, vanadium and zinc). Mercury concentrations (maximum 29 mg/kg dry mass) were generally higher than those reported for coastal dolphin species found elsewhere. Our results reflect a combination of species differences in habitat, feeding ecology, age, and possibly species physiology and exposure to pollution levels. This study confirms the high organic pollutant concentrations documented previously for these species from the same location, and provides a well-founded case for the need to reduce pollutant sources.

Tension pneumothorax in small odontocetes.

Pneumothorax, the accumulation of air in the pleural cavity, occurs when air enters the pleural space by the pleuro-cutaneous, pleuro-pulmonary, or pleuro-oesophageal-mediastinal route. Tension pneumothorax is an infrequent and severe form of pneumothorax where a positive pressure in the pleural space is built up during at least part of the respiratory cycle, with compression of both lungs and mediastinal vessels, and, if unilateral, with midline deviation towards the unaffected hemithorax. We describe 9 cases of tension pneumothorax in 3 species of small cetaceans (striped dolphin Stenella coeruleoalba, common dolphin Delphinus delphis, and common bottlenose dolphin Tursiops truncatus) from the western Mediterranean coast of Spain, and one case from a dolphinarium. Computed tomography (CT) imaging performed in 2 carcasses before necropsy showed lung compression, midline deviation, and pressure on the diaphragm, which was caudally displaced. Tension pneumothorax was recognized at necropsy by the presence of pressurized air in one of the hemithoraces. Seven of the pneumothorax cases were spontaneous (2 primary and 5 secondary to previous lung pathology). In the other 2 dolphins, the pneumothorax was traumatic, due to oesophageal-pleural perforation or rib fractures. We hypothesize that pneumothorax in dolphins is predominantly tensional because of their specific anatomical and physiological adaptations to marine life and the obligate exposure to extreme pressure changes as diving mammals.

Characterising injuries and pathologies of common dolphin Delphinus delphis mortalities in the South Australian Sardine Fishery

Mortality of dolphins in fishing operations is often under-estimated, as shown by studies of beach-washed carcasses. Linking evidence obtained during necropsies with fishing method is fundamental to understanding the extent of mortality and the manner in which animals die. The South Australian Sardine Fishery (SASF) has operated a purse-seine industry since 1991. This study characterised injuries, pathological changes and life history of 49 dead dolphins collected from SASF during 2006-2019. Histology examination was conducted on 25 animals. Neonates, calves and juveniles accounted for 63% of the sample. Of mature females (n = 14), 11 were pregnant or lactating, with cryptic mortality estimated to be 20% of dolphins studied. Body condition was robust in 48 dolphins. Net marks were seen on 82%, mostly on the head, trunk and peduncle. Broken/missing teeth were noted in 63%. All dolphins had subdermal haemorrhage (moderate to severe in 96%), particularly around the head. Deep haemorrhage was common, including around occipital and flipper condyles, and organs. Copious fluid was present in the thoracic (pleural) and abdominal (ascites) cavities of half of the dolphins. Within the lungs, watery fluid and froth were observed in 100 and 39%, respectively. Recent bone fractures were documented in 43% of dolphins, mostly associated with haemorrhage. Severe blunt trauma appeared to be the primary cause of death, and 10 dolphins also had other significant pathologies. Visceral organ congestion and mild cardiomyopathy were observed. Stomachs contained prey remains in 75% of cases. The results of this study may help identify unreported purse-seine mortalities washed up in South Australia and elsewhere.

Trophic ecology of northern gannets Morus bassanus highlights the extent of isotopic niche overlap with other apex predators within the Bay of Biscay

Understanding the linkages within complex and evolving marine food webs is essential to comprehend marine ecosystem structure and dynamics. Carbon (δ13C) and nitrogen (δ15N) stable isotope signatures are recognized to be powerful descriptors of the trophic ecology and trophic relationships within marine communities. Apex predators such as seabirds can influence the structure of communities by predating in lower trophic levels. They also convey information both over a range of spatial and temporal scales due to their high mobility and longevity, respectively. For this reason, here, we studied the trophic ecology of northern gannets and the extent of niche overlap with other apex predators within the Bay of Biscay (North-East Atlantic), a key feeding area for numerous predatory species. Mixing models indicated that northern gannets fed primarily on European anchovy Engraulis encrasicolus and on a mixed group composed of European sardine Sardina pilchardus, European sprat Sprattus sprattus, juvenile hake Merluccius merluccius, Atlantic mackerel Scomber scombrus and Atlantic horse mackerel Trachurus trachurus. Within the apex predator community, the northern gannets trophic niche overlapped the most with common guillemots Uria aalge (15.58%, based on Stable Isotope Bayesian Ellipses (SIBER)) and overlapped to a lesser extent with cetacean species occupying shelf habitats (i.e., the harbour porpoise Phocoena phocoena (9.99%) and the short-beaked common dolphin Delphinus delphis (10.37%)). Overall, the overlap found was moderate indicating trophic similarities and dissimilarities between these species. Information on trophic interactions between co-existing species is necessary for holistic environmental management, particularly in areas where several megafauna species share their foraging grounds with fisheries activity.

Predatory species left stranded following the collapse of the sardine Sardinops sagax (Pappe, 1854) stock off the northern Benguela upwelling system: A review

Sardine Sardinops sagax (Pappe, 1854) is an important forage species, in the northern Benguela Upwelling System (nBUS). Sardine was a key forage species of the pelagic component in the nBUS, but the population collapsed due to a combination of overfishing and ecosystem change and variability in the nBUS. Multiple predators depended on sardine as high-quality food at the time when it was abundant. This study reviewed the current knowledge of predators' diet pre- and post-collapse of the sardine population stock in the nBUS. Data were sourced from previous studies on the trophic interaction in the nBUS. The historical and contemporary diets of commercially exploited species that prey on sardine were found to be relatively well documented while there are data deficiencies for non-commercially exploited species including cetaceans, sharks and some non-commercially exploited fish species. Amongst the species most reliant on sardine as prey are African penguin Spheniscus demersus, Cape gannet Morus capensis, Cape cormorant Phalacrocorax capensis, Cape monkfish Lophius vomerinus, shallow-water hake Merluccius capensis, deep-water hake M. paradoxus, snoek Thyrsites atun, Albacore tuna Thunnus alalunga, Cape fur seal Arctocephalus pusillus, Common dolphins Delphinus delphis, Dusky dolphins Lagenorhynchus obscurus, Heaviside's dolphins Cephalorhynchus heavisidii, six gills shark Hexanchus griseus, copper sharks Carcharhinus brachyurus, school shark Galeorhinus galeus and pelagic sharks Prionace glauca. Some predatory species such as the African penguin, Cape cormorant, Cape gannet, and school shark, are considered endangered as per the International Union for the Conservation of Nature (IUCN) Red List criteria. Populations of Albacore tuna and Cape monkfish are near threatened, while Cape fur seals, common dolphins, and shallow-water hake are considered the least concerned on the IUCN list. Although the collapse of sardine has affected the food webs it has not resulted in collapse, rather there have been changes. Three prey species; bearded goby, Cape horse mackerel, and jellyfish, were identified as alternative prey for some of the predators that previously fed on sardine. This review showed how overexploitation of sardine could have had far-reaching effects on the nBUS through feeding linkages. Goby, although a low-quality prey, is a successful substitute for sardine probably mostly due to its high abundance, tolerance to low oxygen and ability to thrive in warm waters. However, further studies are needed to establish the strength of the ecological linkages of the prey species that replaced sardine in the diets of the predators.

Cetacean community off French Guiana

Although human activities are developing in French Guiana Exclusive Economic Zone (EEZ) and surrounding countries, knowledge on diversity and ecology of cetaceans in the region is scarce. This study aimed to collect new information on the cetacean species occurring year-round in the entire French Guiana EEZ by combining visual and acoustic data obtained from three boat-based campaigns conducted by local NGOs. The GEPOG campaign was conducted from July 2011 to June 2012, four days every two months; the COHABYS campaign was performed five days per month from January to May 2018; the OSL campaign consisted in four 10-day surveys conducted in June, July, September and October 2018. The visual observation effort conducted when Beaufort sea state < 5 was 1,961 km, 1,491 km and 3,243 km respectively. Acoustic records were done when Beaufort sea state < 5 during daylight and/or nighttime, depending on the survey. A total of 132 cetacean sightings were done. Five cetacean families and 15 species were identified. Delphinidae was the family most frequently sighted (91% to 100% of groups and 99% to 100% of individuals per campaign). The most frequent species in the area were identified, along with their distribution and phenology: Guiana dolphin (Sotalia guianensis) was found in the coastal area (0-20 m), the long-beaked common dolphin (Delphinus delphis) was sighted on the shelf (20-100 m), along with the bottlenose dolphin (Tursiops truncatus) and the Atlantic spotted dolphin (Stenella frontalis) that were also common on the upper slope (100-1,500 m). Finally, the spinner dolphin (Stenella longirostris), the melon-headed whale (Peponocephala electra) and the pantropical spotted dolphin (Stenella attenuata) were frequent on the slope (100-3,500 m). The results suggest these species may be found in French Guiana waters all year round and mother and calf pairs, as indicator of reproduction, were observed for all of them except the long-beaked common dolphin and the Guiana dolphin. Mother and calf pairs of humpback whales (Megaptera novaeangliae), that potentially belong to the “A” stock, were also sighted twice, as well as two groups of sperm whales (Physeter macrocephalus) with calves. Hence, these results showed that French Guiana bears a particular responsibility for the conservation of cetacean biodiversity, but a lot remains to be done to strengthen knowledge and conservation of these species in the territory.

Vaginal Calculi in the Eastern North Atlantic Common Dolphins Delphinus Delphis, Induction Mechanisms and Possible Effects on Fecundity

The proper management of cetacean populations requires life history and demographic parameters to be estimated at population level. In this study we focus on a reproductive pathology that has the potential to alter reproductive rate: the vaginal calculi or stones. The present work documents vaginal calculi prevalence and structure in the eastern North Atlantic common dolphin Delphinus delphis in order to infer their likely mechanisms of induction and possible effects on fecundity. The work is based on routine examinations and necropsies of stranded marine mammals reported by the French stranding scheme from 1972 to 2012. Vaginal calculi were described and measured, and their composition was analyzed by Fourrier-Transformed Infra-Red (FTIR) spectroscopy. Necropsies and reproductive tract examinations were performed on 435 female common dolphins since 1972 along the French coasts, of which 14 showed vaginal calculi, representing 3.2% of the examined females. All females with calculi were older than 7, and there was no relationship of calculus size with age. Histopathology revealed lesions due to an inflammatory response to the presence of the calculi: chronicle vaginitis, variable endometritis and cystitis. Calculus size varied from 1 to 21 cm in maximum dimension and 4–1,460 g in mass. Their internal structure was homogeneous, particularly due to the absence of core material, hence corresponding to the definition of primary calculi. All calculus spectra showed almost identical compositions, with struvite (magnesium ammonium phosphate hexahydrate) representing on average 87% of calculus mass. Dysfunction of the uro-genital tract, such as vesico-vaginal fistulae, would be the likely initial pathological condition that led to the formation of these stones. Both the initial chemical condition in the vagina and the resulting formation of a calculi are obstacles to successful reproduction.

First records of the pantropical spotted dolphin <i>Stenella attenuata</i>, within groups of common dolphins <i>Delphinus delphis</i> in northern Peru

Although dolphins are mostly known to form single species groups of varying size, occasionally they aggregate in mixed-species groups. The presence of mixed-species delphinid groups along the Peruvian coast is unknown. Herein, we report the presence of a single pantropical spotted dolphin (Stenella attenuata) within large groups of the common dolphin (Delphinus delphis) at Los Organos in the northern coast of Peru. Sightings occurred on October 10th, 2016, January 7th, 2018 and September 21st, 2019. In one sighting the mixed group was feeding, while during the other two sightings the group was travelling. These records add new evidence about mixed-species delphinid groups in coastal waters of Peru.

Determinants of lungworm specificity in five cetacean species in the western Mediterranean

BackgroundCurrent data about Pseudaliidae show contrasting patterns of host specificity between congeneric species. We investigated how both contact and compatibility between hosts and parasites contributed to the patterns of lungworm infection observed in a community of five species of cetaceans in the western Mediterranean.MethodsThe lungs of 119 striped dolphins Stenella coeruleoalba, 18 bottlenose dolphins Tursiops truncatus, 7 Risso’s dolphins Grampus griseus, 7 long-finned pilot whales Globicephala melas, and 6 common dolphins Delphinus delphis were analysed for lungworms. Parasites were identified by morphology and analysis of ITS2 sequences using both maximum likelihood and Bayesian inference methods. Body length was used as a proxy for lungworm species fitness in different hosts and compared with Kruskal-Wallis tests. Infection parameters were compared between cetacean species using Fisher’s exact tests and Kruskal-Wallis tests. Phylogenetic specificity was explored by collating the overall lungworm species prevalence values in hosts from previous surveys in various localities. To explore the relative importance of vertical and horizontal transmission, Spearman’s rank correlation was used to look for an association between host size and lungworm burden. A Mantel test was used to explore the association between lungworm species similarity and prey overlap using dietary data.ResultsHalocercus delphini had higher infection levels in striped dolphins and common dolphins; Stenurus ovatus had higher infection levels in bottlenose dolphins; and Stenurus globicephalae had higher infection levels in long-finned pilot whales. These results are congruent with findings on a global scale. Morphometric comparison showed that the larger nematodes were found in the same host species that had the highest parasite burden. Lungworms were found in neonatal striped dolphins and a Risso’s dolphin, and there was a weak but significant correlation between host size and parasite burden in striped dolphins and bottlenose dolphins. There was also a weak but significant association between prey overlap and lungworm species similarity.ConclusionsData indicate that phylogenetic specificity has an important role in governing host–parasite associations, as indicated by the higher infection levels and larger nematode size in certain hosts. However, diet can also influence infection patterns in these preferred hosts and contribute to less severe infections in other hosts.Graphical

A new delphinid from the lower Pliocene of the North Sea and the early radiations of true dolphins

Abstract. With a remarkable exception for the Mediterranean, the worldwide Pliocene record of true dolphins (Cetacea, Odontoceti, Delphinidae) remains scarce, in stark contrast with the large number of extant species testifying to the evolutionary success of this family. Based on a fragmentary skull discovered in lower Pliocene deposits (Zanclean, 5 to 4.4 Ma) of the Kattendijk Formation in the Antwerp harbour (Belgium, southern margin of the North Sea basin), we describe here a new delphinid species, Pliodelphis doelensis gen. et sp. nov. This small dolphin with cranial dimensions in the range of the short-beaked common dolphin Delphinus delphis can be distinguished from other extinct and extant delphinids by a combination of cranial features including the maxilla being significantly narrower than the premaxilla at a short distance anterior to the antorbital notch in dorsal view, the maximum opening of the mesorostral groove being located at the level of the antorbital notches, a transversely wide and anteroposteriorly long dorsal exposure of the presphenoid anterior to the bony nares, and all dorsal infraorbital foramina being located posterior to the premaxillary foramina. P. doelensis constitutes the first member of the family described from the early Pliocene of the North Sea basin and, for the whole North Atlantic realm, only the third outside the Mediterranean. This new record contributes thus to our understanding of the poorly known Pliocene radiation(s) of true dolphins.

Intraspecific variation in short-beaked common dolphin’s whistle repertoire

ABSTRACT Dolphins’ whistles are strongly diversified mainly related to physiology and behaviour. We present the whistle characteristics and intraspecific variations of short-beaked common dolphins Delphinus delphis of the Western South Atlantic Ocean (WSAO). A total of 1630 whistles from six encounters were analysed considering group size, contours and acoustical parameters. No significant correlation was found (p > 0.05) between number of whistles and the group size. Upsweep, downsweep and constant were the most frequent contours. A positive relation between the downsweep contour and group size was detected (p < 0.05). Minimum, maximum, centre, peak, initial and final frequencies, frequency range, frequency gradient, duration and inflection points were extracted. The frequencies ranged from 1.34 to 35.23 kHz and the duration varied from 0.11 to 2.16 seconds. Comparing encounters between years through Bonferroni method, minimum frequency, duration, and frequency range were significantly different. C5.0 decision tree showed that whistles of 2014 and 2015 had correct classifications (67.0% and 54.0%, respectively). The nMDS grouped the Atlantic and Pacific oceans based on inflection points and duration, further corroborated through PERMANOVA (p < 0.05). Our results suggest the influence of certain parameters related to intraspecific variation. Whistles comparison with other localities corroborates with differences in geographical scale.

Brucella ceti sequence type 23, 26, and 27 infections in North American cetaceans.

Brucella ceti infection is associated with a variety of disease outcomes in cetaceans globally. Multiple genotypes of B. ceti have been identified. This retrospective aimed to determine if specific lesions were associated with different B. ceti DNA sequence types (STs). Characterization of ST was performed on 163 samples from 88 free-ranging cetaceans, including common bottlenose dolphin Tursiops truncatus (T.t.; n = 73), common short-beaked dolphin Delphinus delphis (D.d.; n = 7), striped dolphin Stenella coeruleoalba (n = 3), Pacific white-sided dolphin Lagenorhynchus obliquidens (n = 2), sperm whale Physeter macrocephalus (n = 2), and harbour porpoise Phocoena phocoena (n = 1), that stranded along the coast of the US mainland and Hawaii. ST was determined using a previously described insertion sequence 711 quantitative PCR. Concordance with 9-locus multi-locus sequence typing was assessed in a subset of samples (n = 18). ST 26 was most commonly identified in adult dolphins along the US east coast with non-suppurative meningoencephalitis (p = 0.009). Animals infected with ST 27 were predominately perinates that were aborted or died shortly after birth with evidence of in utero pneumonia (p = 0.035). Reproductive tract inflammation and meningoencephalitis were also observed in adult T.t. and D.d. with ST 27, though low sample size limited interpretation. ST 23 infections can cause disease in cetacean families other than porpoises (Phocoenidae), including neurobrucellosis in D.d. In total, 11 animals were potentially infected with multiple STs. These data indicate differences in pathogenesis among B. ceti STs in free-ranging cetaceans, and infection with multiple STs is possible.

Spatiotemporal models highlight influence of oceanographic conditions on common dolphin bycatch risk in the Bay of Biscay

The population of short-beaked common dolphins Delphinus delphis of the Bay of Biscay (northeast Atlantic) has been subjected to potentially dangerous levels of bycatch since the 1990s. As the phenomenon intensifies, it represents a potent threat to the population. Here, we investigated the relationship between bycatch mortality and oceanographic processes. We assumed that oceanographic processes spatiotemporally structure the availability and aggregation of prey, creating areas prone to attract both common dolphins and fish targeted by fisheries. We used 2 datasets from 2012 to 2019: oceanographic data resulting from a circulation model and mortality data inferred from strandings. The latter allows location of mortality areas and quantification of the intensity of mortality events at sea. We fitted a series of spatiotemporal hierarchical Bayesian models using integrated nested Laplace approximations (INLA). Results provided first insights on how bycatch of common dolphins in the Bay of Biscay might be related to key seasonal and dynamic oceanographic features. We showed that from a statistical predictive point of view, the monthly trend of 2019 bycatch mortality could be predicted with few oceanographic covariates. This study highlights how gaining knowledge about environmental influences on interactions between short-beaked common dolphins and fisheries could have great conservation and management value. Identified relationships with oceanographic covariates were complex, as expected given the dynamic aspects of oceanographic processes, dolphins and fisheries distributions. Further research focusing on smaller time scales is needed to elucidate proximal drivers of common dolphin bycatch in the Bay of Biscay.

Systemic Erysipelothrix rhusiopathiae in seven free-ranging delphinids stranded in England and Wales.

Microbiology records for 1127 cetaceans stranded on English and Welsh beaches and examined at the Institute of Zoology between 1990 and 2019 were reviewed to identify cases of Erysipelothrix rhusiopathiae, an uncommon but potentially fatal zoonotic pathogen. Once cases were identified, prevalence was calculated, corresponding postmortem reports were reviewed, common gross and histopathological findings were identified, and antibiotic susceptibilities were determined. Overall prevalence for E. rhusiopathiae was 0.62% (7/1127; 95% CI: 0.30-1.28%). It was isolated from 3 bottlenose dolphins Tursiops truncatus, 3 harbor porpoises Phocoena phocoena, and 1 short-beaked common dolphin Delphinus delphis, with a prevalence of 21.4% (3/14; 95% CI: 7.6-47.9%), 0.39% (3/779; 95% CI: 0.13-1.13%), and 0.47% (1/212; 95% CI: 0.08-2.62%) for each species, respectively. E. rhusiopathiae resulted in septicemia in all cases from which it was isolated. Gross necropsy findings included pulmonary edema (5/7), hemorrhage (5/7) and/or congestion of various organs (4/7), and serosanguineous effusion (3/7; pericardial: 3/7, pleural: 2/6, abdominal: 2/6). Congestion (5/5), bacterial emboli (4/5), and hemorrhage (4/5) were commonly observed on histopathology, and acute renal tubular injury (2/5) and pulmonary edema (2/5) were occasionally observed. Routine bacterial cultures were vital in identifying E. rhusiopathiae, since gross lesions were often subtle and nonspecific. The liver, kidney, and brain were key organs from which E. rhusiopathiae was consistently isolated. Antibiotic resistance was uncommon and was only observed for amikacin and trimethoprim sulfonamide. Penicillins were consistently effective, along with fluoroquinolones, macrolides, clindamycin, cephalexin, and oxytetracycline.

Meningoencephalitis in a common minke whale Balaenoptera acutorostrata associated with Brucella pinnipedialis and gamma-herpesvirus infection.

Fatal marine Brucella infections with histologic lesions specific to the central nervous system (CNS), known as neurobrucellosis, have been described in 5 species of odontocete cetaceans in the UK: striped dolphins Stenella coeruleoalba, Atlantic white-sided dolphins Lagenorhynchus acutus, short-beaked common dolphins Delphinus delphis, long-finned pilot whale Globicephala melas and Sowerby's beaked whale Mesoplodon bidens. To date, these CNS lesions have only been associated with Brucella ceti ST26 and not with B. pinnipedialis, which is rarely isolated from cetaceans and, although commonly found in various seal species, has never been associated with any pathology. This paper describes the first report of neurobrucellosis in a common minke whale Balaenoptera acutorostrata which was associated with the isolation of Brucella pinnipedialis ST24 and co-infection with Balaenoptera acutorostrata gamma-herpesvirus 2. This is the first report of neurobrucellosis in any species of mysticete and the first report of Brucella pinnipedialis in association with any pathology in any species of marine mammal, which may be due to co-infection with a herpesvirus, as these are known to be associated with immunosuppression.

Causes of cetacean stranding and death on the Catalonian coast (western Mediterranean Sea), 2012-2019.

The causes of cetacean stranding and death along the Catalan coast between 2012 and 2019 were systematically investigated. Necropsies and detailed pathological investigations were performed on 89 well-preserved stranded cetaceans, including 72 striped dolphins Stenella coeruleoalba, 9 Risso's dolphins Grampus griseus, 5 bottlenose dolphins Tursiops truncatus, 1 common dolphin Delphinus delphis, 1 Cuvier's beaked whale Ziphius cavirostris and 1 fin whale Balaenoptera physalus. The cause of death was determined for 89.9% of the stranded cetaceans. Fisheries interaction was the most frequent cause of death in striped dolphins (27.8%) and bottlenose dolphins (60%). Cetacean morbillivirus (CeMV) was detected on the Catalan coast from 2016 to 2017, causing systemic disease and death in 8 of the 72 (11.1%) striped dolphins. Chronic CeMV infection of the central nervous system was observed from 2018-2019 in a further 5 striped dolphins. Thus, acute and chronic CeMV disease caused mortality in 18% of striped dolphins and 14.6% of all 89 cetaceans. Brucella ceti was isolated in 6 striped dolphins and 1 bottlenose dolphin with typical brucellosis lesions and in 1 striped dolphin with systemic CeMV. Sinusitis due to severe infestation by the nematode parasite Crassicauda grampicola caused the death of 4 out of 6 adult Risso's dolphins. Maternal separation, in some cases complicated with septicemia, was a frequent cause of death in 13 of 14 calves. Other less common causes of death were encephalomalacia of unknown origin, septicemia, peritonitis due to gastric perforation by parasites and hepatitis caused by Sarcocystis spp.

Seasonal dynamics of occurrence and group size of three species of cetaceans (Delphinidae and Phocoenidae) on the southwestern coast of the Black Sea

The spatial and temporal occurrence of cetaceans in the Black Sea and particularly along its southwestern coastline is poorly studied. Based on a total of 609 encounters, we present the analysis of monthly dynamics of (1) the numbers of cetacean sightings and (2) their group size for all three Black Sea cetacean species: the bottlenose dolphin (Tursiops truncatus), the short-beaked common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) over a continuous period of 29 months (January 2018 - May 2020) from two fixed coastal observation points near the city of Zonguldak, Turkey. Seasonal fluctuations were found in the occurrence of all three species, with peaks in April-May (spring). Similarly, the largest groups of P. phocoena and T. truncatus were recorded in the late spring and early summer period, while D. delphis had a peak in July (summer). In case of the harbour porpoise, we speculate that these variations can be explained by the annual migrations from the northwestern to southern waters of the Black Sea, while the seasonal dynamics of the two Delphinidae species might depend on fish prey availability. While our data were collected locally, the results provide better insight into the ecology of cetaceans within the entire Black Sea.

Common dolphin Delphinus delphis occurrence off the Wild Coast of South Africa

Despite their typical large group sizes, limited research exists on the occurrence of common dolphins Delphinus delphis because of the pelagic, offshore nature of this species and the lack of barriers to their movement in this environment. The main purpose of our study was to investigate the occurrence of common dolphins off the Wild Coast of South Africa (western Indian Ocean) and whether spatiotemporal and environmental conditions affected their encounter rate, relative abundance and mean group size. The annual sardine run in this region, during austral winter (May to July), is considered a main driver of dolphin occurrence; however, our boat-based surveys over the period 2014–2016 indicated that common dolphins occur and feed in this area outside of this time-frame. In terms of environmental factors, the largest group (∼1 250 animals) was found in the deepest waters. Additionally, at Hluleka, dolphins were observed primarily feeding, which could suggest that this coastal area is highly productive. As common dolphin distribution is thought to be correlated with prey distribution, our findings suggest that sufficient prey exists along the Wild Coast both during and outside the annual sardine run to sustain large groups of the dolphins and that their presence in the area is not solely a function of the sardine run.

Stranded cetaceans warn of high perfluoroalkyl substance pollution in the western Mediterranean Sea

Perfluoroalkyl substances (PFASs) are a class of organohalogenated compounds of environmental concern due to similar characteristics as the well-studied legacy persistent organic pollutants (POPs) that typically show environmental persistence, biomagnification and toxicity. Nevertheless, PFAS are still poorly regulated internationally and in many aspects poorly understood. Here, we studied liver and muscle concentrations in five cetacean species stranded at the southeastern coast of Spain during 2009–2018. Twelve of the fifteen targeted compounds were detected in >50% of the liver samples. Hepatic concentrations were significantly higher than those in muscle reflecting the particular toxicokinetics of these compounds. Bottlenose dolphins Tursiops truncatus showed the highest hepatic ΣPFAS (n = 5; 796.8 ± 709.0 ng g−1 ww) concentrations, followed by striped dolphin Stenella coeruleoalba (n = 29; 259.5 ± 136.2 ng g−1 ww), sperm whale Physeter macrocephalus (n = 1; 252.8 ng g−1 ww), short-beaked common dolphin Delphinus delphis (n = 2; 240.3 ± 218.6 ng g−1 ww) and Risso’s dolphin Grampus griseus (n = 1; 78.7 ng g−1 ww). These interspecies differences could be partially explained by habitat preferences, although they could generally not be related to trophic position or food chain proxied by stable N (δ15N) and C (δ13C) isotope values, respectively. PFAS profiles in all species showed a similar pattern of concentration prevalence in the order PFOS>PFOSA>PFNA≈PFFUnA>PFDA. The higher number of samples available for striped dolphin allowed for evaluating their PFAS burden and profile in relation to the stranding year, stable isotope values, and biological variables including sex and length. However, we could only find links between δ15N and PFAS burdens in muscle tissue, and between stranding year and PFAS profile composition. Despite reductions in the manufacturing industry, these compounds still appear in high concentrations compared to more than two decades ago in the Mediterranean Sea and PFOS remains the dominating compound.