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Our study aims to assess the population connectivity, evolutionary history, and conservation status of the short-beaked common dolphin in the Black Sea and Turkish Straits System (TSS). We also include DNA sequences from the Atlantic Ocean and the Mediterranean Sea to provide a regional perspective to our localized study. Analysis of 366 base pairs of mitochondrial DNA D-loop fragments from 37 samples collected from short-beaked common dolphins in the Black Sea, TSS, and Aegean Sea revealed 13 haplotypes, eight of which have not been previously reported. While analysis of samples archived on GenBank revealed 89 different haplotypes across the region. The haplotype network contains two main peripheral groups that include individuals from all locations. Haplotypes from the Atlantic Ocean are scattered across the network and no obvious population separation was detected. Some shared haplotypes potentially indicate multi-directional colonization events of the Mediterranean Sea from the eastern Atlantic Ocean. Moreover, some less widely distributed haplotypes suggest some level of more recent genetic connectivity through the Strait of Gibraltar and the TSS and point out the importance of these straits in the dispersal of short-beaked common dolphins. The haplotype and nucleotide diversity values were lower in the Black Sea, TSS, and western Mediterranean Sea when compared to the Atlantic Ocean, supporting the expansion of Atlantic populations into the Mediterranean and the Black Seas. Differentiation was observed between the Atlantic Ocean, and the Mediterranean Sea, TSS and the Black Sea based on Фst but not between Mediterranean and the Black Seas. For common dolphins, which have high dispersal potential, the protection of open seas and narrow seaways to enhance connectivity may be crucial.

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Marine litter is a global challenge and society plays an important role via lifestyles and behaviour, including policy support. We analysed public perceptions of marine litter and contributing factors, using data from 1133 respondents across 16 European countries. People reported high levels of concern about marine litter, and the vast majority (95%) reported seeing litter when visiting the coast. The problem was attributed to product and packaging design and behaviour rather than lack of facilities or accidental loss of items. Retailers, industry and government were perceived as most responsible, but also least motivated and competent to reduce marine litter, whereas scientists and environmental groups were perceived as least responsible but most motivated and competent. Regression analyses demonstrated the importance of psychological factors such as values and social norms above sociodemographic variables. These findings are important for communications and interventions to reduce inputs of marine litter to the natural environment.

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Our study reports the first data on mercury (Hg) isotope composition in marine European fish, for seven distinct populations of the European seabass, Dicentrarchus labrax. The use of δ202Hg and Δ199Hg values in SIBER enabled us to estimate Hg isotopic niches, successfully discriminating several populations. Recursive-partitioning analyses demonstrated the relevance of Hg stable isotopes as discriminating tools. Hg isotopic values also provided insight on Hg contamination sources for biota in coastal environment. The overall narrow range of δ202Hg around Europe was suggested to be related to a global atmospheric contamination while δ202Hg at some sites was linked either to background contamination, or with local contamination sources. Δ199Hg was related to Hg levels of fish but we also suggest a relation with ecological conditions. Throughout this study, results from the Black Sea population stood out, displaying a Hg cycling similar to fresh water lakes. Our findings bring out the possibility to use Hg isotopes in order to discriminate distinct populations, to explore the Hg cycle on a large scale (Europe) and to distinguish sites contaminated by global versus local Hg source. The interest of using Hg sable isotopes to investigate the whole European Hg cycle is clearly highlighted.

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[This corrects the article DOI: 10.1371/journal.pone.0172970.].

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Marine traffic is threatening cetaceans on a local and global scale. The Istanbul Strait is one of the busiest waterways, with up to 2,500 vessels present daily. This is the first study to assess the magnitude of short- and long-term behavioural changes of the endangered Black Sea harbour porpoises (Phocoena phocoena relicta) in the presence of marine vessels within the Istanbul Strait. Markov chains were used to investigate the effect of vessel presence on the transition probability between behavioural states (diving, surface-feeding and travelling), and to quantify the effect on the behavioural budget and bout length (duration of time spent in a given state) of porpoises. Further, the changes on swimming directions of porpoises in relation to vessel speed and distance was investigated using generalized linear models. In vessel presence, porpoises were less likely to remain in a given behavioural state and instead more likely to switch to another state. Because of this, the bout length of all three behavioural states decreased significantly in the presence of vessels. The vessel effect was sufficiently large to alter the behavioural budget, with surface-feeding decreasing significantly in the presence of vessels. However, when taking into account the proportion of time that porpoises were exposed to vessels (i.e. 50%), the measured effect size was not large enough to significantly alter the animals' cumulative (diurnal) behavioural budget. Additionally, vessel speed and distance had a significant effect on the probability of porpoises showing a response in their swimming directions. The southern and middle sections of the Istanbul Strait, which have the heaviest marine traffic pressure, had the lowest porpoise sightings throughout the year. Conversely, northern sections that were exposed to a lesser degree of marine traffic hold the highest porpoise sightings. The effect shown in this study in combination with increasing human impacts within the northern sections should be considered carefully and species-specific conservation actions, including establishment of protected areas, should be put in place to prevent the long-term consequences of marine traffic on the Black Sea harbour porpoise population.

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Genetic population structure of geographically isolated endangered Black Sea harbor porpoise (Phocoena phocoena relicta) is little known in Turkish waters, especially in the Turkish Straits System (TSS- Marmara Sea, Bosphorus and Dardanelles), which connects the Black Sea and the Aegean Sea. Mitochondrial DNA sequences of 70 new individuals sampled in the Turkish Black Sea, TSS and Aegean Sea, revealed five new haplotypes from the Black Sea. The findings support the idea that harbor porpoises from the Black Sea dispersed into the Aegean through the TSS. Considering signatures of population expansion, all subpopulations showed a signature of population expansion. The network data and the Фst calculations indicated that the Marmara Sea subpopulation was significantly differentiated from all of the other subpopulations, and supports the notion of its isolated. The finding of a potential management unit (MU) within an already heavily impacted subpopulation as a whole suggests that the individuals of P. p. relicta inhabiting the Marmara Sea require a very rigorous conservation strategy to ensure the survival of this subpopulation, represented by its unique haplotype.

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The population structure of the highly mobile marine mammal, the harbor porpoise (Phocoena phocoena), in the Atlantic shelf waters follows a pattern of significant isolation-by-distance. The population structure of harbor porpoises from the Baltic Sea, which is connected with the North Sea through a series of basins separated by shallow underwater ridges, however, is more complex. Here, we investigated the population differentiation of harbor porpoises in European Seas with a special focus on the Baltic Sea and adjacent waters, using a population genomics approach. We used 2872 single nucleotide polymorphisms (SNPs), derived from double digest restriction-site associated DNA sequencing (ddRAD-seq), as well as 13 microsatellite loci and mitochondrial haplotypes for the same set of individuals. Spatial principal components analysis (sPCA), and Bayesian clustering on a subset of SNPs suggest three main groupings at the level of all studied regions: the Black Sea, the North Atlantic, and the Baltic Sea. Furthermore, we observed a distinct separation of the North Sea harbor porpoises from the Baltic Sea populations, and identified splits between porpoise populations within the Baltic Sea. We observed a notable distinction between the Belt Sea and the Inner Baltic Sea sub-regions. Improved delineation of harbor porpoise population assignments for the Baltic based on genomic evidence is important for conservation management of this endangered cetacean in threatened habitats, particularly in the Baltic Sea proper. In addition, we show that SNPs outperform microsatellite markers and demonstrate the utility of RAD-tags from a relatively small, opportunistically sampled cetacean sample set for population diversity and divergence analysis.

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A simple discrimination method between Delphinidae and Phocoenidae based on the comparison of the intensity ratios of two band frequencies (130 and 70 kHz) is proposed. Biosonar signals were recorded at the Istanbul Strait (Bosphorus) in Turkey. Simultaneously, the presence of the species was confirmed by visual observation. Two types of thresholds of two-band intensity ratios, fixed and dynamic threshold, were tested for identification. The correct detection and false alarm rates for porpoises were 0.55 and 0.06 by using the fixed threshold and 0.74 and 0.08 by using the dynamic threshold, respectively. When the dynamic threshold was employed, the appropriate threshold changed depending on the mix ratio of recorded sounds from both Delphinidae and Phocoenidae. Even under biased mix ratios from 26% to 82%, the dynamic threshold worked with >0.80 correct detection and <0.20 false alarm rates, whereas the fixed threshold did not. The proposed method is simple but quantitative, which can be applicable for any broadband recording system, including a single hydrophone with two frequency band detectors.

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Despite no obvious barriers to gene flow in the marine realm, environmental variation and ecological specializations can lead to genetic differentiation in highly mobile predators. Here, we investigated the genetic structure of the harbour porpoise over the entire species distribution range in western Palearctic waters. Combined analyses of 10 microsatellite loci and a 5085 base-pair portion of the mitochondrial genome revealed the existence of three ecotypes, equally divergent at the mitochondrial genome, distributed in the Black Sea (BS), the European continental shelf waters, and a previously overlooked ecotype in the upwelling zones of Iberia and Mauritania. Historical demographic inferences using approximate Bayesian computation (ABC) suggest that these ecotypes diverged during the last glacial maximum (c. 23-19 kilo-years ago, kyrbp). ABC supports the hypothesis that the BS and upwelling ecotypes share a more recent common ancestor (c. 14 kyrbp) than either does with the European continental shelf ecotype (c. 28 kyrbp), suggesting they probably descended from the extinct populations that once inhabited the Mediterranean during the glacial and post-glacial period. We showed that the two Atlantic ecotypes established a narrow admixture zone in the Bay of Biscay during the last millennium, with highly asymmetric gene flow. This study highlights the impacts that climate change may have on the distribution and speciation process in pelagic predators and shows that allopatric divergence can occur in these highly mobile species and be a source of genetic diversity.

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Beach debris abundance was estimated from surveys on 10 beaches of the Turkish Western Black Sea Coast. Debris was collected from 20 m long transects during four different seasons; sorted and categorized by type, usage and origin. Litter density varied from 0.085 to 5.058 items m(-2). Debris was mainly composed of unidentifiable small size (2-7 cm) plastic pieces and beverage-related litter such as bottles and bottle caps. About half of the labeled litter was of foreign origin, including 25 different countries, 23% of which are in the Black Sea region. The south-western Black Sea Coast seems to receive foreign litter from two main sources: land-based debris from the neighboring countries and seaborne debris due to international shipping. Standardized methodology and indicators need to be designated all over the Black Sea basin in order to quantify and qualify coastal litter pollution, monitor compliance with MARPOL and develop regionally effective mitigation measures.

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Two major ecological transitions marked the history of the Black Sea after the last Ice Age. The first was the postglacial transition from a brackish-water to a marine ecosystem dominated by porpoises and dolphins once this basin was reconnected back to the Mediterranean Sea (ca. 8,000 y B.P.). The second occurred during the past decades, when overfishing and hunting activities brought these predators close to extinction, having a deep impact on the structure and dynamics of the ecosystem. Estimating the extent of this decimation is essential for characterizing this ecosystem's dynamics and for formulating restoration plans. However, this extent is poorly documented in historical records. We addressed this issue for one of the main Black Sea predators, the harbor porpoise, using a population genetics approach. Analyzing its genetic diversity using an approximate Bayesian computation approach, we show that only a demographic expansion (at most 5,000 y ago) followed by a contemporaneous population collapse can explain the observed genetic data. We demonstrate that both the postglacial settlement of harbor porpoises in the Black Sea and the recent anthropogenic activities have left a clear footprint on their genetic diversity. Specifically, we infer a strong population reduction (~90%) that occurred within the past 5 decades, which can therefore clearly be related to the recent massive killing of small cetaceans and to the continuing incidental catches in commercial fisheries. Our study thus provides a quantitative assessment of these demographically catastrophic events, also showing that two separate historical events can be inferred from contemporary genetic data.

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Recent climate change has triggered profound reorganization in northeast Atlantic ecosystems, with substantial impact on the distribution of marine assemblages from plankton to fishes. However, assessing the repercussions on apex marine predators remains a challenging issue, especially for pelagic species. In this study, we use Bayesian coalescent modelling of microsatellite variation to track the population demographic history of one of the smallest temperate cetaceans, the harbour porpoise (Phocoena phocoena) in European waters. Combining genetic inferences with palaeo-oceanographic and historical records provides strong evidence that populations of harbour porpoises have responded markedly to the recent climate-driven reorganization in the eastern North Atlantic food web. This response includes the isolation of porpoises in Iberian waters from those further north only approximately 300 years ago with a predominant northward migration, contemporaneous with the warming trend underway since the 'Little Ice Age' period and with the ongoing retreat of cold-water fishes from the Bay of Biscay. The extinction or exodus of harbour porpoises from the Mediterranean Sea (leaving an isolated relict population in the Black Sea) has lacked a coherent explanation. The present results suggest that the fragmentation of harbour distribution range in the Mediterranean Sea was triggered during the warm 'Mid-Holocene Optimum' period (approx. 5000 years ago), by the end of the post-glacial nutrient-rich 'Sapropel' conditions that prevailed before that time.

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BACKGROUND: Understanding the role of seascape in shaping genetic and demographic population structure is highly challenging for marine pelagic species such as cetaceans for which there is generally little evidence of what could effectively restrict their dispersal. In the present work, we applied a combination of recent individual-based landscape genetic approaches to investigate the population genetic structure of a highly mobile extensive range cetacean, the harbour porpoise in the eastern North Atlantic, with regards to oceanographic characteristics that could constrain its dispersal. RESULTS: Analyses of 10 microsatellite loci for 752 individuals revealed that most of the sampled range in the eastern North Atlantic behaves as a 'continuous' population that widely extends over thousands of kilometres with significant isolation by distance (IBD). However, strong barriers to gene flow were detected in the south-eastern part of the range. These barriers coincided with profound changes in environmental characteristics and isolated, on a relatively small scale, porpoises from Iberian waters and on a larger scale porpoises from the Black Sea. CONCLUSION: The presence of these barriers to gene flow that coincide with profound changes in oceanographic features, together with the spatial variation in IBD strength, provide for the first time strong evidence that physical processes have a major impact on the demographic and genetic structure of a cetacean. This genetic pattern further suggests habitat-related fragmentation of the porpoise range that is likely to intensify with predicted surface ocean warming.

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