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On February 27, 2018, a female smoothback angelshark, Squatina oculata, was incidentally captured in a gill-net fishery off the Mudanya coast (southeastern Sea of Marmara). An opportunistic photographic record confirmed the emergence of S. oculata in the Sea of Marmara, where its status in the area is considered questionable because of its absence for many years in the region. The current opportunistic records are valuable data sources, which can provide complementary information to fill the knowledge gaps in the life histories of rare, rarely caught, or endangered sharks and rays. [ABSTRACT FROM AUTHOR]

The commercially important Atlantic bluefin tuna (Thunnus thynnus), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts. Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean Sea and the Gulf of Mexico, with mixing occurring throughout the Atlantic. However, recent studies have challenged this assumption by revealing weak genetic differentiation and identifying a previously unknown spawning ground in the Slope Sea used by Atlantic bluefin tuna of uncertain origin. To further understand the current and past population structure and connectivity of Atlantic bluefin tuna, we have assembled a unique dataset including thousands of genome‐wide single‐nucleotide polymorphisms (SNPs) from 500 larvae, young of the year and spawning adult samples covering the three spawning grounds and including individuals of other Thunnus species. Our analyses support two weakly differentiated but demographically connected ancestral populations that interbreed in the Slope Sea. Moreover, we also identified signatures of introgression from albacore (Thunnus alalunga) into the Atlantic bluefin tuna genome, exhibiting varied frequencies across spawning areas, indicating strong gene flow from the Mediterranean Sea towards the Slope Sea. We hypothesize that the observed genetic differentiation may be attributed to increased gene flow caused by a recent intensification of westward migration by the eastern population, which could have implications for the genetic diversity and conservation of western populations. Future conservation efforts should consider these findings to address potential genetic homogenization in the species. [ABSTRACT FROM AUTHOR]

Across the Mediterranean and the Black Sea, an improvement in technological adoption which optimizes the environmental benefits of fisheries is needed. The testing of quality standards in trawl fishing is one of the essential components. In an experiment, we tested four bottom trawl cod-ends in the western Black Sea to determine the characteristics of the catch composition. Fishing trials were conducted by 40 mm diamond (40D), 44 mm diamond (44D), 40 mm square (the 40S), and 40 mm 90-degree turned (40T) mesh cod-ends for 31 bottom trawling hauls. The multivariate analysis of catch composition indicated a significantly higher differentiation between 40D and 40T cod-ends, mainly characterized by five species: Merlangius merlangus, Mytilus galloprovincialis, Trachinus draco, Mullus barbatus, and Uranuscopus scaber. The difference in the shape of cod-end meshes reflected the variation in the catchability and catch composition. However, the 40S and 40T showed 80% similarity in catch composition. Among cod-ends, 40T yielded in lowest catch per unit effort for both commercial and other species. Adoption of gear specially made to catch more target species can help bottom trawl fisheries further improve their ecological and economic sustainability. [ABSTRACT FROM AUTHOR]

Abnormalities of shape, color or body deformities such as lack of swim bladders or any parts of the body are an unexplained issue for many fish species. There is a gap of knowledge regarding their causes. Generally, it is an important problem in the rearing technique in aquaculture management due to the high economic consequences. The morphological abnormalities occur in marine fishes as well. Missing dorsal spines or rays, scale disorientation, jaw deformities, eye deformations and the lack of some parts of the body are within the context of abnormality. In the present study, the body abnormality observed in a specimen of European hake (Merluccius merluccius Linnaeus, 1758) missing its right eye which was caught by a fisherman in the Marmara Sea on 13 October 2020, and its causes are reported and discussed. Further studies are needed to correlate the wild fish anomalies caused by pollution. [ABSTRACT FROM AUTHOR]

This manuscript reports on four new jellyfish species in the Sea of Marmara (Turkey) (the scyphozoans Mawia benovici and Drymonema dalmatinum, hydrozoan Aequorea forskalea, and thaliacean Salpa maxima) based on plankton collections made in the years 2019-2021. This is the first record of Mawia benovici in both Turkish coastal areas and the Sea of Marmara. The jellyfish that was previously recorded as Drymonema sp. in the repetition Sea of Marmara was identified at the species level as D. dalmatinum. Furthermore, their possible introduction pathways are briefly discussed here. [ABSTRACT FROM AUTHOR]

The stock structure and productivity components (growth, maturity and mortality) of the Black Sea whiting Merlangius merlangus were studied in the western Black Sea for a year. The results aim to improve fisheries management of whiting in the Black Sea. Fresh samples were collected from commercial bottom trawlers between October 2017 and September 2018. Using monthly length-frequency data set for the growth trajectories, a bootstrapped procedure was employed to improve parameter optimization. Duration and timing of the spawning season and size at sexual maturity were modelled using generalized additive models (GAMs). The presence of clear differences in oocyte size groups indicates that oocyte development of Black Sea whiting is a 'group synchronous' ovarian developmental process characterized by continuous reproduction. From the gonadosomatic index values, their spawning activity intensifies especially between October and April, captured also in the time component in the GAM modelling. The length at first maturity was 13.9 cm for females and 12.5 cm for males. The mortality rates, yield per recruit analyses, and length-based indicators suggest that whiting is heavily exploited with alarming signs of overexploitation. Undoubtedly, setting catch limits and re-establishing management plans will be the first two steps to ensure reproductive success and prevent overfishing (F > Fmsy). [ABSTRACT FROM AUTHOR]

The genetic diversity of the Mediterranean swordfish (Xiphias gladius Linneus) has not been explored extensively at its easternmost range so far. In this study, modern X. gladius samples from the eastern part of the Mediterranean basin, north of the Aegean Sea (Aegean‐2013, n = 26) and the Mediterranean coast of Turkey (N.Levantine‐2013, n = 42) were studied genetically, along with ancient samples from Yenikapı excavation (n = 6). Partial mitochondrial DNA control region sequences (entire sequences, clade I and clade II) were evaluated spatially and temporally together with previously published sequences (Alvarado Bremer et al., Molecular Phylogenetics and Evolution, 2005, 36, 169–187; Viñas et al., ICES Journal of Marine Science, 2010, 67, 1222–1229; Righi et al., Diversity, 2020, 12, 170) from the rest of the Mediterranean Sea. Pair‐wise FST and pair‐wise AMOVA tests showed that, in general, groups of eastern populations and western Mediterranean populations have not genetically differed from each other significantly nearly in the past 20 years. Therefore, the results direct reconsideration of previous descriptions of population sub‐structure within the Mediterranean and support high gene flow throughout the region. On the contrary, the results of this study confirmed the existence of genetic diversity differences between western and eastern Mediterranean, with eastern being low. One‐tailed permutation tests revealed that θ, which is directly proportional to long‐term female effective population size (Ne), decreased significantly (P < 0.05) in both regions over the past two decades. On the Turkish coasts, θ is not significantly different from that of the nearly contemporary eastern Mediterranean population. Nonetheless, θ of the ancient sample was consistently and significantly (P < 0.001) higher than those of the eastern and western Mediterranean populations in clade I and clade II. Furthermore, it contains two mitochondrial haplotypes that are not observed in modern samples, suggesting that the Ne of X. gladius in the eastern was high in Byzantium times. Eight microsatellite loci were also genotyped in modern samples. The microsatellite‐based present Ne estimate of the pooled Aegean‐2013 and N.Levantine‐2013 populations was lower than 1000 according to the upper limit of 95% c.i. and possibly even lower than 100 according to the mean of posterior distribution of the present Ne estimate calculated by the software package MSVAR. These alarming genetic signals for the sustainability of X. gladius on the coasts of Turkey are in agreement with the nearly collapsing X. gladius fisheries as depicted also in the fisheries statistics. Overall, congruent with the previous studies, the data presented here show that sustainability of the X. gladius population in Mediterranean is under major threat. Therefore, X. gladius around the Turkish coasts need an immediate stringent action and management plan. [ABSTRACT FROM AUTHOR]