Coordinated gas release among the physostomous fish sprat (Sprattus sprattus)

Previous experimental studies suggest that the production of sound associated with expelling gas from an open swimbladder may play a role in communication. This would suggest non-random gas release. We used deployed echosounders to study patterns of gas release among a fjord population of sprat (Sprattus sprattus). The echosounder records concurrently revealed individual fish and their release of gas. The gas release primarily occurred at night, partly following recurrent temporal patterns, but also varying between nights. In testing for non-randomness, we formulated a data-driven simulation approach. Non-random gas release scaled with the length of the analyzed time intervals from 1 min to 6 h, and above 30 min the release events in more than 50% of the intervals were significantly connected.

Ихтиологические исследования на НИС «Профессор Водяницкий» у побережья Крыма и в районе Филлофорного поля Зернова в осенний период (2010 г.) и некоторые новые сведения об ихтиофауне Чёрного моря

После длительного периода отсутствия ихтиологических исследований на научноисследовательских судах Института биологии южных морей имени А.О. Ковалевского в Чёрном море (за исключением ихтиопланктонных съемок и прибрежных ловов на фелюге) они были проведены в 68-м рейсе НИС «Профессор Водяницкий» осенью 2010 г. Особый интерес представляют ихтиологические наблюдения в районе ботанического заказника Филлофорного поля Зернова, где аналогичные работы не проводились уже несколько десятков лет. В исследованиях были использованы удебные ловы, визуальные наблюдения и случайные поимки рыб. Впервые в этом Филлофорном поле поймана присоска пятнистая Diplecogaster bimaculata (Bonnaterre, 1788) на столь далеком расстоянии от берега, но при этом на глубине обычной для обитания вида. По современном видовому составу рыб Филлофорное поле Зернова можно охарактеризовать как относительно бедный район северо-западной части Чёрного моря. Трофическая цепь рыб представлена следующим образом: шпрот Sprattus sprattus (Linnaeus, 1758)→мерланг Merlangius merlangus (Linnaeus, 1758)→катран Squalus acanthias Linnaeus, 1758. В ихтиоцен поля Зернова входят как стайные пелагические виды – ставрида Trachurus mediterraneus (Steindachner, 1868), шпрот, так и придонные – мерланг, присоска. По сборам в этом районе уточнены максимальные размеры самцов черноморского мерланга – 18,8 см в эконом зонах бывшего СССР. В районе Батилимана отмечена самая глубоководная поимка морского конька Hippocampus hippocampus (Linnaeus, 1758) в Чёрном море.

Genetic population structure and tools for the management of European sprat (Sprattus sprattus)

This study used RAD-seq-derived SNPs to explore population connectivity, local adaptation, and individual assignment in European sprat (Sprattus sprattus) and inform the alignment of management units with biological processes. FST, clustering, and outlier analyses support a genetically cohesive population spanning the Celtic Sea-English Channel-North Sea-Kattegat (NE Atlantic) region. The lack of structure among the NE Atlantic samples indicates connectivity across current management boundaries. However, the assumption of demographic panmixia is cautioned against unless verified by a multidisciplinary approach. The data confirm high genetic divergence of a Baltic population (average FST vs. NE Atlantic samples = 0.051) with signatures compatible with local adaptation in the form of outlier loci, some of which are shown to occur within exonic regions. The outliers permit diagnostic assignment of individuals between the NE Atlantic and Baltic populations and thus represent a “reduced panel” of markers for monitoring a potential mixed stock fishery within the western Baltic. Overall, this study provides information that may help refine spatial management boundaries of sprat and resources for genetic-assisted management.

Modern state of the reproductive potential of Black Sea sprat Sprattus sprattus phalericus (Risso, 1826) (Pisces: Clupeidae) in Crimean region and conditions for its formation

Black Sea sprat Sprattus sprattus phalericus (Risso, 1826) is one of the abundant species of fish in the Sea of Azov – Black Sea basin. Due to its large number sprat plays an extremely important role in the ecosystem of the sea, being an intermediate link between zooplankton and representatives of the highest trophic level – large predatory fish, dolphins, and birds. At the same time sprat is one of the important commercial fish in all the Black Sea countries, steadily being on the second place of catch volume in recent decades (after anchovy). The total catch reaches 100 thousand tons. Turkey and Ukraine are the main producing countries. Monitoring and forecast of biological state of sprat population with rising fishing intensity and climate changes are urgent tasks. The research subject of this article is the long-term (2000–2016) dynamics of biological (qualitative) parameters determining the population fecundity of Black Sea sprat in Crimean region, the current state of reproductive potential, and the conditions for its formation. The article is based on the results of own research. Parameters determining the population fecundity – the length-age structure of the spawning part population, the absolute individual fecundity, and the sex structure population (ratio between females and males) – were studied. In the long-term plan (in 2011–2016 compared with 2000–2004) the average length of spawning females decreased by 1.22 times (from 7.36 to 6.03 cm). It was accompanied by a decrease in the absolute individual fecundity by 2.39 times (from 13 625 to 5690 eggs). The numerical ratio between females and males decreased by 1.23 times (from 1.95 to 1.59). Simultaneously the sprat stock in the northern part of the Black Sea was reduced by more than 2.5 times (from > 500 thousand tons to < 200 thousand tons). As a result, the population fecundity of sprat in Crimean region decreased by more than 7 times (2.39 × 1.23 × 2.5). The conditions of sprat fishing in the northern part of the Black Sea (from the mouth of the Danube River to the Kerch Strait) were studied. They showed 2-fold decrease (from 251.9 thousand tons in 2000–2004 to 129.1 thousand tons in 2011–2016) in the total catch and more than 2.3-fold decrease (from 50.4 to 21.4 thousand tons) in average annual catch in this region. On the contrary, in the Crimean shelf the total catch at that time increased by 1.2 times (from 76.9 to 92.2 thousand tons), and its average annual value remained constant (15.4 thousand tons). While reducing the stock by 2.5 times, this means that the fishing pressure on the Crimean population increased 2.5 times. This fact suggests considering the factor of fishing as the main cause of its degradation. Validity of this version is confirmed by the fact of conjugacy (inverse connection) of interannual fluctuations between the catch and the length-age parameters of sprat in Crimean region in 2003–2013 previously found: catches over 15–16 thousand tons were accompanied by a next year decrease in the fish average length. Regulation of fishing is a necessary condition for preventing further degradation, for restoring and maintaining sustainable state of sprat population in Crimean region and its reproductive potential. The negative impact of natural (climatic and trophic) factors on the state of the population should be recognized as a secondary one. Local overfishing indicates indirectly the structuring of the commercial stock of Black Sea sprat, its division into a number of geographical aggregations (stock units), i. e. the presence of intraspecific differentiation.