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The Baltic sprat Sprattus sprattus balticus is an important fishing species and takes the second place in abundance of the commercial catches after the Baltic herring in the eastern part of the Gulf of Finland. Before investigations of the sprat were rarely carried out in Leningradskaya region. Sprat is fished with the pelagic trawls as by-catch of the Baltic herring’s fishing clusters. The supply of the sprat forms in the western part of the Finnish Gulf and the Baltic Sea. This species goes to the eastern part of the gulf due to the forage migration. Materials for the research were the data obtained from the trawl fishery during the periods from January to May and from October to December 2017-2019 in Russian economic zone of the eastern part of the gulf close to the islands Bolshoy and Malyy Tyuters, Moshchnyy and Gogland. The analysis of the sprat distribution in 2019 was carried out based on the generalization of the results of trawl fishing. The review of the season fishing features in considered region is given. The amount of the catch of the species varied in the different fishing areas, changing significantly by months. The biggest catches reached 15-25 tons during 5 to 8 trawling hours were observed in November as well as in the former years. Largest number of the sprat was fished in the western border areas of the gulf which are adjacent to the Estonia and Finland waters.

The article deals with the research aimed at developing an enzymatic method for removing the subcutaneous fat in the technology of fish snacks production. Currently, fish snacks are popular among consumers. However, due to fierce market competition, the priority is to develop new raw materials, improve the taste characteristics of snacks and increase the shelf life of finished products. The most common commercial fish species of Ukraine caught in sufficient quantities are Black Sea sprat (Sprattus sprattus) and European anchovy (Engraulis encrasicolus). The main problem in the production of quality snack products is the high fat content in these raw materials. Oxidation of the subcutaneous layer of fat leads to an unpleasant odor and taste, and as a result – reduction of the shelf life of the product. One possible way to solve these problems is to remove lipids using biotechnology. Experiments how to solve the problem of removing the subcutaneous fat using a biotechnological method of processing are described in this work. The process of the subcutaneous fat removing has been performed using a complex of plant lipolytic enzymes extracted from wheat bran. The change in the mass fraction of fat in fish raw materials depending on the duration of the fermentation process under the action of wheat bran lipase has been studied. Results of the research showed, that the mass fraction of Black Sea sprat fat under the action of a complex of wheat bran enzymes had decreased from 12 to 4.5 %. The optimal temperature of the complex of lipolytic enzymes of wheat bran has been determined. The hydrolysis of fat is almost nonexistent at the temperature range from 0 up to 5 °C. The greatest activity of enzymes is observed at a temperature of 25… 35 °C and within 30 min of hydrolysis 7… 8 % of fat is being removed. The optimal pH value for enzymatic degreasing has been investigated. It has been found that the fastest breakdown of fat occurs at pH values from 7 to 8 and is 7… 8 % of fat in 30 minutes. Based on the research results, a technological scheme for the production of fish snacks has been developed.

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.

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.

Environmental conditions of mammalian juveniles may have delayed effects on their life histories and fitness, such as body size or reproductive rate later in their lives. In the present study, we tested this hypothesis on Baltic grey seals (Halichoerus grypus) and examined (1) the possible effects of prey fish quality and winter temperature on body condition of grey seal pups of both sexes and (2) the possible delayed impacts of pup environment on the body size and birth rate of adult grey seals. Body condition (blubber thickness) of especially female pups in April–May correlated negatively with winter temperatures, and body condition of male pups correlated positively with prey fish quality (herring Clupea harengus and sprat Sprattus sprattus weight). Males reached the asymptotic length at the age of 10.3 years, and body length of adult males (≥ 10 years old) was positively related to herring and sprat weight in their birth year. Females reached the asymptotic length at the age of 5.9 years. Birth rate of females (age 7–24 years) was negatively related to winter temperature in their birth year. We conclude that both changes in prey fish quality and climate may affect body condition of pups and thus also cause delayed effects on adult fitness: body size and reproductive rate of Baltic grey seals.

Reproductive rate of grey seal (Halichoerus grypus) females has fluctuated during the 2000s, although reproductive disturbances, which occurred earlier, are rare at present. Here we aimed to study especially the food web factors possibly affecting the birth rate of Baltic grey seals and whether birth rate can be used as an indicator of the changes in the Baltic food web. Our results showed that the birth rate of grey seals was significantly related to herring (Clupea harengus membras) and sprat (Sprattus sprattus) quality (weight) which, in turn were influenced by sprat and cod (Gadus morhua) abundance, as well as zooplankton biomass and plankter size. This suggests strong trophic coupling over three trophic levels. We thus conclude that the birth rate of grey seals can be used as an indicator of the status of the Baltic food web. Based on this, we suggest a threshold value for good food web status for a stable, non-growing seal population. Highlights • Birth rate of grey seals was related to changes in the quality of clupeids. • The quality of clupeids reflected changes in the Baltic food web. • Birth rate can thus be used as an indicator of the status of the Baltic food web. • Different threshold values of birth rate for a growing and stable seal population should be determined.

Long-term datasets developed based on measurements of archived fish otoliths may help in the evaluation of climatic impacts on marine resources. The objective of the present study was to identify the factors that influence interannual variations in the somatic growth rate of herring (Clupea harengus) in the Baltic Sea. This work covers otolith samples collected from commercial catches and during scientific surveys from 1951 to 2017 in the Polish zone of the southern part of the Baltic. Otolith increment widths, which represent changes in fish growth, were analyzed with linear mixed models to investigate different intrinsic and extrinsic sources of fish growth variation. The stock biomass of pelagic species (herring and sprat Sprattus sprattus), sea surface temperature, Baltic Sea Index and land precipitation over the catchment area were considered potential predictors of herring growth. Methods to identify the optimal time window for environmental factors were incorporated in the modeling. Moreover, a wavelet coherence analysis, tests for identification of regime shifts in fish growth and a spatial correlation analysis were applied to the data. The developed multidecadal otolith-based biochronology showed that the growth of Baltic herring is under the strong influence of interspecific competition between herring and sprat, but the biochronology also indicated a high correlation with precipitation patterns over the runoff area and hydrological conditions within the Baltic Sea. A detailed investigation revealed that the relationships between herring growth and abiotic conditions or other ecosystem components can vary over time. The recognized complex ecological effects on herring growth necessitate the application of holistic ecosystem-based approaches for sustainable management and exploitation of small pelagic fish resources.

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.

WOS:000744169400004; International audience; Data on Sardinella aurita (round sardinella) and Sprattus sprattus (European sprat) in the Mediterranean Sea are limited due to their scarce commercial interest, at least in European countries. Yet, these two small pelagic fish, sitting at opposite ends of the thermal range, could be interesting sentinel species to monitor the effects of climate change in the basin. Using the Mediterranean International Acoustic Surveys (MEDIAS) - the most extensive source of information on these species - we analysed their biomass in several geographical subareas of the central and western Mediterranean Sea in relation to satellite-derived environmental parameters. Our findings highlight that the S. aurita biomass responded to temperature, salinity, chlorophyll concentration and sea level anomaly, depending on the GSA examined, whereas the S. sprattus biomass correlated significantly with salinity in GSA 6, with salinity and chlorophyll concentration in GSA 7 and with sea level anomaly in GSA 17. These data widen our knowledge of the factors that contribute to the ecology of these species. Further studies of their spatial distribution and of their interactions with other small pelagic species, predators and prey are needed to depict a more comprehensive scenario.

Studies of the diet, feeding habits and trophic activity of top marine predators are essential for understanding their trophodynamics. The main direct method used for such studies thus far has been morphological inventories of stomach contents. This approach presents limitations such as missing gelatinous prey, which are usually digested too quickly to be detectable. Here, we analysed the stomachs of 48 Atlantic bluefin tuna (Thunnus thynnus, approximately 15 to 60 kg, including juveniles and adult fishes) collected from the Mediterranean Sea through the metabarcoding of two gene regions (cytochrome c oxidase subunit I (COI) and the ribosomal 18S-V1V2 region). The identified prey taxa and their relative read abundances (RRAs) estimated using COI results were in line with the findings of morphologically based inventories simultaneously performed on the same set of tuna samples. In both cases (and with the same rankings), the prey taxa included anchovy (Engraulis encrasicolus, here detected in more than 80% of samples, RRA = 43%), sardine (Sardina pilchardus, also approximately 80%, RRA = 30%), sprat (Sprattus sprattus, approximately 66%, RRA = 8%), mackerel (Scomber colias, approximately 44%, RRA = 7%) and cephalopods (approximately 15%, RRA = 1.4%). Another striking result was the detection, based on 18S (with which vertebrates were detected as the most abundant group, RRA = 61.6%), of a high prevalence and diversity of gelatinous organisms (RRA = 27.1%), including cnidarians (6.7%), salps (11.7%), and ctenophores (8.7%), the latter increasing with the size of the predator. These results thus support the hypothesis of the role of gelatinous prey in the diet of Atlantic bluefin tuna, suggesting that this species is even more generalist and opportunistic than previously thought. This study further confirms that DNA metabarcoding can be a powerful tool for assessing the diet and trophodynamics of top marine predators.

Thiamine (vitamin B1) deficiency of salmonines, caused by an abundant lipid-rich fish diet and consequently, the abundance of polyunsaturated fatty acids, is called the M74 syndrome in the Baltic Sea. Because of its deleterious effects on wild Atlantic salmon (Salmo salar) stocks and progeny production in fish cultivation, a model was developed to derive the annual female-specific mortality percentages of yolk-sac fry (YSFM) from the free thiamine concentrations of unfertilized eggs. In years with a high M74 incidence, thiamine-deficient females were larger, with a larger condition factor (CF) than non-M74 females. Otherwise, M74 females were generally smaller. The mean CF of M74 females was in most years higher than that of non-M74 females. The model compiled enables the cost-effective estimation of YSFM of individual female salmon, without the incubation of eggs and hatched yolk-sac fry for several months, thus benefitting the management of salmon stocks and their efficient utilization.

Small- and intermediate-size pelagic fisheries are highly impacted by environmental variability and climate change. Their wide geographical distribution and high mobility makes them more likely to shift their distribution under climate change. Here, we explore the potential impact of different climate change scenarios on the four main commercial pelagic species in the North-East Atlantic (NEA): Atlantic mackerel (Scomber scombrus), European sprat (Sprattus sprattus), Atlantic herring (Clupea harengus) and blue whiting (Micromesistius poutassou). We used a process-based fisheries model (SS-DBEM), where all the target species were exploited at their maximum sustainable yield (MSY), to project future potential catches under a high- and low-future-greenhouse-gas scenario (RCP 2.6 and 8.5, respectively). Two ocean biogeochemical models (GDFL and MEDUSA) were used to force the environmental conditions. Mackerel and sprat are projected to have increases in a potential catch under both scenarios. Herring and blue whiting are projected to increase under the RCP2.6, but future projections under RCP8.5 show mixed responses with decreases or no changes forecasted. Overall, the potential catch is projected to increase in the northern area of the NEA but is projected to decrease in the southern area. These projected changes are mainly driven by changes in temperature and primary production. Shifts in the distribution of pelagic resources may destabilize existing international agreements on sharing of straddling resources as exemplified by the dispute in sharing of quota for Atlantic mackerel. Novel climate-ready policy approaches considering full species distribution are needed to complement current stock-based approaches.

The drivers of recruitment of selected Baltic sprat (Sprattus sprattus) and herring (Clupea harengus) stocks were investigated. Data on the interaction dynamics among fish species, the biological characteristics of the stocks, the biomass of the main predators, and the hydroclimatic environmental factors (Baltic Sea Index and sea surface temperature) were used in the analysis. The combination of random forest (Boruta algorithm) and “sliding window” approaches was tested on the simulated data and then used for the selection of relevant predictors and the optimal time window for real environmental variables. Sea surface temperature had a significant positive effect on the recruitment processes. Moreover, contrasting effects were observed in the mean Baltic Sea Index from two different time windows. The same environmental variable generated contrasting short-term and long-term effects on fish recruitment. This paper highlights the potential benefits of random forest and data mining applications for the incorporation of environmental factors in the assessment of stocks. The proposed analytical approach may be valuable for the investigations of complex environmental impacts in a broad range of ecological studies.

The purpose of this study was to investigate comparatively the sprat (Sprattus sprattus) fisheries in the whole of the Black Sea and in the Turkish coast of the Black Sea. With this aim, the prior studies on the sprat fisheries conducted from 1970 to recent years in the Black Sea and Turkish coast of Turkey were examined. Especially changes in annual catch amounts and on likely reasons were focused. As a result of evaluating the obtained data, necessary precautions for sustainable fisheries were determined and solution proposals have been presented. Sprat is the second most caught fish species in recent years and an important raw material resource for fish flour and fish oil industry. Especially in the Samsun coast of Turkey, this is target species for commercial pelagic trawl fisheries. Sprat has been caught by Georgia, Russia Federation, Ukraine, Romania and Bulgaria from the Black Sea since the beginning of 1970s. In Turkey, the first sprat fishing started in 1993 and increased gradually until 2007. Sprat catch increased rapidly from 2008 to 2011 and reached 87.141 tons in 2011 after which a sharp decline occurred (12.092 tons in 2012 and 9.764 tons in 2013). Then, it increased again and reached 41.648 tons in 2014 and 76.996 tons in 2015. Trend of annual catch values showed that there is no stability in the stock of this species in Turkish waters of the Black Sea.

A successful discrimination of fish populations is essential for sustainable management and assessment. Otolith shape analysis has been used on several species to reveal their population structure. Our aim was to use the otolith shape of European sprat (Sprattus sprattus) to investigate large- and small-scale geographical variability across the Greater North Sea ecoregion. The otolith shape was extracted from digitalised images and transformed into Wavelet coefficients to be analysed with multivariate statistics. Otolith shape was observed to follow the genetic population structure recently defined for the region, supporting the latest revision of the stock boundaries. Four main groups were identified based on phenotypic variability: (i) Norwegian fjords; (ii) North Sea and offshore Skagerrak–Kattegat; (iii) coastal Skagerrak–Kattegat; and (iv) Uddevalla fjord. However, 4-fold cross-validations based on Linear Discriminant Analysis resulted in low accuracy limiting at the moment the ability to use otolith shape analysis for population identification at an operational basis. Our results show the importance of coastal areas, which might be inhabited by distinct populations of sprat that are currently not acknowledged in the management and assessment. publishedVersion

This study aims to calculate the age, growth, and mortality rate of commercially important fish species, namely Engraulis encrasicolus, Trachurus mediterraneus, Sprattus sprattus, Merlangius merlangus, and Mullus barbatus, in the southeastern Black Sea between 2008 and 2011. These species are commercially important for Turkish and other riparian country fisheries. The samplings were carried out using bottom trawls, purse seines and various gillnets. Length-weight, age-length, the Von Bertalanffy equation, total mortality rate (Z), natural mortality rate (M), fishing mortality rate (F), and exploitation rate (E) were estimated for each species to use in further population analyses and stock assessments research. Additionally, the results of this study were evaluated considering the “ Task Group 3 Report-Commercially Exploited Fish and Shellfish ” in the Marine Strategy Framework Directive (MSFD) published by the European Commission (2008/56/EC).

Summary Although many marine ecosystems have been adversely impacted by human activities,1 some are now recovering due to reductions in fishing pressure.2–4 Here, we document the recovery of an ecosystem subjected to intense anthropogenic activity for over 200 years, the Clyde Sea.5 This region once had productive fisheries for herring (Clupea harengus) and other fish, but these disappeared at the turn of the century.6,7 Using acoustic surveys of the pelagic ecosystem, we found that the Clyde Sea supports 100 times as many forage fish as in the late 1980s. However, herring has now been replaced by sprat (Sprattus sprattus), despite virtually no fishing on herring for 20 years. A combination of a warming sea,6 bycatch of herring in the prawn (Nephrops norvegicus) fishery,8,9 and susceptibility of herring to poor recruitment may have contributed to this unexpected recovery. We compare this to similar unexpected "recoveries" involving unforeseen ecosystem effects, such as the return of hake (Merluccius merluccius) to the North Sea;10,11 the recent expansion of the pelagic squat lobster, "munida," (Pleuroncodes monodon) off Peru;12 and the increase in scallop (Placopecten magellanicus) numbers on Georges Bank.13 The lack of a current sprat fishery in the Clyde presents a unique opportunity to develop an alternative industry for its seafaring community: ecotourism. Charismatic megafauna (whales, dolphins, and seabirds) that people will pay to see14 will, in time—if not already15,16—be drawn in by the abundance of forage fish now present, further restoring the biodiversity of the region after centuries of overexploitation.

Information about species interactions at a spatial scale comparable to the perceptive abilities of the involved species is crucial for establishment of predictive food consumption models at the population level. Nevertheless, such information is sparse due to methodological constraints. We studied the diel vertical dynamics of species interactions between Atlantic cod Gadus morhua and its major clupeid prey, sprat Sprattus sprattus, at a location in the Bornholm Basin of the central Baltic Sea during late winter. This was accomplished by combining acoustic information on diel vertical fish distribution, time of ingestion of individual sprat estimated from cod stomach content data and observed vertical profiles of salinity, temperature and oxygen content. Predationby cod took place primarily at dusk and dawn during ascent and descent of sprat associated with school dissolution and formation, respectively. Cod resided close to the bottom outside these temporal predation windows. Sprat schools were located at the same depth as cod in the daylight hours, whereas at night dispersed sprat were situated higher in the water column. These verticaldynamics could be explained by fitness optimization using bioenergetics and trade-offs between temperature, oxygen saturation of the water and predation risk. This study forms a first step towards providing a mechanistic background for the predatory impact of cod at the basin scale and beyond

Fatty acids (FAs) were analysed in Baltic herring (Clupea harengus membras) stored in the Swedish Environmental Specimen Bank for up to 40 years. The purpose was to evaluate the retrospective use of FA signatures to detect temporal and spatial changes in the Baltic ecosystem. Fish from northern and central Baltic captured in the 1970s, the 1980s, in 1990, 2000, and 2009 and stored at − 25 °C were analysed. From the 1980s and onward herring from the south Baltic were included. A total of 55 FA and 4 alkenyl chains (detected as dimethyl acetals) were identified, and 28 of these (present at > 0.5% by weight) were used in evaluation of the data. The amount of some 20–22 carbon polyunsaturated fatty acids (PUFA) was related to time with lower amounts in older samples while other PUFAs were not related to time. Principal component analysis with saturated FAs and monounsaturated FAs showed similar sample groupings as the one obtained by including the PUFAs. The differences found in herring FA in this longitudinal study could be attributed to location of sampling, year of collection and storage time. However, the clearly distinguishable pattern in the FA composition in herrings from different locations in the Baltic Sea seen at all decades indicate that this technique can be used retrospectively.

International audience; Recently, the abundance of young Atlantic bluefin tuna (Thunnus thynnus) tripled in the northwestern Mediterranean following effective management measures. We investigated whether its predation on sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) could explain their concurrent size and biomass decline, which caused a fishery crisis. Combining the observed diet composition of bluefin tuna, their modelled daily energy requirements, their population size, and the abundance of prey species in the area, we calculated the proportion of the prey populations that were consumed by bluefin tuna annually over 2011-2013. To assess whether tuna could alter the size structure of the three small pelagic fish populations (anchovy, sardine, and sprat (Sprattus sprattus)), the size distributions of the consumed prey species were compared with those of the wild populations. We estimated that the annual consumption of small pelagic fish by bluefin tuna is less than 2% of the abundance of these populations. Furthermore, size selectivity patterns were not observed. We thus concluded that tuna predation is unlikely to be the main cause of major changes in the small pelagic fish populations from this area.

In this paper, maximum sustainable yield (MSY) parameters for the Baltic Sea sprat (Sprattus sprattus) are estimated in relation to pressure from cod (Gadus morhua) predation and the influence of density dependence on sprat growth. This study is based on long-term deterministic and stochastic simulations in which sprat density-dependent growth and predation mortality are considered. The resultant model is a relatively simple tool that allows for streamlined analyses of problems typically approached using complex multispecies models. The analysis indicates that estimates of the MSY parameters (i.e., MSY and FMSY) and equilibrium biomass differ significantly between approaches that hold growth and natural mortality constant and those that allow for density-dependent growth and natural mortality. Based on the cod biomass observed in the 1980s, the MSY parameters estimated by a model that accounts for density-dependent growth and by a model assuming constant growth may differ by a factor of 2. As such, the MSY parameters decline (approximately linearly) with the size of the cod stock.

Predation on cod (Gadus morhua) eggs by sprat (Sprattus sprattus) and herring (Clupea harengus) is known to be one of the processes influencing reproductive success of the eastern Baltic cod and has been reported to have contributed to lack of recovery of the stock in the 1990s. This study quantifies the predation on cod eggs in the Bornholm Basin, the major spawning area of cod in the central Baltic Sea, in the 1990s in comparison with the second half of the 2000s. The analyses involve estimating daily consumption rates of predator populations, which are then compared with corresponding daily egg production rates. As a methodological advancement compared with earlier studies, spatially resolved information on predator distribution and abundance is utilized in quantifying predator stock size. This resulted in more realistic consumption estimates in relation to overall egg production compared with earlier studies that consistently overestimated predation pressure by clupeids. Our results suggest a generally lower predation pressure on cod eggs in the mid- to late 2000s, due to a combination of reduced predator abundance and lower daily rations by individual predators.

Food-web indicators for marine management are required to describe the functioning and structure of marine food-webs. In Europe, the Marine Strategy Framework Directive (MSFD), intended to lead to a 'good environmental status' of the marine waters, requires indicators of the status of the marine environment that also respond to manageable anthropogenic pressures. Identifying such relationships to pressures is particularly challenging for food-web indicators, as they need to be disentangled from linkages between indicators of different functional groups caused by species interactions. Still, such linkages have not been handled in the indicator development. Here we used multivariate autoregressive time series models to identify how fish indicators in an exploited food-web relate to fishing, climate and eutrophication, while accounting for the linkages between indicators caused by species interactions. We assembled 31-year long time series of indicators of key functional groups of fish in the Central Baltic Sea pelagic food-web, which is characterized by strong trophic links between cod (Gadus morhua) and its main fish prey sprat (Sprattus sprattus) and herring (Clupea harengus). These food-web indicators were either abundance-based indicators of key piscivores (cod) and zooplanktivores (sprat and herring) or size-based indicators of the corresponding trophic groups (biomass of large predatory fish (cod >= 38 cm) and biomass of small prey fish (sprat and herring

The Mediterranean Sea is classified as a “data-poor” region in fisheries due to its low number of assessed stocks given its biodiversity and number of exploited species. In this study, the CMSY method was applied to assess the status and exploitation levels of 54 commercial fish and invertebrate stocks belonging to 34 species fished by Turkish fleets in the Eastern Mediterranean (Levantine) and Black Seas, by using catch data and resilience indices. Most of these marine taxa currently lack formal stock assessments. The CMSY method uses a surplus production model (SPM), based on official catch statistics and an abundance index derived from scientific surveys. The SPM estimates maximum sustainable yield (MSY), fishing mortality (F), biomass (B), fishing mortality to achieve sustainable catches (Fmsy), and the biomass to support sustainable catches (Bmsy). Our results show the estimated biomass values for 94% of the stocks were lower than the required amount to support sustainable fisheries (Bmsy). Of the 54 stocks, 85% of them can be deemed as overfished; two stocks were not subject to overfishing (Sardina pilchardus and Trachurus mediterraneus in the Marmara Sea) while only one stock (Sprattus sprattus in the Black Sea) is healthy and capable of producing MSY. Annual values of the stock status indicators, F/Fmsy and B/Bmsy, had opposing trends in all regions, suggesting higher stock biomasses could only be achieved if fishing mortality is drastically reduced. Recovery times and levels were then explored under four varying F/Fmsy scenarios. Under the best-case scenario (i.e., F = 0.5Fmsy), over 60% of the stocks could be rebuilt by 2032. By contrast, if normal fishing practices continue as usual, all stocks will soon be depleted [if not already] (F = 0.95Fmsy), whose recover may be impossible at later dates. The results of this study are supported by previous regional assessments confirming the overexploitation of Turkish fisheries is driving the near-total collapse of these marine wild fisheries. Hence, the need to urgently rebuild Turkey’s marine fisheries ought to be prioritized to ensure their future viability.

To establish if fishes’ consumption of jellyfish changes through the year, we conducted a molecular gut‐content assessment on opportunistically sampled species from the Celtic Sea in October and compared these with samples previously collected in February and March from the Irish Sea. Mackerel Scomber scombrus were found to feed on hydrozoan jellyfish relatively frequently in autumn, with rare consumption also detected in sardine Sardina pilchardus and sprat Sprattus sprattus. By October, moon jellyfish Aurelia aurita appeared to have escaped predation, potentially through somatic growth and the development of stinging tentacles. This is in contrast with sampling in February and March where A. aurita ephyrae were heavily preyed upon. No significant change in predation rate was observed in S. sprattus, but jellyfish predation by S. scombrus feeding in autumn was significantly higher than that seen during winter. This increase in consumption appears to be driven by the consumption of different, smaller jellyfish species than were targeted during the winter.

The genus Sprattus comprises five species of marine pelagic fishes distributed worldwide in antitropical, temperate waters. Their distribution suggests an ancient origin during a cold period of the earth’s history. In this study, we evaluated this hypothesis and corroborated the non-monophyly of the genus Sprattus, using a phylogenetic approach based on DNA sequences of five mitochondrial genome regions. Sprattus sprattus is more closely related to members of the genus Clupea than to other Sprattus species. We also investigated the historical biogeography of the genus, with the phylogenetic tree showing two well-supported clades corresponding to the species distribution in each hemisphere. Time-calibrated phylogenetic analyses showed that an ancient divergence between Northern and Southern Hemispheres occurred at 55.8 MYBP, followed by a diversification in the Oligocene epoch in the Northern Hemisphere clade (33.8 MYBP) and a more recent diversification in the Southern Hemisphere clade (34.2 MYBP). Historical biogeography analyses indicated that the most recent common ancestor (MRCA) likely inhabited the Atlantic Ocean in the Southern Hemisphere. These results suggest that the ancestral population of the MRCA diverged in two populations, one was dispersed to the Northern Hemisphere and the other across the Southern Hemisphere. Given that the Eocene was the warmest epoch since the Paleogene, the ancestral populations would have crossed the tropics through deeper cooler waters, as proposed by the isothermal submergence hypothesis. The non-monophyly confirmed for the genus Sprattus indicates that its systematics should be re-evaluated.

We addressed the behavioral patterns and DVM dynamics of sprat overwintering in a Norwegian fjord (150 m) with increasing hypoxia by depth. An upward-facing echosounder deployed at the bottom and cabled to shore provided 4 months of continuous acoustic data. This enabled detailed studies of individual behavior, specifically allowing assessment of individual vertical migrations at dusk and dawn in relation to light, analysis of so-called rise-and-sink swimming, and investigation of the sprat’ swimming activity and behavior in severely hypoxic waters. Field campaigns supplemented the acoustic studies. The acoustic records showed that the main habitat for sprat was the upper ∼65 m where oxygen concentrations were ⩾0.7 mL O 2 L −1 . The sprat schooled at ∼50 m during daytime and initiated an upward migration about 1 h prior to sunset. While some sprat migrated to surface waters, other individuals interrupted the ascent when at ∼20–30 m, and returned to deeper waters ∼20–50 min after sunset. Sprat at depth was on average larger, yet individuals made excursions to- and from upper layers. Sprat were swimming in a “rise and sink” pattern at depth, likely related to negative buoyancy. Short-term dives into waters with less than 0.45 mL O 2 L −1 were interpreted as feeding forays for abundant overwintering Calanus spp. The deep group of sprat initiated a dawn ascent less than 1 h before sunrise, ending at 20–30 m where they formed schools. They subsequently returned to deeper waters about ∼20 min prior to sunrise. Measurements of surface light intensities indicated that the sprat experienced lower light levels in upper waters at dawn than at dusk. The vertical swimming speed varied significantly between the behavioral tasks. The mixed DVM patterns and dynamic nocturnal behavior of sprat persisted throughout winter, likely shaped by individual strategies involving optimized feeding and predator avoidance, as well as relating to temperature, hypoxia and negative buoyancy.