Search

Understanding what environmental drivers influence marine predator-prey relationships can be key to managing and protecting ecosystems, especially in the face of future climate change risks. This is especially important in environments such as the Black Sea, where strong biogeochemical gradients can drive marine habitat partitioning and ecological interactions. We used underwater video recordings in the north-eastern Black Sea in November 2013 to observe the distribution and behaviour of the Black Sea sprat (Sprattus sprattus phalericus, Risso 1827) and its zooplankton prey. Video recordings have shown that the Black Sea sprat S. sprattus phalericus tolerates severely hypoxic waters near the redoxcline. The school was distributed in the 33-96 m layer [oxygen concentration (O2 ) 277-84 μmol L-1 ]. Some individuals were observed to leave the school and descended 20 m deeper for foraging on copepods in the 119-123 m layer (O2 12-10 μmol L-1 ). Zooplankton appeared concentrated on the upper boundary of the suboxic zone (O2

The paper presents characteristics of the species composition, spatial distribution, and trophic interactions of ichthyoplankton and zooplankton in the spring–summer period 2017 dependent on intensity of the warming-up of the upper sea layer against the background of transition in a system of the surface currents from the winter-to summer-type of the circulation. In April–May, successful spawning of temperate-water fish species was prolonged due to low values of the sea surface temperature (8–9°С) on the shelf of Crimean Peninsula between Kerch Strait and the cape Sarych. The maximum abundance of Sprattus sprattus eggs was 162.8 egg/m2 and larvae –116 ind/m2. Warm-water species occurred only in the western sector from Herakleian Peninsula to the Cape Tarkhankut, where the water temperature was at its maximum and peaked at 14–15°С. In June–July the delayed summer hydrological season hampered the warming-up of the upper quasi-homogenous layer, which thickness varied from 1–5 to 10–15 m. Notwithstanding the large number of species in the ichthyoplankton, maximum abundance did not exceed 50 egg/m2 and 14 ind/m2 for larvae. The proportion of larvae of temperate-water fish species averaged 32% and reached 40% in deep water areas. Juvenile stages of copepods of the cold-water complex were dominant in the larval fish diet both in the spring and summer seasons.

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.

The dynamics of glycogen recovery in the muscles and liver of the European flounder Plathichthys flesus (Linnaeus, 1758) and the European sprat Sprattus sprattus (Linnaeus, 1758) after exposure to trawl fishing has been studied. As the results show, the stress-inducing effect of fishing does not alter the glycogen content of the organs in the flounder, which leads a sedentary life, whereas a sharp decrease in glycogen is observed in the white and red muscles and the liver of the sprat, which is an actively swimming species. After capture, the dynamics of glycogen recovery in the organs of flounder has an undulatory pattern. The glycogen is completely restored within 12 h and is accompanied by a 100% survival rate of the flounder. The assumption is made that the resynthesis of glycogen in the organs of flounder occurs through the activation of carbohydrate metabolism in the liver. In sprat that had 3 h of “rest” after being caught and then placed in a 100‑liter tank to restore glycogen in tissues, a pronounced (4.5-fold) increase in the level of the polysaccharide was recorded from the white muscles, with a simultaneously low glycogen level in the liver. The glycogen compensation in the sprat possibly occurred through the reverse involvement of lactate in the polysaccharide resynthesis in the white muscles. The following additional 3-h period of rest was characterized by a significant (1.7-fold) decrease in the glycogen level in the white muscles compared to that in the previous rest period. No glycogen recovery in the sprat liver was observed throughout the entire rest period. Apparently, this organ is not involved in the polysaccharide recovery processes. The low survival rate of sprat (30%) is explained by the long exposure to stress caused by both capture and captivity in the tank, to which this “excitable” species is particularly sensitive.

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.

In the South Eastern Black Sea, anchovy (Engraulis encrasicolus), sprat (Sprattus sprattus), and horse mackerel (Trachurus mediterraneus) are the most important small pelagic fish both ecologically and economically. The stomach contents of 1485 fish, including anchovy, sprat, and horse mackerel, were examined. Fish fed on 35 prey taxa, and there were dietary differences among predators. Anchovies predominantly consumed calanoid copepods and bivalves; sprats had a diet dominated by calanoid copepods and Chaetognatha (Parasagitta setosa); horse mackerel consumed mainly decapods and calanoid copepods. Copepods in the stomachs of sprat were more abundant and more frequent than in the stomachs of anchovy or horse mackerel during all year. As the anchovies and horse mackerel grew, their copepod consumption increased, but despite their size, sprats consumed a similar amount of copepods. Seasonal shifts in diet were observed in all three species. In winter and autumn months, all small pelagic fish consumed copepod species. The bivalve larvae were mostly consumed in summer by anchovies (N%: 72.98) and in spring by sprats and horse mackerel (N%: 88.59 and 81.08, respectively). Decapod species were preferred in spring months by horse mackerel. P. setosa was mostly consumed in autumn and winter by sprat. Anchovy showed a low dietary overlap with sprat but had a high dietary overlap with horse mackerel. The feeding strategy of anchovy seems to be mixed, while horse mackerel is a generalist at the individual level, and sprat is a specialist at the population level.

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.

The different units in which the fatty acid profile can make it difficult to track the changes in eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid in canned fish. The influence of sterilization on EPA and DHA behavior and content in canned fish was investigated. Canned herring, mackerel, and sprats (in oil and tomato sauce) were examined. The canning process was not destructive on EPA and DHA as it has been believed so far. Losses of EPA and DHA in the whole canned food did not exceed 7.5%. Sterilization caused EPA and DHA to be “regrouped” from the fish to the sauce rather than their physical losses. After sterilization, the fish retained 64.8%–71.1% of EPA and DHA in relation to steamed fish, the rest of EPA and DHA passed to the sauce. Preference should be given to the production of canned food in which the liquid part is consumed. PRACTICAL APPLICATIONS: The presentation of EPA and DHA contents in % and in g/100 g (wet and dry matter) does not fully allow to track the changes in these acids in canned food. Only the analysis of EPA and DHA content in the whole canned food (in solid and liquid parts) allows to examine objectively the influence of sterilization on EPA and DHA content. This study unequivocally shown that the production process of canned fish is not as destructive on EPA and DHA as previously thought. It seems that changes in EPA and DHA content in fish during sterilization mainly depend on factors influencing the amount of cooking loss (lipid loses). However, preference should be given to the production of canned fish in which the liquid part is consumed rather than discarded.

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.

Fecundity of marine fish species is highly variable, but trade-offs between fecundity and egg quality have rarely been observed at the individual level. We investigated spatial differences in reproductive investment of individual European sprat Sprattus sprattus (Linnaeus 1758) females by determining batch fecundity, condition indices (somatic condition index and gonadosomatic index) as well as oocyte dry weight, protein content, lipid content, spawning batch energy content, and fatty acid composition. Sampling was conducted in five different spawning areas within the Baltic Sea between March and May 2012. Spawning sprat from the Kiel Bight were in a better nutritional condition compared to sprat from the Arkona Basin, Bornholm Basin, and the Gdansk Deep. These females were also producing up to twice as many oocytes, and invested significantly more energy in reproduction, than their counterparts sampled in the eastern part of the Baltic Sea. Still, oocytes produced by Kiel Bight sprat contained significantly lower fractions of the essential fatty acids 20:4 (n-6) and 22:6 (n-3). A seasonal trade-off between oocyte weight/lipid content and fecundity was found for Baltic sprat, albeit the gross energy invested into spawning remained constant. Observed spatial and seasonal differences in sprat reproductive investment may be linked to hydrographic conditions and food availability and will impact the survival probability of yolk-sac and first feeding larvae. These findings indicate that Baltic sprat is able to adapt its reproductive tactics to the highly variable pelagic habitat of the Baltic Sea.

This study was conducted on fresh and frozen-thawed sprat of the lowest utility, which is not used for consumption. The peptidase activity was measured (i) against acid- and base-hemoglobin (GPA) a...

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