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  • 1.
    Florin, Ann-Britt
    et al.
    Fiskeriverkets kustlaboratorium.
    Bergström, Ulf
    Fiskeriverkets kustlaboratorium.
    Ustups, Didzis
    Fiskeriverkets kustlaboratorium.
    Lundström, Karl
    Fiskeriverkets kustlaboratorium.
    Nissling, Anders
    Gotland University, School of Culture, Energy and Environment.
    Jonsson, Per
    Institutionen för marin ekologi, Göteborgs universitet.
    Uppföljning av fredningsområdet vid Gotska Sandön 2006-20102011Report (Other academic)
    Abstract [en]

    In March 2006 a 360 km2 large no-take area was established around the island Gotska Sandön in the central Baltic Sea, partly overlapping with the Salvorev-Kopparstenarna marine nature reserve. The purpose of the no-take area was to scientifically evaluate the effects of a fishing ban on fish stocks. A monitoring programme was setup to study the stocks in the reserve and in two reference areas, one east of Gotland where the fishing pressure is high and one in the partially protected Hoburgs bank, south of Gotland. Already before the closure Gotska Sandön had a lower fishing pressure than the two reference areas, which made it possible to evaluate the effects of lowfishing pressure in a short-term monitoring programme. The monitoring programme included fishing with survey nets, tagging of flatfishes and modelling of potential larval spread. An overview of the results is presented in the summary table (pages 10–11). Overall, the results showed a clear positive effect of the reserve on turbot (Scophthalmus maximus), with higher densities at Gotska Sandön compared to Gotland and also higher densities after the fishing ban compared to before the ban. This, in combination with the higher reproductive potential and the potential larval export from Gotska Sandön to Gotland, shows that the marine reserve may be important for maintaining aviable turbot stock at Gotland. The reserve did not have as clear effect on flounder (Platichthys flesus), although the densities were higher on Gotska Sandön compared to the reference areas and there is a potential for larval export from Gotska Sandön to Gotland. As expected, the reserve had no effect on the cod (Gadus morhua) stock. In contrast to flatfishes, the cod around Gotland does not form a local stock but isa peripheral part of the large cod population in the eastern Baltic Sea and hence is more affected by the stock status as a whole rather than by local fishery regulations at Gotska Sandön. In addition to being an important reproduction area for flatfishes, the marine reserve also acts as an important reference area for scientific studies since it is one of very few areas in the Baltic Sea where human activity is kept to a minimum. To protect these vital functions the are aaround Gotska Sandön should continue to be closed to fishing.

  • 2.
    Hinrichsen, Hans-Harald
    et al.
    GEOMAR Helmholtz Ctr Ocean Res Kiel, Dusternbrooker Weg 20, D-24105 Kiel, Germany..
    Petereit, Christoph
    GEOMAR Helmholtz Ctr Ocean Res Kiel, Dusternbrooker Weg 20, D-24105 Kiel, Germany..
    Nissling, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Isa
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Ustups, Didzis
    Inst Food Safety Anim Hlth & Environm BIOR, Daugavgrivas Str 8, LV-1048 Riga, Latvia..
    Florin, Ann-Britt
    Swedish Univ Agr Sci, Dept Aquat Resources, Inst Coastal Res, Skolgatan 6, S-74242 Oregrund, Sweden..
    Survival and dispersal variability of pelagic eggs and yolk-sac larvae of central and eastern baltic flounder (Platichthys flesus): application of biophysical models2017In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 74, no 1, p. 41-55Article in journal (Refereed)
    Abstract [en]

    A hydrodynamic model coupled with a Lagrangian particle tracking technique was utilized to simulate spatially and temporally resolved long-term environmentally related (i) size of habitat suitable for reproduction, (ii) egg/yolk-sac larval survival, (iii) separation of causes of mortality, and (iv) connectivity between spawning areas of Baltic flounder with pelagiceggs. Information on reproduction habitat requirements and mortality sources were obtained from field or laboratory studies. In our modelling study we only quantified physical processes generating heterogeneity in spatial distribution of eggs and yolk-sac larvae, as e.g. predation is not accounted for. The spatial extent of eggs and larvae represented as modelled particles is primarily determined by oxygen and salinity conditions. The reproduction habitat most suitable was determined for the Gdansk Deep, followed by the Bornholm Basin. Relatively low habitat suitability was obtained for the Arkona Basin and the Gotland Basin. The model runs also showed yolk-sac larval survival to be to a large extent affected by sedimentation. Eggs initially released in the Arkona Basin and Bornholm Basin are strongly affected by sedimentation compared with those released in the Gdansk Deep and Gotland Basin. Highest relative survival of eggs occurred in the Gdansk Deep and in the Bornholm Basin. Relatively low survival rates in the Gotland Basin were attributable to oxygen-dependent mortality. Oxygen content had almost no impact on survival in the Arkona Basin. For all spawning areas mortality caused by lethally low temperatures was only evident after severe winters. Buoyancy of eggs and yolk-sac larvae in relation to topographic features appear as a barrier for the transport of eggs and yolk-sac larvae and potentially limits the connectivity of early life stages between the different spawning areas.

  • 3.
    Hinrichsen, H-H
    et al.
    GEOMAR Helmholtz Ctr Ocean Res Kiel, Dusternbrooker Weg 20, D-24105 Kiel, Germany..
    Lehmann, A.
    GEOMAR Helmholtz Ctr Ocean Res Kiel, Dusternbrooker Weg 20, D-24105 Kiel, Germany..
    Petereit, C.
    GEOMAR Helmholtz Ctr Ocean Res Kiel, Dusternbrooker Weg 20, D-24105 Kiel, Germany..
    Nissling, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Ustups, D.
    Inst Food Safety Anim Hlth & Environm BIOR, Daugavgrivas Str 8, LV-1048 Riga, Latvia..
    Bergström, U.
    Swedish Univ Agr Sci, Dept Aquat Resources, Skolgatan 6, S-74242 Oregrund, Sweden..
    Hussy, K.
    Tech Univ Denmark, Natl Inst Aquat Resources, Jaegersborg Alle 1, DK-2920 Charlottenlund, Denmark..
    Spawning areas of eastern Baltic cod revisited: Using hydrodynamic modelling to reveal spawning habitat suitability, egg survival probability, and connectivity patterns2016In: Progress in Oceanography, ISSN 0079-6611, E-ISSN 1873-4472, Vol. 143, p. 13-25Article, review/survey (Refereed)
    Abstract [en]

    In the highly variable environment of the Baltic Sea two genetically distinct cod stocks exist, one west of the island of Bornholm, which is referred to as the western stock, and one to the east of Bornholm, the eastern stock. A hydrodynamic model combined with a Lagrangian particle tracking technique was utilised to provide spatially and temporally resolved long-term information on environmentally-related (i) spawning habitat size, (ii) egg/yolk-sac larval survival, (iii) separation of causes of mortality, and (iv) connectivity between spawning areas of eastern Baltic cod. Simulations were performed to quantify processes generating heterogeneity in spatial distribution of cod eggs and yolk sac larvae up to the first feeding stage. The spatial extent of cod eggs represented as virtual drifters is primarily determined by oxygen and salinity conditions at spawning, which define the habitat requirement to which cod's physiology is suited for egg development. The highest habitat suitability occurred in the Bornholm Basin, followed by the Gdansk Deep, while relatively low habitat suitability was obtained for the Arkona and the Gotland Basin. During drift egg and yolk sac larval survival is to a large extent affected by sedimentation. Eggs initially released in the western spawning grounds (Arkona and Bornholm Basin) were more affected by sedimentation than those released in the eastern spawning grounds (Gdansk Deep and Gotland Basin). Highest relative survival of eastern Baltic cod eggs occurred in the Bornholm Basin, with a pronounced decrease towards the Gdansk Deep and the Gotland Basin. Relatively low survival rates in the Gdansk Deep and in the Gotland Basin were attributable to oxygen-dependent mortality. Low oxygen content had almost no impact on survival in the Arkona Basin. For all spawning areas temperature dependent mortality was only evident after severe winters. Egg buoyancy in relation to topographic features like bottom sills and strong bottom slopes could appear as a barrier for the transport of Baltic cod eggs and yolk sac larvae and could potentially limit the connectivity of Baltic cod early life stages between the different basins in the western and eastern Baltic Sea. The possibility of an eastward directed transport up to the first-feeding larval stage exists only for eggs and yolk sac larvae at high buoyancy levels, suggesting that dispersal of early life stages between these spawning areas is limited.

  • 4. Limburg, Karin E.
    et al.
    Walther, Benjamin D.
    Lu, Zunli
    Jackman, George
    Mohan, John
    Walther, Yvonne
    Nissling, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Weber, Peter K.
    Schmitt, Axel K.
    In search of the dead zone: Use of otoliths for tracking fish exposure to hypoxia2015In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 141, p. 167-178Article in journal (Refereed)
    Abstract [en]

    Otolith chemistry is often useful for tracking provenance of fishes, as well as examining migration histories. Whereas elements such as strontium and barium correlate well with salinity and temperature, experiments that examine manganese uptake as a function of these parameters have found no such correlation. Instead, dissolved manganese is available as a redox product, and as such, is indicative of low-oxygen conditions. Here we present evidence for that mechanism in a range of habitats from marine to freshwater, across species, and also present ancillary proxies that support the mechanism as well. For example, iodine is redox-sensitive and varies inversely with Mn; and sulfur stable isotope ratios provide evidence of anoxic sulfate reduction in some circumstances. Further, S may be incorporated trophically whereas other elements appear to be taken up directly from water. This research suggests a potential means to identify individual fish exposure to hypoxia, over entire lifetimes. With further testing and understanding, in the future fish may be able to be used as "mobile monitors" of hypoxic conditions. (C) 2014 The Authors. Published by Elsevier B.V.

  • 5.
    Martinsson, Jesper
    et al.
    Gotland University, School of Culture, Energy and Environment.
    Nissling, Anders
    Gotland University, School of Culture, Energy and Environment.
    Nursery area utilisation by turbot (Psetta maxima) and flounder (Platichthys flesus) at Gotland, central Baltic Sea2011In: Boreal Environmental Research, ISSN 1239-6095, Vol. 16, no 1, p. 60-70Article in journal (Refereed)
    Abstract [en]

    To reveal the temporal and spatial utilization of a preferred nursery ground habitat by 0-group turbot and flounder in the Baltic Sea, sampling was conducted in six sandy bays in early-mid June to early-mid September 2003-2005 off the cost of Gotland (ICES SD 27 & 28-2). Settlement and peak abundance of turbot occurred from late July-early August to early September and from mid August to early September, respectively. Settlement of flounder occurred from early-mid-July with decreasing numbers over time, except in 2005. Peak abundance of 0-group flounder occurred in late July-ealy August to mid September, suggesting a considerable temporal overlap with 0-group turbot. 0-group turbot and flounder also overlapped in respect to depth with preferences for 0.2 and 0.6 m over 1 m. The spatial and temporal overlap of the species was verified by a logistic regression analysis; the probability of sampling 0-group flounder when 0-group turbot was caught in a haul was 0.84 (0.80-0.87, 95% CI).

  • 6.
    Nissling, Anders
    Gotland University, Department of Biology.
    Effects of temperature on egg and larval survival of cod (Gadus morhua) and sprat (Sprattus sprattus) in the Baltic Sea – implications for stock development2004In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 514, no 1-3, p. 115-123Article in journal (Refereed)
    Abstract [en]

    Stock development of cod and sprat, two major fish species in the Baltic Sea, is linked by trophic interactions. Depending on recruitment success the Baltic may be pushed towards either a cod- or a clupeid dominated system. Both cod and sprat spawn in the Baltic deep basins at strongly varying hydrographical conditions with survival during the egg and early larval stages regarded as a major bottleneck. Due to differences in egg specific gravity, cod and sprat eggs occur at different depths and are thus subject to different hydrographical conditions. For sprat, weak year-classes have been associated with low water temperatures during peak spawning. For cod the shift in peak spawning from spring to summer during the 1990s has been discussed as a reason for the poor recruitment at present as delayed spawning may involve egg development at too high temperatures. In the present study cod and sprat eggs and yolk sac larvae were incubated at different temperatures, 1–11thinsp°C for cod and 1–13thinsp°C for sprat. No difference in viable hatch occurred in the range 3–9thinsp°C for cod and in the range 5–13thinsp°C for sprat. Larval viability decreased at 11thinsp°C for cod and at le5thinsp°C for sprat. Comparing the results with vertical egg distribution and temperature profiles from field studies suggested no major influence of temperature on cod reproduction, but a considerable effect on sprat. The results imply that different environmental conditions; frequency of major saline water inflows into the Baltic Sea for cod, and water temperature in the upper layers, e.g. following severe/mild winters, for sprat, involve different opportunities for egg and larval survival and may thus cause a displacement in the balance between cod and sprat.

  • 7.
    Nissling, Anders
    et al.
    Gotland University, School of Culture, Energy and Environment.
    Dahlman, Gry
    Fecundity of flounder, Pleuronectes flesus, in the Baltic Sea: reproductive strategies in two sympatric populations2010In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 64, p. 190-198Article in journal (Refereed)
    Abstract [en]

    Two sympatric flounder populations with different reproductive strategies, offshore spawning at 10-20 psu producing pelagic eggs and coastal spawning at 5-7 psu with demersal eggs respectively, inhabit the brackish water Baltic Sea. Salinity governs the reproductive success by irregular saline water inflows and hence stock abundance and distribution. The potential fecundity (the standing stock of vitellogenic oocytes in the pre-spawning ovary) was assessed for fish sampled at five locations (two for offshore spawners and three for coastal spawners) along the salinity gradient (ICES SD 25, 27/28, 28 and 29).  Multiple linear regression analysis resulted in r2-values of 0.698-0.894 for the respective sampling location with somatic weight or total fish length as the main predictor, and otolith weight (proxy for age) and oocyte density (by gravimetric counting) as additional predictors. Analysis by univariate regressions using GLM revealed significantly higher fecundity for coastal spawning- than offshore spawning flounder (~69% more oocytes for an intermediate sized fish) but no intra-population differences. Similarly, gonad dry weight was significantly higher for coastal spawning flounder. Further, growth estimations indicated higher growth in offshore spawning- than in coastal spawning flounder suggesting that the coastal spawning population allocate relatively more resources into reproductive growth than somatic, potentially a result of strong selection for high fecundity of flounder producing demersal eggs due to poor egg survival for this spawning strategy. Earlier studies on fecundity of Baltic flounder are reviewed and discussed with consideration of inter-population differences questioning the idea of in general higher fecundity of flounder in the Baltic Sea.

  • 8.
    Nissling, Anders
    et al.
    Gotland University, School of Culture, Energy and Environment.
    Florin, Ann-Britt
    Institute of Coastal Research, Department of Aquatic Resources, Swedish University of Agricultural Sciences.
    Thorsen, Anders
    Institute of Marine Research, Bergen, Norway.
    Bergström, Ulf
    Institute of Coastal Research, Department of Aquatic Resources, Swedish University of Agricultural Sciences.
    Egg production of turbot, Scophthalmus maximus, in the Baltic Sea2013In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 84, p. 77-86Article in journal (Refereed)
    Abstract [en]

    In the brackish water Baltic Sea turbot spawn at ~6–9 psu along the coast and on offshore banks in ICES SD 2324–29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic 24oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old 25eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis 26identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of 27fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an ad- 28ditional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy 29for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity 30and gonad dry weight for turbot from SD 28 (3378–3474 oocytes/g somatic weight) compared to those 31from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05±0.03 mm diameter and 3246.8±6.5 μg dry weight; mean±sd). The difference in egg production matched egg survival probabilities 33in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer repro- 34ductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the 35limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring 36survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting 37spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is 38discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific 39year-classes, and effects of maturation status of sampled fish.

  • 9.
    Nissling, Anders
    et al.
    Gotland University, Department of Biology.
    Hinrichsen, Hans-Harald
    Institute of Marine Research, University of Kiel, Germany.
    Muller, Alajos
    Institute of Marine Research, University of Kiel, Germany.
    Andersson, Lars
    Swedish Meteorological and Hydrological Institute, Västra Frölunda, Sweden.
    Köster, Fritz
    Institute of Marine Research, University of Kiel, German.
    Makarchouk, Andrei
    Latvian Fisheries Research Institute, Riga, Latvia.
    Vertical distribution and egg survival of Baltic sprat in relation to temperature and oxygen conditions - implications for stock development2002Conference paper (Other academic)
    Abstract [en]

    Sprat, Sprattus sprattus, is a key species in the Baltic Sea. Besides being a target species in the Baltic mixed clupeoid fishery it is a major zooplanktivore and dominates, together with herring, one of four trophic levels in the Baltic Sea food web. Occasionally strong year classes of Baltic sprat are followed by a number of year classes below average. During the 1990s however a series of year classes above average were produced and the stock reached historically high levels with implications for the Baltic food web. Spawning stock biomass and recruitment are poorly related suggesting that environmental conditions have a great impact on the year-class strength. In the main spawning areas, i.e. the Baltic deep basins, egg development occurs at highly varying environmental conditions. In the present investigation egg specific gravity and variation in vertical egg distribution as well as egg survival in relation to temperature and oxygen conditions were studied. Incubation of eggs revealed significantly lower viable hatch at <5 degree C. Egg occurrence in relation to oxygen concentration suggested lower survival at <2 ml/l. Egg specific gravity averaged 1.00858 plus or minus 0.00116 g/cm3 during peak spawning but was significantly higher early in the season and significantly lower towards the end of the spawning period. In general, eggs kept buoyant in the deep layers at low oxygen conditions early in the season, developed at more favourable oxygen concentrations but at poor temperature conditions during peak spawning, and were distributed at both more favourable temperature and oxygen conditions towards the end of the spawning season. Using conditions at in average occurrence of eggs during peak spawning for the period 1970-2000 the relative importance of temperature and oxygen conditions was evaluated. Results suggested that variation in temperature is the most important factor affecting egg survival in the Bornholm basin (SD 25), that mainly oxygen conditions determine the survival rate in the Gotland basin (SD 28) whereas variation in both temperature and oxygen conditions influence survival in the Gdansk Deep (SD 26). In conclusion, opportunities for egg survival are influenced by both temperature conditions following mild or severe winters as well as by frequency and magnitude of saline water inflows into the Baltic Sea.

  • 10.
    Nissling, Anders
    et al.
    Gotland University, Department of Biology.
    Jacobsson, Marie
    Hallberg, Nina
    Feeding ecology of juvenile turbot Scophthalmus maximus and flounder Pleuronectes flesus at Gotland, Central Baltic Sea2007In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 70, no 6, p. 1877-1897Article in journal (Refereed)
    Abstract [en]

    Food and feeding of juvenile turbot Scophthalmus maximus and flounder Pleuronectes flesus were studied in five nursery areas at Gotland, Central Baltic Sea, ICES SD 27 and SD 28. Ontogeny involved partitioning of available food resources. The food choice of turbot <30 mm standard length (L sub(S)) included both planktonic-hyperbenthic prey (calanoid copepods and mysids) and epibenthic-endobenthic prey (chironomids and amphipods), whereas turbot greater than or equal to 30 mm L sub(S) fed mainly on hyperbenthic species (mysids and fishes). Conversely, for flounder, epibenthic-endobenthic prey were the most abundant prey items throughout development (harpactocoid copepods, oligochaetes and chironomids for fish <40 mm L sub(S) and oligochaetes, chironomids and amphipods for flounder greater than or equal to 40 mm L sub(S)). Thus, the highest degree of dietary overlap occurred between turbot <30 mm and flounder greater than or equal to 40 mm. Food composition for both turbot and flounder varied, however, according to exposure and predominant wind direction in the nursery area. For example, expressed as the ratio between the biomass of mysids and fishes consumed, the relative importance of mysids v. fishes as food source for turbot, varied from <1 in the most sheltered area to 16 and 27 in the more open areas. Considerable differences in feeding incidence were recorded; mean plus or minus s.d. 58 plus or minus 20% for turbot <30 mm L sub(S) and 83 plus or minus 8% for turbot greater than or equal to 30 mm L sub(S), as opposed to greater than or equal to 85-90% for flounder irrespective of size. The lower feeding success of turbot <30 mm L sub(S) was related to mysid abundance, shown to vary spatially and temporally, and to density of flounder, indicating that food availability, and potentially interspecific competition, influence feeding of early juvenile turbot with implications for survival following settlement. Regarding variability in abundance, hyperbenthic prey, as mysids, are considered more variable than epi- and endobenthic organisms. Hence, in addition to the 'nursery size hypothesis', i.e. the positive relationship between abundance of recruits and extension of nursery areas, variability in food availability may explain the average lower recruitment of turbot as compared to other flatfishes, e.g. flounder.

  • 11.
    Nissling, Anders
    et al.
    Gotland University, Department of Biology.
    Johansson, Ulrika
    Jacobsson, Marie
    Effects of salinity and temperature conditions on the reproductive success of turbot (Scophthalmus maximus) in the Baltic Sea2006In: Fisheries Research, ISSN 0165-7836, E-ISSN 1872-6763, Vol. 80, no 2-3, p. 230-238Article in journal (Refereed)
    Abstract [en]

    In the Baltic Sea, a large brackish water area, turbot (Scophthalmus maximus) occurs at the border of its distribution with respect to salinity. Using turbot caught in ICES subdivision (SD) 28 (mid-Baltic), salinity requirements for successful egg development were evaluated by assessment of spermatozoa mobility, fertilisation and egg survival at different salinities. Further, to evaluate potential effects of temperatures, egg survival at different temperatures was assessed. Spermatozoa activity and fertilisation rate decreased with decreasing salinity with a significant drop at <7 psu. The viable hatch was significantly lower at <7 psu compared to at 7–15 psu. Hence, due to decreasing salinity this implies lower egg survival in SD 29 and 30 compared to in SD 24–28, and that salinity conditions in SD 31 are insufficient for egg development. Further, following a long period without major inflows of saline water into the Baltic Sea, salinity has decreased. From 1995 onwards salinities <7 psu prevail in SD 27–28 suggesting decreased reproductive success and potentially weaker year-classes in this area. Egg survival was high at 12–18 °C and considerably lower at 9 and 21 °C. Comparing the results with environmental data suggested that spawning time of turbot is adapted to optimum temperatures for egg development, but that occasions with temperatures involving increased egg mortality may occur, e.g. during upwelling situations.

  • 12.
    Nissling, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Larsson, R
    Population specific sperm production in flounder Platichtys flesus - adaptation to salinity at spawning2018In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649Article in journal (Refereed)
  • 13.
    Nissling, Anders
    et al.
    Gotland University, Department of Biology.
    Muller, Alajos
    Institute of Marine Research, University of Kiel, Germany.
    Hinrichsen, Hans-Harald
    Institute of Marine Research, University of Kiel, Germany.
    Specific gravity and vertical distribution of sprat eggs in the Baltic Sea2003In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 63, no 2, p. 280-299Article in journal (Refereed)
    Abstract [en]

    During peak spawning of sprat Sprattus sprattus in the Baltic Sea in May-June egg specific gravity averaged plus or minus s.d. 1 times 00858 plus or minus 0 times 00116 g cm super(-3) but was significantly higher in the beginning and significantly lower towards the end of the spawning season. A close relationship was found between egg diameter and egg specific gravity (r super(2) = 0 times 71). This relationship, however, changed during the spawning season indicating that some other factor was involved causing the decrease in specific gravity during the spawning period. The vertical egg distribution changed during the spawning season: eggs were distributed mainly in the deep layers early in the season, occurred in and above the permanent halocline during peak spawning, and above the halocline towards the end of the spawning season. Consequently, poor oxygen conditions in the deep layers and low temperatures in layers between the halocline and the developing thermocline may affect egg development. Thus, opportunities for egg development vary over the spawning season and among spawning areas, and depending on frequency of saline water inflows into the Baltic Sea and severity of winters, between years.

  • 14.
    Nissling, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Nyberg, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Petereit, Christoph
    GEOMAR Helmholtz Ctr Ocean Res Kiel, D-24105 Kiel, Germany..
    Egg buoyancy of flounder, Platichthys flesus, in the Baltic Sea-adaptation to salinity and implications for egg survival2017In: Fisheries Research, ISSN 0165-7836, E-ISSN 1872-6763, Vol. 191, p. 179-189Article in journal (Refereed)
    Abstract [en]

    Vertical distribution of eggs as determined by the egg buoyancy, i.e. the difference in specific gravity between the egg and the ambient water, have profound implications for the reproductive success and hence recruitment in fish. Here variability in egg specific gravity of flounder, Platichthys flesus, was studied along a salinity gradient and by comparing two reproductive strategies, spawning pelagic or demersal eggs. Egg characteristics of 209 egg batches (covering ICES subdivisions (SD) 22-29 in the brackish water Baltic Sea) was used to reveal the significance of egg diameter and egg dry weight for egg specific gravity (ESG), subpopulations, and egg survival probabilities of pelagic eggs following a major saline water inflow event. As an adaptation to salinity, ESG (at 7 degrees C) differed (p <0.001) between areas; three subpopulations of flounder with pelagic eggs: 1.0152 +/- 0.0021 (mean +/- sd)g cm(-3) in SD 22, 1.0116 +/- 0.0013 g cm(-3) in SD 24 and 25, and 1.0096 +/- 0.0007 g cm(-3) in SD 26 and 28, contrasting to flounder with demersal eggs, 1.0161 +/- 0.0008 g cm(-3). Egg diameter differed (p <0.001) between subpopulations; from 1.08 +/- 0.06 mm (SD 22) to 1.26 +/- 0.06 mm (SD 26 and 28) for pelagic eggs and 1.02 +/- 0.04 mm for demersal eggs, whereas egg dry weight was similar; 37.9 +/- 5.0 mu g (SD 22) and 37.2 +/- 3.9 mu g (SD 28) for pelagic, and 36.5 +/- 6.5 mu g for demersal eggs. Both egg diameter and egg dry weight were identified as explanatory variables, explaining 87% of the variation in ESG. ESG changed during ontogeny; a slight decrease initially but an increase prior to hatching. Egg survival probabilities judged by combining ESG and hydrographic data suggested higher egg survival in SD 25 (26 vs 100%) and SD 26 (32 vs 99%) but not in SD 28 (0 and 3%) after the inflow event, i.e. highly fluctuating habitat suitability. The results confirm the significance of ESG for egg survival and show that variability in ESG as and adaptation to salinity is determined mainly by water content manifested as differences in egg diameter; increase in diameter with decreasing salinity for pelagic eggs, and decreased diameter resulting in demersal eggs.

  • 15.
    Nissling, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Thorsen, A.
    Inst Marine Res, POB 1870, N-5817 Bergen, Norway..
    da Silva, F. F. G.
    Inst Marine Res, POB 1870, N-5817 Bergen, Norway.;Tech Univ Denmark, Natl Inst Aquat Resources, Alle 1, DK-2920 Charlottenlund, Denmark..
    Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea2016In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 88, no 4, p. 1301-1320Article in journal (Refereed)
    Abstract [en]

    Down-regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean +/- s.d. total length of the sampled fish was 327 +/- 31cm and mean +/- s.d. age was 62 +/- 15years. Measurements of atresia were performed using the profile method' with the intensity of atresia adjusted according to the dissector method' (106% adjustment; coefficient of determination was 0675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down-regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.

  • 16.
    Nissling, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Thorsen, Anders
    da Silva, Filipa F.G
    Fecundity regulation in relation to habitat utilisation of two sympatric flounder (Platichtys flesus) populations in the brackish water Baltic Sea2015In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 95, p. 188-195Article in journal (Refereed)
    Abstract [en]

    Two populations of flounder (Platichtys flesus) with different life history traits inhabit the brackish water Baltic Sea. Both types share feeding areas in coastal waters during summer-autumn but utilise different habitats for spawning in spring, namely offshore spawning with pelagic eggs and coastal spawning with demersal eggs respectively. Fecundity regulation by atresia was assessed as prevalence (portion of fish with atresia) and intensity (calculated as the average intensity of atresia in these fish) during the reproductive cycle following start of gonad development in the autumn up to spawning in spring, and evaluated in relation to fish condition (Fulton's condition factor reflecting energy reserves of the fish) and feeding incidence of the respective population. Peaking in winter (December–February), fecundity regulation was significantly higher for coastal spawning flounder than for flounder spawning offshore. For coastal spawners, the prevalence was 45–90% with an intensity of 6.4–9.3% vs. 0–25% and an intensity of 2.1–3.4% for offshore spawners during winter. Further, fecundity regulation ceased prior to spawning for offshore spawners but continued for coastal spawners. For coastal spawners, the prevalence was 12–29% and an intensity of 2.5–6.1% during spawning. The change in fish condition was strongly related to feeding incidence and differed between populations. As feeding ceased, condition of offshore spawners decreased during winter up to spawning, whereas condition of coastal spawners decreased during autumn but was maintained as feeding started again prior to spawning. Thus, habitat utilisation according to spawning strategy affects the timing of fecundity down-regulation reflecting availability of resources, namely limited food resources in deep areas and higher availability in coastal areas. Offshore spawning flounder display characteristics typical for a capital spawner with ceasing of feeding and oocyte down-regulation well before spawning, whereas coastal spawning flounder can be characterised as intermediate between a capital and income spawner with feeding prior to and during spawning along with continuous fecundity-regulation.

  • 17.
    Nissling, Anders
    et al.
    Gotland University, Department of Biology.
    Westin, Lars
    Hjerne, Olle
    Department of Systems Ecology, Stockholm University.
    Reproductive success in relation to salinity for three flatfish species, dab (Limanda limanda), plaice (Pleuronectes platessa), and flounder (Pleuronectes flesus), in the brackish water Baltic Sea2002In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 59, no 1, p. 93-108Article in journal (Refereed)
    Abstract [en]

    The reproductive success and thus abundance and distribution of dab, plaice, and flounder in the Baltic Sea, a large brackish water area, is restricted by salinity. By measuring spermatozoa mobility and fertilisation rates at different salinities and determining the salinity at which eggs are neutrally buoyant, the salinity requirements for successful egg development were assessed. The results were used for the evaluation of potential spawning areas and for stock discrimination by analyses of differences in the salinity requirements of fish from different areas (ICES Subdivisions (SD) 23–28). The results suggest that there are two stocks of dab and successful reproduction may occur in the Sound (SD 23) and, occasionally, in the Arkona and Bornholm basins (SD 24 and SD 25). Opportunities for successful reproduction of plaice exist regularly in the Arkona and Bornholm basins and occasionally in the Gdansk and Gotland basins (SD 26 and SD 28). No differences in salinity requirements for fish from SD 24–28 suggest one stock of plaice in the Baltic proper. There are two different types of flounder, one with demersal eggs and the other with pelagic eggs. The former, constituting one distinct stock, may reproduce successfully as far north as the Bothnian Sea and the Gulf of Finland (SD 30 and SD 32), up to the 6 psu isohaline. For flounder with pelagic eggs, opportunities for the eggs to obtain neutral buoyancy suggest that successful reproduction may occur regularly in the Sound, the Arkona, and Bornholm basins as well as in the Gdansk and Gotland basins, and that there are three stocks of flounder with pelagic eggs.

  • 18.
    Vallin, Lars
    et al.
    Gotland University, Department of Biology.
    Nissling, Anders
    Gotland University, Department of Biology.
    Maternal effects on egg size and egg buoyancy of Baltic cod, Gadus morhua: Implications for stock structure effects on recruitment2000In: Fisheries Research, ISSN 0165-7836, E-ISSN 1872-6763, Vol. 49, no 1, p. 21-37Article in journal (Refereed)
    Abstract [en]

    Successful spawning of cod in the Baltic is restricted to the deep basins: the Bornholm basin, the Gdansk Deep and the Gotland basin, at salinities varying between 11 and 20 psu. Due to oxygen-depletion commonly prevailing in these areas, neutral egg buoyancy above oxygen-critical levels is of substantial importance for egg and larval survival in the Baltic. In the present study, large females were found to produce larger eggs with neutral egg buoyancy at a lower salinity, implying egg development in more favourable oxygen conditions. An age- and batch-specific model of egg production, egg size and egg buoyancy showed a substantial increase in the probability of egg survival with female age. The relationship between egg production by old females and subsequent recruitment was tested in two separated periods with different conditions: 1967-1980 and 1981-1994. The number of recruited cod (age 2), in the Baltic Sea, was positively related to the fraction of eggs produced by old females ( greater than or equal to 5 years). That recruitment was positively related to the proportion of eggs spawned by old fish reveals that stock age structure should be seriously considered in stock-recruitment relationships and in the management of the cod stock in the Baltic.

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