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  • 1
    Publication Date: 2019-04-15
    Description: Genetic data have great potential for improving fisheries management by identifying the fundamental management units—that is, the biological populations—and their mixing. However, so far, the number of practical cases of marine fisheries management using genetics has been limited. Here, we used Atlantic cod in the Baltic Sea to demonstrate the applicability of genetics to a complex management scenario involving mixing of two genetically divergent populations. Specifically, we addressed several assumptions used in the current assessment of the two populations. Through analysis of 483 single nucleotide polymorphisms (SNPs) distributed across the Atlantic cod genome, we confirmed that a model of mechanical mixing, rather than hybridization and introgression, best explained the pattern of genetic differentiation. Thus, the fishery is best monitored as a mixed-stock fishery. Next, we developed a targeted panel of 39 SNPs with high statistical power for identifying population of origin and analyzed more than 2,000 tissue samples collected between 2011 and 2015 as well as 260 otoliths collected in 2003/2004. These data provided high spatial resolution and allowed us to investigate geographical trends in mixing, to compare patterns for different life stages and to investigate temporal trends in mixing. We found similar geographical trends for the two time points represented by tissue and otolith samples and that a recently implemented geographical management separation of the two populations provided a relatively close match to their distributions. In contrast to the current assumption, we found that patterns of mixing differed between juveniles and adults, a signal likely linked to the different reproductive dynamics of the two populations. Collectively, our data confirm that genetics is an operational tool for complex fisheries management applications. We recommend focussing on developing population assessment models and fisheries management frameworks to capitalize fully on the additional information offered by genetically assisted fisheries monitoring.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
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    Regional Euro-Asian Biological Invasions Centre - REABIC
    In:  Aquatic Invasions, 3 (2). pp. 113-124.
    Publication Date: 2016-09-06
    Description: The distribution and abundance of the invasive ctenophore Mnemiopsis leidyi in the Bornholm Basin, an important spawning ground of several fish stocks, and in adjacent areas in the central Baltic Sea was studied in November 2007. The study showed that M. leidyi were relatively small (body length 18.6 ± 7.6 mm) and they were patchily distributed over a large part of the investigated area. Specimens were found on 68 and 59% of stations sampled with a Bongo net (n=39) and an Isaac-Kidd midwater trawl (n=51), respectively. Vertically, the highest densities of M. leidyi occurred at 40 to 60 m around the halocline. Horizontally, the highest abundances were found north and west of Bornholm, but relatively high densities were also observed in the Slupsk Furrow. The mean abundance was 1.58 ± 2.12 ind. m-2, the peak abundance was 8.92 ind. m-2, and the average and peak population density were 0.03 ± 0.05 and 0.28 ind. m-3, respectively. The abundances are low compared to densities recently observed in other areas of the Baltic region (e. g. Limfjorden, Åland Sea) and the estimated predation impact on zooplankton by M. leidyi was negligible in November 2007. However, because of the ctenophore’s wide distribution in the central Baltic Sea, its ability for rapid population growth, and its potential influence on fish stocks by competing for food and by preying on fish eggs and newly hatched larvae, close monitoring of the future development of M. leidyi in the Baltic Sea is strongly recommended.
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  • 5
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    In:  [Poster] In: NAFO ICES PICES Symposium on Reproductive and Recruitment Processes of Exploited Marine Fish Stocks, 01.-03.10, Lissabon, Portugal .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    In:  [Poster] In: FRESH (COST action FA0601) Workshop, 15.-19.06, Cadiz, Spain .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
    Publication Date: 2012-02-23
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  • 8
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    In:  (Doctoral thesis/PhD), Christian-Albrechts-Universität, Kiel, Germany, 133 pp
    Publication Date: 2012-07-06
    Description: Sprat is an important ecological key species in the Baltic Sea. Temporal and spatial variability in reproductive traits of Baltic sprat was investigated in relation to biotic and abiotic parameters. The seasonality of important spawning traits were analysed. Models of sex ratio and maturity at length were established. The ovarian dynamics in relation to postovulatory follicles (POF) were described with the major finding that the degeneration of POF equals the spawning interval. A temperature dependent model on Baltic sprat egg development was established. All obtained results were finally used to implement the Daily Egg Production Method (DEPM) to the Baltic sprat stock. The knowledge obtained by the present thesis will serve as basis to (i) enhance existing assessment methods and to test alternative indices for sprat stock reproductive potential, (ii) implement alternative assessment methods and (iii) further investigate the population dynamics and ecology of Baltic sprat.
    Type: Thesis , NonPeerReviewed
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  • 9
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    Elsevier
    In:  Journal of Sea Research, 67 (1). pp. 27-33.
    Publication Date: 2017-07-19
    Description: Ovaries of Baltic sprat (Sprattus sprattus balticus S.) were analysed histologically to identify stages of postovulatory follicles (POF) and to assess the oocyte development pattern. Samples were taken every 3 h during a 24 h trawl survey conducted in the Bornholm Basin in April 2007. Gonad histology revealed spawning of sprat throughout the day which hampered the exact ageing of POFs by the postovulatory follicle method and therefore did not allow direct estimation of spawning frequency. However, it was possible to define four stages of POFs, according to their histological features. The occurrence of these POF stages (I to IV) corresponded clearly to the development of the leading oocyte cohort. Further, the oocyte recruitment pattern revealed that the spawning batch can be identified prior to hydration. The POF stages I and II were present almost exclusively in vitellogenic ovaries, POF III were found in ovaries in the germinal vesicle stage, and the most deteriorated POF stage IV was found in actively spawning fish with hydrated oocytes. Since POF were absent only in very few ovaries (5%), and in each ovary in general only one POF stage was present, the duration of POF degeneration approximately equals the average batch interval, i.e. the time lag between subsequent spawning events. The results of the present study will serve as basis for future studies on Baltic sprat oocyte recruitment and daily spawning fraction. Highlights: ► Histological classification of sprat gonad development stages. ► Histological classification of POF in sprat in relation to gonad developmental stages. ► Daily spawning pattern of Baltic sprat.
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  • 10
    Publication Date: 2018-12-11
    Description: Baltic sprat (Sprattus sprattus balticus, Schneider 1908) is a key species in the Baltic Sea ecosystem, where it is the most abundant planktivorous fish. In the present study, we applied the daily egg production method (DEPM) for the years 1999–2008 to estimate the size of the stock component reproducing in the Bornholm Basin, a major spawning ground for sprat and cod. This is the first study assessing this stock with a fishery independent egg production method for a consecutive time series of ten years. DEPM stock size estimates were compared with those obtained by a multi species virtual population analysis for the same stock component and results from an acoustic survey. In general, the results obtained by the DEPM were in the same order of magnitude compared to the other methods and most similar to the acoustic estimate. However, in some years differences between methods were substantial. With respect to previous egg production methods to assess Baltic sprat stock components our approach takes several aspects into account which were ignored before, e.g. effect of ambient temperature range on sprat egg stage duration and mortality and interannual variability of adult stock parameters. Since the accurate determination of the daily spawning fraction bears major uncertainties, different scenarios were tested for this parameter. Least deviation compared to the other assessment methods was obtained when using a daily female spawning fraction of 24%, which corresponds well to values described in literature. The applicability of the DEPM to Baltic sprat was clearly demonstrated. Thus, it can serve as valuable tool for the estimation of Baltic sprat stock sizes independent of data obtained from commercial fisheries.
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