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  • 1
    facet.materialart.
    Unbekannt
    Urban & Fischer
    In:  Archive of Fishery and Marine Research, 49 . pp. 103-116.
    Publikationsdatum: 2017-12-12
    Beschreibung: The ICES International Herring Larvae Survey Program (IHLS), regularly carried out since 1972 in the North Sea and adjacent areas, provides an abundance index to be utilised by the ICES Herring Assessment Working Group. This is one of three indices for assessing the state of the herring stock components in the North Sea by means of VPA (Virtual Population Analysis) related numerical procedures. Due to a substantial decline in ship time and sampling effort since the end of the 1980s, it was necessary to revise the IHLS survey design and the related procedure for calculating larval abundance indices, as major constraints of the formerly used indices (LAI, LPE) had been strongly violated. Using the historical herring larvae data base, which was transferred from Aberdeen (Scotland) to Kiel (Germany) in 1997, the current article analyses statistically the effects of this decline in effort, derives the optimum effort and presents its optimal allocation to specific sampling units defined by space and time. All investigations have been performed on the basis of an abundance index (MLAIyear) introduced in 1994 (Patterson and Beveridge 1994), which was derived from a linearized multiplicative model approach (log-transformed multifactor ANOVA). This MLAI approach was modified by introducing a weighting factor per sampling unit, taking into account differences in the spatial coverage of sampling and in the variation among stations within these sampling units
    Materialart: Article , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Publikationsdatum: 2017-08-23
    Beschreibung: We used otolith microstructure analysis to reconstruct the growth histories of larval radiated shanny ( Ulvaria subbifurcata ) collected over a 2-week period in Trinity Bay, Newfoundland. A dynamic 3-dimensional, eddy-resolving circulation model of the region provided larval drift patterns, which were combined with measurements of temperature and zooplankton abundance to assess the environmental history of the larvae. The abundance of juvenile and adult capelin ( Mallotus villosus ), the dominant planktivorous fish in this area, was monitored using five hydroacoustic surveys. The goal was to determine whether environmental histories are helpful in explaining spatial and temporal differences in larval shanny growth, measured as cumulative distribution functions (CDF) of growth rates. We found evidence for a selective loss of slower growing individuals and recognized considerable spatial differences in the CDF of larval growth rates. Consistent patterns in capelin abundance suggested that faster growing survivors, sampled at the end of the 2-week period, developed in areas of low predator densities. A dome-shaped relationship between temperature and larval growth was observed, explaining a significant but small amount of the overall variability (14%). Effects of experienced prey concentrations on larval growth rates could not be demonstrated.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    facet.materialart.
    Unbekannt
    Oxford Univ. Press
    In:  ICES Journal of Marine Science, 64 . pp. 956-962.
    Publikationsdatum: 2019-09-23
    Beschreibung: Ontogenetic and diurnal vertical migration patterns of Baltic sprat larvae were investigated for the periods 1989–1990 and 1998–2002. Comparison of the results led to the hypothesis that the diel vertical migration behaviour of sprat larvae 〉10 mm has changed. In 1989 and 1990, sprat larvae migrated to the surface at night, whereas they stayed 30–50 m deep by day. From 1998 to 2002, sprat larvae showed no signs of diel vertical migration, remaining in warmer, near-surface water by day and night. This behavioural change coincided with a more general change in the Baltic ecosystem, i.e. an increase in near-surface temperature and a general increase in abundance of the major prey organism (Acartia spp.) of Baltic sprat larvae, with more pronounced aggregation in surface waters.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Publikationsdatum: 2017-05-17
    Beschreibung: Large-scale climatic conditions prevailing over the central Baltic Sea resulted in declining salinity and oxygen concentrations in spawning areas of the eastern Baltic cod stock. These changes in hydrography reduced the reproductive success and, combined with high fishing pressure, caused a decline of the stock to the lowest level on record in the early 1990s. The present study aims at disentangling the interactions between reproductive effort and hydrographic forcing leading to variable recruitment. Based on identified key processes, stock dynamics is explained using updated environmental and life stage-specific abundance and production time-series. Declining salinities and oxygen concentrations caused high egg mortalities and indirectly increased egg predation by clupeid fish. Low recruitment, despite enhanced hydrographic conditions for egg survival in the mid-1990s, was due to food limitation for larvae, caused by the decline in the abundance of the copepod Pseudocalanus sp. The case of the eastern Baltic cod stock exemplifies the multitude effects climatic variability may have on a fish stock and underscores the importance of knowledge of these processes for understanding stock dynamics.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    facet.materialart.
    Unbekannt
    Oxford Univ. Press
    In:  Journal of Plankton Research, 30 . pp. 529-550.
    Publikationsdatum: 2018-06-05
    Beschreibung: The abundance and vertical distribution of microcopepods sampled by nets with 55 μm mesh size was compared for two neighbouring but hydrographically different areas, the Gulf of Aqaba and the northernmost Red Sea, during spring 1999. The vertical structure of the total microcopepod communities differed considerably between the two regimes: In the stratified waters of the Red Sea, calanoids outnumbered oncaeids as well as oithonids at 0–100 m, whereas oncaeids dominated in all meso- and bathypelagic layers below 100 m deep. In the unusually deep vertically mixed waters of the Gulf of Aqaba, calanoids outnumbered each of the non-calanoid taxa as deep as 250 or 350 m, whereas the oncaeid dominated deep water community was restricted to depth ranges below 400 m. Dominant non-calanoid species in both areas were Oncaea bispinosa, Paroithona pacifica, Oithona simplex, Spinoncaea ivlevi, O. tregoubovi and O. cristata. O. scottodicarloi occurred in exceptionally high numbers in the northern Gulf. Pronounced differences between the two areas were found in the vertical distribution of poecilostomatoid species. By comparing the present results with published data from the central and southern Red Sea and other tropical and warm-temperate oceanic areas, intra- and inter-oceanic differences in the structure of microcopepod communities in oligotrophic areas are discussed. The high abundance and vertically extended range of calanoid copepods during spring appears to be a specific feature of the Gulf of Aqaba, indicating an unusual vertical succession in the trophodynamic structure of the copepod fauna in this area.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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