Linking the diversity of fish assemblages to habitat structure: A study on Dogger Bank (North Sea) (original) (raw)
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Journal of Sea Research, 2013
The interdependence between groundfish assemblages and habitat properties was investigated on the Dogger Bank in the North Sea. Abiotic habitat parameters considered included topography, hydrographic conditions, sediment composition, and the biotic habitat variable the prevailing benthic invertebrates. Distinct epi-and infauna communities occurred at different locations on the Dogger Bank. Fish assemblages were clearly linked to both the biotic and abiotic habitat characteristics.
Linking spatial pattern of bottom fish assemblages with water masses in the North Sea
Fisheries Oceanography, 2009
Understanding the links between large scale spatial structuring of fish assemblages and shaping factors is essential to develop comprehensive ecosystem-based fisheries management. In this study, we investigated spatial patterns of bottom fish assemblages in the North Sea in relation to prevailing water masses in the region. We based our analysis on catch data from the German Small-Scale Bottom Trawl Survey conducted between 1987 and 2005 and used both ordination techniques and Mantel tests. Spatial variability of bottom fish assemblages was larger than inter-annual variability. Five significantly different bottom fish assemblages were associated with the following prevailing hydrographical regimes: i) the English Channel, ii) Continental Coastal, iii) central North Sea, iv) northern North Sea, and v) northern Atlantic water masses. Associations were generated by gradients in relative proportions of abundant species such as grey gurnard (Eutrigla gurnardus), dab (Limanda limanda), whiting (Merlangius merlangus), haddock (Melanogrammus aeglefinus) and Norway pout (Trisopterus esmarki). Taking into account large scale spatial structuring of catch data Mantel tests confirmed significant correlation between the fish assemblages and hydrographical variables. In summary, our results strongly support the hypotheses that hydrographical features such as water masses, fronts, and residual currents could shape bottom fish associations in the North Sea. Spatial demarcations of bottom fish assemblages indicated by this study can be used to support ecosystem-based fisheries management strategies.
Persistence and variation in the distribution of bottom-trawl fish assemblages over the Flemish Cap
Journal of Northwest Atlantic Fishery Science, 2006
The aim of this study is to test the variability of the assemblages defined in the Flemish Cap area. Data from 951 bottom hauls were analysed, covering depths between 126 and 740 m in the years 1995-2002. The fish fauna in Flemish Cap appears distributed in a persistent structural zonation defined in three assemblages. The first three factors of a Principal Component Analysis explained the 78.4% of the variance in distribution species, and they are consistent with the results of a cluster analysis. The three characteristic assemblages show a temporal persistence, but some changes appear in this period, for instance: displacements of the assemblages limits towards shallower waters, and some changes in relative position of the dominant species in each assemblage. These changes can be related with the constant decrease of the biomass of the main demersal fish species like Atlantic cod and American plaice. The species of Genus Sebastes appear as dominant fish species in the area.
2007
region when catchability in the GOV was accounted for. However, when based on the raw bundance data, diversity appeared highest in the southeastern North Sea, again stressing the d on the von Bertalanffy growth function nd weight at length relationships, is presented. A linear regression method for estimating the a importance of considering catchability in the sampling gear. Similar spatial community composition clustering was observed for the fished component of the demersal fish assemblage, as when the entire community was considered. A method for estimating growth productivity of the fish assemblage from the species abundance at length data provided by the groundfish surveys, base a required parameter values for each species sampled in the surveys is described. As with diversity, accounting for species-and size-related catchability in the GOV trawl profoundly affected the resulting maps of spatial variation in biomass density, production density and production:biomass (P/B) ratios. Spatial patterns of productivity and P/B ratio differed between different weight-class components of the demersal fish assemblage. Productivity in the prey-fish component of the assemblage (Log 2 weight-classes 3 and 4) was highest in the northern North Sea.
Marine Ecology Progress Series, 2008
Conserving and restoring biodiversity are key objectives for an ecosystem approach to management in the North Sea, but ecological quality objectives for the groundfish community instead concentrate on restoring size structure. Species richness and diversity estimates are strongly influenced by sampling effort. Failure to account for this has led to the belief that species richness and diversity indices are not adequate indicators of 'state' for the groundfish community. However, adherence to a standard procedure that is robust within respect to sampling effort influence should allow these metrics to perform a state indicator role. The Arrhenius power and Gleason semi-log species-area relationships are examined to determine whether they can provide modelled estimates of species richness at the ICES (International Council for the Exploration of the Sea) rectangle scale. Of these, the Gleason semi-log appears most reliable, particularly when a randomised aggregation process is followed. Aggregation of at least 20 trawl samples is required to provide empirically derived index values that are representative of the communities sampled, and therefore sensitive to drivers of change in these communities. However, given current groundfish survey sampling levels, combining 20 half-hour trawl samples to provide single estimates of species richness and diversity will require considerable aggregation over time and/or space. This can lead to estimates of α or local richness/ diversity becoming inflated through the inclusion of elements of β or regional richness/diversity. For the North Sea groundfish assemblage, this occurs when the distance between the focal position and the location of the most distant sample exceeds 49 km.
Marine Biology Research, 2005
Geostatistics was employed to investigate spatial structuring of herring, cod, dab, haddock and whiting at different spatial scales in the northern North Sea. Additionally, a structural analysis of the maximum water depth was carried out to assess habitat associations of fish. Linear, spherical, exponential and Gaussian models were fitted to the semivariograms, showing clear spatial autocorrelations. At the smaller scale, spatial structuring was weak for haddock, herring and dab, increasing at the larger spatial scale, with the exception of whiting. Mean catch rates, estimated classically and geostatistically, were in good agreement. Corresponding variances were clearly reduced at both spatial scales, when accounting for spatial distribution of the fish. At the larger survey scale a high level of habitat association was detected for haddock and whiting, while a poor habitat association was found for cod, dab and herring. The smaller scale seems to be the threshold at which spatial structuring of cpue could have marked influence on estimation error. Thus, survey scale is important when analysing spatial patterns and estimating mean biomass indices, and a sound analysis of relations in spatial structuring of fish and habitat conditions is essential to derive more precise estimates.