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Different surveys provide similar pictures of trends in a marine fish community but not of individual fish populations ArchiMer
Trenkel, Verena; Pinnegar, John; Rochet, Marie-joelle; Rackham, Brian.
Choice of sampling method and survey period can have an important impact on the perception of the structure and dynamics of an ecological community. For the Celtic Sea fish assemblage we compared data obtained by three different trawl surveys: an autumn groundfish survey with a GOV trawl, and a spring and an autumn groundfish survey, both carried out with a Portuguese high-headline trawl. Time-series of abundance estimates were not consistent among surveys for all species and were generally very noisy. An analysis of variance components showed that the sampling method contributed more to the variance in abundance estimates compared to survey period, interannual variability, or even sampling variance. Overall community assessments based on indicators such...
Tipo: Text Palavras-chave: Trawl; Survey; Species diversity; Size spectrum; Celtic Sea; Abundance.
Ano: 2004 URL: https://archimer.ifremer.fr/doc/2004/publication-899.pdf
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Fishing destabilizes the biomass flow in the marine size spectrum ArchiMer
Rochet, Marie-joelle; Benoit, E..
Fishing impacts on marine food webs are predicted by simulations of a size spectrum community model. In this model, predation is determined by predator and prey size and abundance, and drives predator growth and prey mortality. Fishing amplifies temporal oscillations in the biomass flow. Oscillations appear at lower fishing intensity and have wider amplitude when fishing is selective (removes a narrow size range) and/or when large fish are targeted, than when fishing is more balanced (catching a larger size range) or when small fish are targeted. A novel index of size diversity is developed, and is shown to be sensitive to both fishing intensity and selectivity. To avoid unstable food web dynamics with potential harmful consequences for fisheries, limiting...
Tipo: Text Palavras-chave: Size spectrum; Ecosystem approach to fisheries management; Biodiversity; Fishing selectivity; Community stability.
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00053/16462/14025.pdf
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Fishing effects on diversity, size and community structure of the benthic invertebrate and fish megafauna on the Bay of Biscay coast of France ArchiMer
Blanchard, Fabian; Le Loc'H, Francois; Hily, Christian; Boucher, Jean.
Within the framework of the 'dynamic equilibrium model', we tested the hypothesis that fishing causes major disturbance to benthic communities on deeper bottoms of the continental shelf. Benthic megafauna on the Bay of Biscay coast of France was sampled on fishing grounds subject to various conditions of exploitation. Samples were taken at around 100 m depth to avoid strong natural disturbances. Species diversity and the largest body mass class of invertebrates were smaller in strongly exploited areas than in moderately exploited ones. Biomass size spectra in strongly exploited areas were characterised by a comparatively large biomass of small invertebrates, hence the K-dominance curve of abundance was either above the biomass curve, or the curves...
Tipo: Text Palavras-chave: Benthic communities; Community dynamics; Disturbance; Diversity; Size spectrum.
Ano: 2004 URL: http://archimer.ifremer.fr/doc/00000/10896/7578.pdf
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Fishing effects on the diversity dynamics of demersal fish communities. Comparative analysis of the role of the interactions between specices in the Bay of Biscay and in the Gulf of Lion (France). ArchiMer
Blanchard, Fabian.
This work deals with the fishing effects on the diversity dynamics of demersal fish communities, focusing on the biotic interactions. Multispecies indices were used in order to characterise the demersal fish community dynamics of the Bay of Biscay and of the Gulf of Lions. These are the diversity indices, the temporal variability of the total biomass and of the slope of the number size spectra and the slope of the species-area curves (spatial segregation). The data were provided by yearly bottom trawl surveys EVHOE, CHALIST and MEDITS carried out in these two areas since 1983 by IFREMER for stock assessment. The differences between areas are related to a fishing index (mean value of the annual landings of demersal fish per surface area). Other areas are...
Tipo: Text Palavras-chave: Demersal fish; ANE; Bay of Biscay; Gulf of Lions; Fish communities; Fishing impact; Biodiversity; Biotic interactions; Spatial segregation; Biomass variability; Size spectrum.
Ano: 2001 URL: http://archimer.ifremer.fr/doc/00000/10248/7688.pdf
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How does abundance scale with body size in coupled size-structured food webs? ArchiMer
Blanchard, Julia L.; Jennings, Simon; Law, Richard; Castle, Matthew D.; Mccloghrie, Paul; Rochet, Marie-joelle; Benoit, Eric.
Widely observed macro-ecological patterns in log abundance vs. log body mass of organisms can be explained by simple scaling theory based on food (energy) availability across a spectrum of body sizes. The theory predicts that when food availability falls with body size (as in most aquatic food webs where larger predators eat smaller prey), the scaling between log N vs. log m is steeper than when organisms of different sizes compete for a shared unstructured resource (e.g. autotrophs, herbivores and detritivores; hereafter dubbed 'detritivores'). In real communities, the mix of feeding characteristics gives rise to complex food webs. Such complexities make empirical tests of scaling predictions prone to error if: (i) the data are not disaggregated in...
Tipo: Text Palavras-chave: Size spectrum; North Sea; Macroecology; Ecosystem effects of fishing; Community ecology; Benthic pelagic coupling; Allometric scaling.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-7318.pdf
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Using size-based indicators to evaluate the ecosystem effects of fishing ArchiMer
Shin, Yunne-jai; Rochet, Marie-joelle; Jennings, Simon; Field, John; Gislason, Henrik.
The usefulness and relevance of size-based indicators (SBIs) to an ecosystem approach to fisheries (EAF) are assessed through a review of empirical and modelling studies. SBIs are tabulated along with their definitions, data requirements, potential biases, availability of time-series, and expected directions of change in response to fishing pressure. They include mean length in a population, mean length in a community, mean maximum length in a community, and the slope and intercept of size spectra. Most SBIs can be derived from fairly standard survey data on length frequencies, without the need for elaborate models. Possible fishing- and environment-induced effects are analysed to distinguish between the two causes, and hypothetical cases of reference...
Tipo: Text Palavras-chave: Size spectrum; Size based indicators; Ecosystem approach to fisheries.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/publication-775.pdf
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