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Mackinson S.,CEFAS - Center for Environment, Fisheries and Aquaculture Science
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2014

When an ecosystem model of the North Sea is calibrated to data from multiple trophic levels, the model estimated the primary production required to support the food web correlates temporally with observed changes in sea temperature and nutrient levels, supporting evidence from empirical analyses. However, a different result is given from an alternative calibration using fish stock data only. The inference taken from the emergent primary production - temperature relationship and empirical data are that, on balance, there is stronger overall evidence to support the calibration constrained at multiple trophic levels. Two important implications of the findings are (i) that the relative importance of fishing and environmental effects is likely to be interpreted differently depending on the calibration approach and (ii) the contrasting model calibrations would give different responses to fishing policies. It raises questions regarding how to judge the performance (and credibility) of an ecosystem model and the critical importance of conducting empirical and modelling analyses in parallel. Adopting a combined approach to ecosystem modelling is an important step in the pursuit of operational and defensible tools to support the ecosystem approach to management. Source

Law R.J.,CEFAS - Center for Environment, Fisheries and Aquaculture Science
Marine Pollution Bulletin | Year: 2014

In this article I review recent trends reported in the literature from 2008 to date for organic contaminant concentrations in marine mammal tissues worldwide, in order to get an idea of where we stand currently in relation to the control of hazardous substances. For many contaminants which have been subject to regulation regarding their production and use (e.g. organochlorine pesticides, PBDE and HBCD flame retardants, butyltins) trends are downwards. For perfluorinated compounds, trends are more mixed. For dioxins, furans and dioxin-like CBs, there are no recent data, for either concentrations or trends. For CBs overall, earlier downward trends in concentration in UK harbour porpoises following regulation beginning in the 1980s have stalled, and remain at toxicologically significant levels. This raises concerns for killer whales and bottlenose dolphins who, because of their larger size and greater bioaccumulation potential, have higher levels still, often far above accepted toxicological threshold values. © 2014 . Source

Copp G.H.,CEFAS - Center for Environment, Fisheries and Aquaculture Science | Copp G.H.,Bournemouth University
Fish and Fisheries | Year: 2010

Originally developed to assess the relative abundance of ≥1+ fishes in large rivers, point abundance sampling by electrofishing (PASE) was adapted for 0+ fishes in the mid-1980s. Being both economical and widely applicable, PASE for 0+ fish has become a commonly used sampling approach in Europe, but its use for estimating 0+ fish density and species richness has attracted particular concern because of size and species selectivity. As such, this review is both timely and necessary. It summarizes the development of PASE and evaluates its various applications: studies of 0+ fish community composition, relative abundance and density, species richness (S), population size structure, larval and juvenile growth dynamics, microhabitat use, diel dynamics of species-species and species-microhabitat interactions, and the analysis of data emanating from PASE databases. The use and potential misuse of replicate sampling in estimates of S are examined, with PASE data from various European rivers re-analysed to assess geographical patterns in 0+ fish S. Comparisons of PASE and other approaches for estimating 0+ fish density and species richness have all demonstrated PASE to be cost-effective and relatively reliable, but sampling accuracy and precision do decrease as fishes enter the juvenile period of development. © 2010 Crown copyright. Source

Rossberg A.G.,CEFAS - Center for Environment, Fisheries and Aquaculture Science | Rossberg A.G.,Queens University of Belfast
Advances in Ecological Research | Year: 2012

The prediction and management of ecosystem responses to global environmental change would profit from a clearer understanding of the mechanisms determining the structure and dynamics of ecological communities. The analytic theory presented here develops a causally closed picture for the mechanisms controlling community and population size structure, in particular community size spectra, and their dynamic responses to perturbations, with emphasis on marine ecosystems. Important implications are summarised in non-technical form. These include the identification of three different responses of community size spectra to size-specific pressures (of which one is the classical trophic cascade), an explanation for the observed slow recovery of fish communities from exploitation, and clarification of the mechanism controlling predation mortality rates. The theory builds on a community model that describes trophic interactions among size-structured populations and explicitly represents the full life cycles of species. An approximate time-dependent analytic solution of the model is obtained by coarse graining over maturation body sizes to obtain a simple description of the model steady state, linearising near the steady state, and then eliminating intraspecific size structure by means of the quasi-neutral approximation. The result is a convolution equation for trophic interactions among species of different maturation body sizes, which is solved analytically using a novel technique based on a multiscale expansion. © 2012 Elsevier Ltd. Source

Although the impacts of dredged material disposal in the marine environment have been well studied, there is currently a limited understanding of the associated impacts on benthic function. This study compares macrofaunal structural and functional (based on secondary production estimates) responses to dredged material disposal at 14 sites across the coast of England and Wales.Disposal resulted in significant reductions of total secondary production at seven sites; no sites exhibited significant increases in production estimates. These seven sites were generally those which displayed significant structural impacts. There was no clear relationship between multivariate structural changes and taxonomic contribution to total production, indicating that a lack of change in the former (regarded as a sensitive indicator of change) does not always signify a lack of a significant functional impact. The need to evaluate functional changes, in addition to structural impacts, with respect to dredged material disposal site monitoring is discussed. © 2012. Source

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