Andre Carpentier

Estimating limits to the spatial extent and suitability of sole (Solea solea) nursery grounds in the Dover Strait

There is a growing need for accurate and interpretable maps that describe the spatial extent and suitability of flatfish habitats. A common approach to developing such maps is to construct spatially explicit habitat models from fisheries-independent survey data. As the entire range of factors that define fish habitats can never be fully quantified, habitat models are invariably built from a small subset of factors, which typically consist of physical seabed and water column characteristics. If important physical and biological habitat features have not been measured, conventional modelling techniques may underestimate habitat use and quality. We present a spatial modelling technique capable of estimating the maximum extent and suitability of flatfish habitats, i.e. the potential or upper limits of the habitat, using juvenile sole (Solea solea L.) in the Dover Strait as an example. To develop the models, juvenile sole catch densities and environmental habitat data were first acquired and assembled within a Geographical Information System (GIS). Regression quantiles were then estimated for models of change in juvenile sole catch density according to changes in a number of habitat variables. Finally, spatial models were constructed within a GIS by combining the quantile regression models with digital maps of the environmental variables. The use of regression quantiles allowed linear model parameters to be estimated near to the upper bounds of the sole-habitat relationships, thereby providing estimates of the limiting effects of the habitat. In turn, the habitat map built from the upper regression quantiles provided robust estimates of the maximum spatial extent and suitability of sole nursery grounds in the Dover Strait region, as confirmed by model tests using independent data. Habitat maps developed using this approach may be desirable from a species conservation perspective, as the likelihood of underestimating the extent and quality of the habitat is reduced.

Morphological variability of the shape of striped red mullet Mullus surmuletus in relation to stock discrimination between the Bay of Biscay and the eastern English Channel

Truss analysis and length measurements were made on 168 striped red mullet Mullus surmuletus. Multivariate statistical analyses with principal component analysis and partial redundancy analysis (pRDA) were used on these measurements to evaluate the influence of maturity, sex and geographical area distribution on body shape. Truss measurements were important to quantify and discriminate changing body shape, presumably due to changing environmental conditions. Sexual dimorphism was not observed and juveniles could be distinguished from adults based on their body shape. More importantly, M. surmuletus occurring in different geographical areas could be differentiated using this method. Based on pRDA, a significant difference of head morphological dimensions was observed between populations occurring in the eastern English Channel and those occurring in the Bay of Biscay, suggesting that fish from these areas could represent two subpopulations.

The Channel Programme: A Large-Scale Integrated Approach

The Channel programme is a collation of interlinked multidisciplinary projects supporting ecosystem-based management in the English Channel by integrating works carried out in the past thirty years including novel approaches to the spatial modelling of ecosystems. The Channel programme has required a coordination of efforts and expertise by both scientists and stakeholders to address the challenges of the Marine Strategy Framework Directive and of its national implementations. The Channel programme has also consisted of harmonising information, regulations and habits in terms of ecosystem management in the English Channel.