Geoff J. Meaden

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.

Geographical Information Systems (GIS) in Fisheries Management and Research

Geographical Information Systems (GIS) may be defined as a collection of computer hardware, software, data and personnel designed to collect, store, update, manipulate, analyse and display geographically referenced information (Rahel 2004). As a tool for terrestrial spatial analysis, GIS functionality first developed in the 1960s. This development occurred in Canada, emerging here as a result of the convergence of various needs and capabilities, e.g. a large spatial area having a rich resource base; insufficient capacity to map and record resource distribution by old cartographic means; developments in computing and computer graphics and computer assisted design; plus a number of individuals with a vision of how cartography might be automated and applied. During the 1970s considerable resources were put into further research into computer mapping by institutes such as Harvard University with their SYMAP initiative, plus GRID and GEOMAP (Tomlinson 1989). The 1980s were chiefly characterised by the move into GIS of the first private commercial software developers who could appreciate the great potential of this technology. Since the early 1990s GIS has continued to grow at an average compound rate of about 14% p.a., and sales world-wide today of GIS related hardware and software are measured in billions of dollars, with unquantified data sales on top of this. Most of this GIS success has been manifest in terrestrial applications. With the planet becoming an ever more crowded arena in terms of sourcing human needs, then ‘‘conflicts’’ over access to, and use of, space has become ever more prevalent. Conflict requires management and management requires decision making, and this is where GIS comes into its own. In almost all spheres of human activity GIS is now playing a useful role. Early GIS applications were mostly in the public domain in areas such as forestry, the emergency services, in public health and utilities, and in the defence arena, but now applications and use by private companies has probably equalled or overtaken public domain