Highly mixed fisheries: fine-scale spatial patterns in retained catches of French fisheries in the Celtic Sea

Abstract

Efficiency of mixed-fisheries management and operational implementation of the ecosystem approach to fisheries management rely on the ability to understand and describe the technical and biological interactions between fleets, gears and species. The present study aims to describe fine-scale spatial patterns of the French demersal mixed fisheries in the Celtic Sea and discusses their implications in terms of management. Analysis was made by integrating vessel monitoring systems and logbook data collected between 2010 and 2012 at a 3′*3′ spatial scale through the use of principal component analysis followed by hierarchical clustering. It revealed spatial regions defined by a distinct homogeneous composition of retained catches. Each cluster was also described in terms of the fishing activity: vessel length, effort, power and gear used. The analysis revealed a complex spatial structure in the species assemblage caught and suggests that a single situation cannot describe the mixed fisheries of the Celtic Sea, but rather that there are several distinct cases of mixed fisheries. Our results also highlight the limitations of using the current level of data aggregation commonly requested in international data calls to model these fisheries and suggest that improvements should be made to ensure efficient evaluation of management options. Analyses of spatially resolved fisheries data such as the one presented here open a range of potential applications. In the context of the Common Fisheries Policy reform and the landing obligation, comparison of our results with applications of the same methodology to a subset of vulnerable species or to catches of fish below the minimum conservation reference size would help to identify the geographical areas to avoid and assess potential effort reallocation strategies based on groups of target species.

Environment outweighs the effects of fishing in regulating demersal community structure in an exploited marine ecosystem

“…The Celtic Sea is also an important fishing zone, intensively exploited by France, Ireland, the UK, Belgium, and Spain since at least the 1950s (Guénette & Gascuel, 2012). It sustains an important fishery of more than 100 species, from algae to top-predator fishes (Mateo, Pawlowski, & Robert, 2017). After major changes occurred in the 1950-1970, a decreasing trend of fishing mortality has been reported since the mid-1990s for assessed benthic and demersal stocks (ICES, 2018b).…”

“…Previous studies in the Celtic Sea described communities in relation to fishing and oceanographic variables, at relatively local geographical and temporal scales, around the banks in the center of the Sea (Martinez, Ellis, Scott, & Tidd, 2013;Mateo et al, 2017;Sharples, Ellis, Nolan, & Scott, 2013). However, the question of their long-term and large-scale variability remains to be addressed.…”

Spatial distribution of discards in mixed fisheries: species trade-offs, potential spatial avoidance and national contrasts

“…The objective of the analysis was to identify and describe areas with similar discard profiles, using a combined set of multivariate methods (principal component analysis (PCA) and hierarchical classification) as described in (Mateo et al 2017).…”

“…In some case, matching was difficult illustrating structural differences in the data between the eight case studies. The spatial distance between the grid cells was not taken into account, so any spatial patterns that emerge from the analysis are the result of similarities in the discard composition of neighbouring cells (as in Gerritsen et al, 2012;Mateo et al, 2017).…”

“…The area accommodates a high diversity of marine species that support fisheries targeting different species assemblages from pelagic to demersal (Gerritsen and Lordan 2011;Martinez et al 2013;Mateo et al 2017;Dolder et al 2018). The mixed nature of these fisheries leads to high discard rates, especially in the mixed demersal trawl fishery where many species occupy similar habitats and display similar behaviours making it difficult to selectively fish for individual species.…”