Evidence of difference in landings and discards patterns in the English Channel and North Sea Rajidae complex fishery

Abstract

Bycatch species such as skates and rays are for most of them not subject to analytical stock assessment. However, their life history characteristics increased their vulnerability to fisheries. In the English Channel and North Sea area, the three main landed Rajidae species are Raja clavata, Raja brachyura and Raja montagui. The current management measure is a global TAC, common for all Rajidae species. Data to process analytical stock assessment are not available for these species, particularly discards data. A Bayesian multispecies biomass production model, following separately the landings and discards was applied to these stocks. This model provided proxies of reference points (MSY and BMSY) per species. All stocks were depleted in 1990 and are now rebuilding. However, rebuilding speeds are different within the complex, R. clavata being the fastest and R. brachyura the slowest. Furthermore, the proportion of the discards and landings to biomass differ between species, highlighting species specific fishing strategies. Differences in vulnerabilities within the Rajidae complex might be caused by the variability of life history parameters between species as well as landings and discards pattern differences. This second factor, usually not considered for data limited stock assessment, is particularly relevant for highly discarded chondrichthyans species, and might be considered when choosing new methodology to asses Rajidae stocks.