Long-term targets for the Celtic Sea mixed-species multi-métiers fisheries

Abstract

A deterministic, forecasting, equilibrium study has been conducted of the multispecies and multi-métier fisheries of the Celtic Sea, ICES divisions VIIf and g. Calculations have been made of the optimal fleet sizes and mesh sizes required to maximize objectives of joint relative sustainable yields, gross revenue and net revenue. The species modelled are the resident populations of cod (Gadus morhua), whiting (Merlangius merlangus), sole (Solea solea), plaice (Pleuronectes platessa) and Norway lobster (Nephrops norvegicus), with additional consideration given to catches of hake (Merluccius merluccius), monkfish (Lophius sp.) and megrim (Lepidorhombus whiffiagonis). The fleet métiers modelled are the beam trawls, Nephrops otter trawls and non-Nephrops otter trawls. If mesh sizes can be calculated independently foreach métier, then the yields and the gross revenue are maximized by increased effort and mesh sizes, especially in the non-Nephrops fleet. If a common mesh size is required for all fleets, then the yields and the gross revenue are maximized when (i) this mesh size is of 114 mm, (ii) the fishing effort in beam and Nephrops fleets is significantly increased, (iii) the non-Nephrops fleet is almost eliminated. Maximization of net revenue requires a mesh size similar to the current mesh of 80 mm, but with significant reductions of fishing effort in all fleets. Average profitability is increased by 50 millions EUROs per year for the Celtic Sea fishery. The model provides a basic structure for examining the management with a more realistic dynamic and stochastic description of the Celtic Sea fisheries.