Appraisal of the selective properties of gill nets and implications for yield and value of the fisheries at the Itaipu Reservoir, Brazil-Paraguay

We studied the selective properties of gill net mesh-sizes used in the fish eries at the Itaipu Reservoir to assess the likelihood of growth and recrui tment overfishing, and to explore modifications of current harvesting appro aches and their effect on the fish stock and the value of the fishery. We u sed empirical growth estimates and gill net selectivity to model yield per recruit, size distributions, value per reemit, and spawner biomass per recr uit under different natural mortalities, fishing mortalities, and gill net mesh-size restrictions. Our results suggest growth overfishing may be limit ing fishery yield and commercial value. Increasing mesh-size (in most cases ) and increasing fishing effort (in some cases) would lead to higher yields and commercial values. Nevertheless, such increases would further reduce t he biomass of the spawning stock, and we could not predict whether such red uctions would lead to recruitment overfishing, nor their effect on the inte ractions between the fishery species and the associated fish assemblage. Ho wever, we identify how fishing effort and mesh-size may be juggled to boost yield and commercial value without reducing current biomass of the spawnin g stock. Published by Elsevier Science B.V.