Biomass assessment of the monkfish Lophius gastrophysus stock exploited by a new deep-water fishery in southern Brazil

The monkfish Lophius gastrophysus was the first fishing resource that proved abundant enough to sustain profitable deep-water fishing operations off southern Brazil. As a directed fishery was structured in 2001, a preliminary stock assessment was conducted based on biological samples and catch rate data provided by both national trawlers and chartered gillnetters. Catch-at-size, general linearized models (GLM) and depletion models were combined to provide both pristine biomass and abundance index estimates for 2001. Landing statistics and discard estimates, indicated that fishing removed approximately 10,000 t; 16% of the 62,776 t total biomass estimate and approximately 32% of the spawning stock. Alternatively, GLM abundance indices variation, suggested a more severe 30-60% biomass reduction in the main fishing grounds off southern Brazil throughout 2001. The two fishing fleets have (a) concentrated in different areas and (b) exploited somewhat distinct fractions of the available monkfish stock biomass. Hence, fishing mortality, was concentrated both upon (a) fish larger than 60 cm total length (where F/Z oscillated between 60 and 80%), and (b) most immature 20-60 cm long fish (where F/Z reached 40%). The adoption of a conservative 2500 t total allowed catch (TAC) combined with biological elements was proposed in order to restrict fishing development to precautionary levels. Despite data-limitations and assumptions, the combination of both catch-at-size biomass estimates and abundance indices variation was shown to provide useful elements for fast precautionary management options in a new, poorly known and fragile deep-water Brazilian fishery.