Biomass dynamics of the squid Loligo plei and the development of a small-scale seasonal fishery off southern Brazil

The squid Loligo plei, has been an important component of the trawl fishery by-catch in Santa Catarina State, southern Brazil (26°S) and has, in recent years, motivated directed inshore and offshore small-scale fisheries. The structure and dynamics of this fishery have been studied since 1995 from Brazilian government landing statistics (1989–1997) and from a fishery sampling program developed in the Itajaí harbor and coastal fishing communities. Both offshore and inshore catches are concentrated in the summer months. Offshore fisheries have been conducted by double rig trawlers and pair trawlers on the northern shelf between the 20 and 45 m isobaths. Whereas only part of shrimp trawlers and fish trawlers have directed each summer their effort towards squid, almost all pair trawlers have targeted exclusively for squid. Pair trawlers have produced most of squid catch since 1993 and have gradually increased their contribution to the total effort directed at squid. CPUE (Catch per Unit of Effort) variation during the summer indicated that catches have been sustained by an annual cohort that becomes available in December and disappears in March, reaching a main biomass peak within this period. Fish and pair trawlers tended to direct their effort at biomass peaks. The trawling fishery effort directed at squid during the summer has been associated with a biomass decrease since 1993, with pair trawlers bearing the main responsibility for this impact. A Leslie extended depletion model was found to be a promising tool for estimating L. plei biomass available for fishing each season and the proportion of escapement.