Effects of exploitation by two co-existing fleets on the bluefish, Pomatomus saltatrix, in southern Brazil: an application of a seasonal catch-at-age model

Abstract

This paper describes 20 years in the exploitation of the bluefish, Pomatomus saltatrix, in southern Brazil and investigates the effects of the commercial fleets on stock structure. Port samples were obtained from the commercial fisheries based at Rio Grande do Sul for the period 1992–1998. In addition, data derived from the exploitation during the period 1977–1983 (Krug and Haimovici 1991) were included in this analysis. A statistical catch-at-age model is proposed to estimate population size and exploitation rates for both periods of study. This model incorporates both the seasonal characteristic and multi-fleet nature of the P. saltatrix fishery. During the most recent time period, fishery mortality has increased and spawning stock biomass has reduced in comparison to the earlier period 1977–1983. Currently, the exploitation of P. saltatrix relies on fish of all age classes. Adults have been intensively exploited and juveniles may not be abundant enough to maintain the stock at the current high level of exploitation. Management options for the stock are presented based on a redistribution of effort between fleets. Simulations indicate that a ban on fishing in shallow waters for either one or both gears would restore the level of spawning stock biomass.