Life history, population dynamics and stock assessment of the bycatch species Brazilian flathead (Percophis brasiliensis) in southern Brazil

Abstract

The life history and population dynamics of the marine demersal bony fish Percophis brasiliensis were studied to assess its stock status in southern Brazil. Specimens were sampled from commercial landings, and the length, weight, sex, and maturity stage were recorded from each individual. Sagittal otoliths were removed for aging, and the gonads were weighed for maturity studies. Size compositions were also evaluated from commercial landings of different fishing fleets. The analysis of edge type validated the aging data. The oldest and largest individuals were 12 years and 718 mm in total length, respectively. Growth parameters fitted to the von Bertalanffy model were L∞=625.0mm, k 0.39 year−1, t0=−0.26 years for females, L∞=573.4mm, k = 0.34 year−1, t0= −1.13 for males and L∞=617.6mm, k = 0.33 year−1t0= −0.82 for both sexes. The length and age at first maturity of females were 407.7 mm and 2.2 years, respectively. The reproductive season was estimated to occur during spring from September to December, with a peak in October. The life history parameters and the reproductive season described in this study are similar to those estimated by other studies on southern stocks fished in Uruguayan and Argentinian waters. The estimated population trends presented a steady decrease between 1986 and 2005, a slight increase from 2005 and 2010, and a sharp decline until 2019. The stock status was estimated as overfished but not suffering overfishing. Despite not being a target species, the biomass decline trajectory of Percophis brasiliensis reflects intense targeting of other bottom trawl species in the same depth range. These results highlight the importance of life-history studies and continuous monitoring of species impacted by fisheries. Their depletion may affect the functional relationships in marine ecosystems and threaten the resilience of populations to stochastic effects such as climatic variations.