Long term changes in the sexual maturity and in the reproductive biomass of the southern king weakfish Macrodon atricauda (Günther, 1880) in southern Brazil

The coastal demersal sciaenid fish “pescadinha” Macrodon atricauda has been intensely fished along southern Brazil in the last 50 years, a fact that resulted in the decrease in its abundance, maximum age and landings, and an increase in its growth. In this study, we used data from four discrete time periods between 1976 and 2011 to analyze the possible influences of fishing on the maturation parameters length (L50, mm) and age (A50, years) at first maturity as well as on the spawning biomass. Results indicated that the L50 of females and males decreased approximately 30 mm and the mean A50 of females was reduced from 2.2 to 1.6 years. The most plausible explanation is that these changes occurred by the harvest selective pressure of fishing implying lower fitness for individuals that mature at larger sizes. However, there is some evidence suggesting that the A50 may also have been driven by the decrease in the population abundance which relaxed density dependent effects responsible for delaying maturation. If constant recruitment is assumed, the increase in fishing effort and, hence, total mortalities, should have reduced female spawning biomass to 13% of the virginal biomass; however, increased growth rate and earlier maturation resulted in a reduction to only 28%. Reduced spawning biomass combined with a decrease in the reproductive potential of the population (changes in A50 and/or L50), can make recruitment more vulnerable to environmental drivers and to any further increase in the fishing effort.