LAUSR

Abstract Overfishing has changed the life histories of commercially harvested marine fishes worldwide. The Jamaican weakfish, Cynoscion jamaicensis, which has been caught by trawl fisheries off southern Brazil since the 1950s, was sampled in two periods (1977–80 and 2016–17) to study its life history and changes in growth and sexual maturation and assess its spawning potential ratio. The annual formation of one opaque band on the otoliths was validated, and the oldest sampled fish was a 9-year-old male. Growth patterns did not differ between sexes. The von Bertalanffy growth parameter L ∞ increased with time, and the growth curves were significantly different between periods. Fish of the same age classes were significantly larger, heavier and had higher allometric condition factors in the most recent period than those in the first period. Reproduction occurs seasonally from late spring to early autumn, and the length and age at first maturity decreased between periods. Based on the length distributions obtained in 2016–17, the spawning potential ratio was between 57 and 62%, suggesting a moderate decrease in the abundance of the species in the region. The changes in growth are likely due to density-dependent processes because of the intense fishing that decreased the abundance of the species and of its main competitors. The changes in maturation parameters are more difficult to explain since there are three possible drivers: density-dependent processes and increasing water temperatures for the changes in the age at first maturity and increasing water temperatures and genotypic responses to differential selection for the changes in the size at first maturity. Although C. jamaicensis can be considered a resilient species due to its life history characteristics, the intense biomass removal by fishing in southern Brazil has changed its population dynamics and reduced its spawning potential.