Population structure and average length at the first maturation of the king weakfish, Macrodon ancylodon (Bloch & Schneider, 1801) (Pisces, Sciaenidae) in the estuarine complex of São Marcos Bay, eastern amazon, Brazil

This study aimed to describe aspects of the composition and population structure of this species, captured with the use of fixed gillnets in quarterly samples during the period February 2014 to November 2015, within the estuarine complex of the bay of Sao Marcos - MA. In laboratory total length, total weight and macroscopic analysis of gonads. We analyzed 195 specimens of M. ancylodon distributed in 20 males and 175 females. The individuals examined ranged from 9.80 cm to 40.10 cm in total length and 7,93g to 515,65g in total weight. The population structure showed a higher incidence of capture (54.36%) in the class interval of 25.8 cm to 29.8 cm. The species showed negative allometric growth, with a significant difference between the sexes. The sex ratio showed a predominance of females, especially in the upper total length classes. The condition factor indicated the highest peak from May to August and the lowest from November to February. The L50 was estimated at 19.69 cm to 21.97 cm for males and females. The large percentage of individuals into mature stages found in the estuarine complex of the bay of São Marcos infer to an extended period of spawning and justifies the breeding ecological relevance of this environment. The parameters presented in this research must be taken into consideration for the management of this resource, considering the high level of exploitation of the species by artisanal fishing carried out on the coast of Maranhão.