Inferences about Fishing Impacts on the Reproductive Pattern of Torroto Grunt—Genyatremus luteus (BLOCH, 1790)—From the Amazon Continental Shelf

Abstract

Genyatremus luteus’ reproductive dynamics were investigated by examining the gonadal first maturation length (L50) and reproductive period (gonadosomatic index, GSI, and relative condition factor, Kr) in relation to the environmental factor rainfall. Sampling was conducted monthly from April 2016 to April 2017, in five areas (A1 to A5) using gill nets and fixed traps. The sex ratio distribution of the 331 specimens captured (174 females, 140 males, and 17 with undetermined sex) did not differ between months. Females were larger (19.28 cm vs. 16.63 cm to males) and heavier (147.21 g vs. 92.14 g to males) and, for both sexes, the means of Kr and GSI indicated the probable spawning period of the species that occurred from June to September, after a decrease in the precipitation of the region. The value of L50 was estimated as 15.13 cm for females, 14.29 cm for males, and 14.78 cm for both sexes. In the rainy season, the behavior of the species is associated with breeding in certain areas but in the dry season, it is related to the fattening and refuge of juveniles and adults. This research shows the first insight for fishing management about a species that requires different ecosystems to complete their life cycle.