Fishery catches on the Lower Amazon River were analyzed in relation to the hydrological cycle, temporal shifts in fishing effort, and the use of nets or lines in lakes and rivers. The study was based on a temporal series of catch data collected between January 1993 and June 2011. The variables analyzed were the total catch, use of gillnets or lines, the environment targeted (lakes or rivers), and fishing effort. Temporal trends in the data series were analyzed using the Mann–Kendall test. An Analysis of Covariance (ANCOVA) was used to evaluate whether gillnet and line catches had independent effects on the catch data. Duncan’s test was applied to identify the groups (months) of means that were significantly different from each other. The majority of the catch landings were taken with gillnets (98.65%) in a lake environment (64.98%). The temporal series showed a significant decline over time in the gillnet catches from both lakes and rivers, as well as in fishing effort. The influence of the annual flood cycle was reflected in the catches and the flood pulse regulated fishing productivity patterns in the region. The fishers who adapt their activities to this flood pulse have good traditional knowledge of the environment. The results of the study also indicated that any changes in this dynamic system may impact traditional local fisheries and affect the economic wellbeing of local fisher populations.

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.