Seasonal dynamics and yield in a tropical coastal fishery in northeast Brazil

Background/Question/Methods

Fishery yield is frequently related to seasonal variation in temperature. However, there is much less seasonal variation in temperature in the tropics and it is therefore important to explore the effects of other variables on richness and relative abundance of tropical fsh assemblages. Here, we test whether seasonal patterns of rainfall and wind influence the structure of a tropical coastal fish assemblage exploited by an artisanal gillnet fishery. Three samples were taken with bottom gillnets during the rainy season and three during the dry season. Two environment variables were recorded: 1. Mean wind speed (m/s); and 2. Monthly precipitation sum (mm). Diversity was analyzed by Whittaker curves of abundance, diversity profiles and the Shannon index. Principal Component Analysis (PCA) was used to analyze the relationship of the more abundant species with environment variables. 

Results/Conclusions

A total of 2,373 fish, belonging to 73 species from 34 families were collected. The Whittaker diagram indicated that the rainy season assemblage is richer and more equitable than the dry season. The diversity profiles did not differ between rainy and dry seasons (P>0.5). The number of species, number of individuals, CPUE and mean length were significantly higher in the rainy season (P<0.05 to each analysis). The PCA identified three species groups: one group mainly related to wind speed; another related to dominant species of the rainy season, and a ‘mixed’ group related to high rainfall and wind speed, or waters of high turbidity. We conclude that seasonal effects of rainfall and wind in tropical areas can modulate the structure of coastal fish assemblies and yields of fisheries using bottom gillnets.