Abstract
<title>Abstract</title> <p> The present study uses the fish community as an indicator of biodiversity in the estuary of Coqueiros Strait on São Luís Island, state of Maranhão, Brazil, which is a region under the influence of port activities. Six collections were performed at four sampling points between February 2022 and June 2023. Fishes were caught by artisanal fishermen using fixed gillnets, with a six-hour standardized fishing effort. After capture, the fishes were transported to the laboratory for taxonomic identification, biometric measurements, and weighing. A total of 8,063 individuals of 47 species belonging to 28 families were caught, with a predominance of the orders Siluriformes (28.79%) and Perciformes (22.68%). The species <italic>Sciades herzbergii</italic> had the highest relative abundance (25.5%). Species diversity varied over time, with the highest values in June 2023 and lowest in February 2022. The Shannon-Wiener diversity index (H') ranged from low (H' = 1.98 in February 2022) to medium (up to H' = 2.61 in other periods), while evenness exhibited spatial and temporal fluctuations. Sampling point P1 had greater uniformity in the distribution of the species, while P2 and P3 had greater similarity to each other. Diversity ranged from low (Feb 2022, H' = 1.98) to medium (other months, up to H' = 2.61), with evenness also fluctuating over time and space. P3 has the lowest diversity and evenness, suggesting a greater dominance of opportunistic species, while P1 and P4 had more balanced communities. The analysis of the ABC curves corroborated these results, indicating relatively more preserved environments at some points and greater anthropogenic pressure at others. The results indicate that the composition and abundance of the ichthyofauna are mainly influenced by seasonal factors, with variations in the structure of the communities over time. Despite the proximity to port activities, no significant changes were found in the ecological indices analyzed. This study highlights the importance of the estuary Coqueiros Strait as a nursery and feeding area for several fish species, underscoring the need for continual monitoring and sustainable management strategies of fishery resources to ensure the conservation of biodiversity and food security for local populations. </p>