Interpretando os efeitos antrópico-ambientais na ictiofauna ao longo dos habitats costeiros e marinhos no Nordeste do Brasil

Abstract

Changes in coastal ecosystems through fishing or other anthropic impacts represent a major threat to the conservation of many species that depend on the complementarity and proper functioning of different coastal ecosystems (mangroves, reefs, marine prairies). This study aimed to document some of the impacts suffered by the succession of interconnected coastal habitats in Pernambuco. Thus, this thesis was divided into two parts. The first part addressed activities that had a physical impact on the connected marine landscape. Hence, satellite data from the coastal landscape has been collected over the past three decades to provide information on the evolution of mangrove cover in three estuaries of Pernambuco. In addition, stable isotope methods have been employed to understand the variability in ecological connectivity between estuarine and coastal habitats in the context of increasing anthropogenic changes in estuarine morphologies. We investigated the influence of this morphology on the flows between morphologically distinct estuaries and their adjacent coastal areas by tracing the origin of organic matter (coastal or estuarine) underlying the diet of the silver mojarra Eucinostomus argenteus. The results of this first section show that although anthropic activities (aquaculture, agriculture, urbanization, and port construction) have caused mangrove swamps to be deforested, there is a tendency to increase their total coverage in two of the three estuaries studied over the past three decades. This has been related to salinization, allowed by climate change and other anthropic activities (port, dams). We observed that the morphology of the estuaries could influence the diet of the silver mojarra, causing the contribution of the coastal resources to the diet to increase with the connection with the sea (determined by morphological characteristics such as mouth width). Thus, activities established along the coast of Pernambuco are modifying the maritime landscape by removing habitats such as mangroves and are affecting the functioning of ecosystems by modifying environmental variables, influencing flows between connected habitats and inducing salinization. The second part of the thesis was related to the impact of coexisting fleets that exploit these connected environments. For this purpose, the catches of the main fishing gears operated along the estuary-shelf gradient were examined. Our study showed that the complex fishing pattern of the different coexisting fleets results in the capture of migratory species by various fishing gears along the estuarine-platform gradient and at different life stages. The various fishing gears have mostly caught productive compartments (young individuals and low trophic species). As the co-existing fleets target common species, the incomes of these fisheries are co-dependent, making multi-ecosystem management necessary. Our results suggest that size limitations would not be enforceable on these co-existing fleets, because the income benefits will not be obtained by the fleets that would suffer from these limitations. An ecosystem-based approach such as "Balanced harvest" (the idea of fishing a variety of species, stocks and sizes in proportion to their natural productivity), consistent with existing fishing patterns, could be an interesting alternative for managing these fleets. As fishing activity occurs in degraded habitats, marine spatial planning would then be of paramount importance for the management of these fisheries. This planning should integrate all activities that may cause damage to coastal and marine habitats because fisheries yields require the proper functioning of these connected ecosystems.