Utilization of aquatic resources along the North Brazilian coast with special reference to mangroves as fish nurseries.

Abstract

Abstract The coastline of Brazil stretches approximately 8400 km, with a continental shelf area of 822,800 km2 and a declared exclusive economic zone of approximately 4.5 million km2. Mangroves are the dominant coastal vegetation, particularly in the north of the country, covering an area of 13,400 km2, accounting for 8% of the global mangrove cover. Common marine fish include sardines, corvinas, snappers, croakers, tunas, lobsters and shrimp. In 2005, 750,000 t were landed, including 60,000 t of molluscs and crustaceans (predominantly shrimp). Fishing is practised on both a small scale and an industrial scale. Fish production has decreased from about 1 million t to the low current numbers in the past two decades, an indication of the overexploitation of these resources. Long-term management plans are urgently required, taking into consideration the life cycles of the fish, to guarantee sustainable utilization of the resources by the local population. Juveniles of many marine fish species use estuarine nursery habitats before moving as adult populations to the coastal waters. However, data on numbers of individuals from the exploited populations, which spend their early life in the different estuaries, are lacking. Thus, it is not known whether all estuaries contribute equally to maintaining local stocks or if adult stocks in the coastal waters rely on recruitment from only one estuary or a number of estuaries. This question has significant implications for coastal management and land-ocean exchange processes. Connectivity studies, using biogeochemical signals on fish otoliths, will contribute to our understanding of the relationships between populations of marine and estuarine fish species and their population dynamics, and will help to distinguish between open and closed populations, information which is essential for stock assessment purposes and the design of marine and coastal protected areas. The findings will help clarify if the different estuaries are habitat patches inhabited by metapopulations. As human activity continues to impact and eliminate natural habitats, the mangrove forest being a prime example, understanding the spatial connectivity between juvenile and adult populations becomes increasingly important. Connectivity is likely to depend not only on the distance between the habitats of two life-history stages, but also on the presence of movement corridors or stepping stones of natural habitats.