Resgate histórico como ferramenta para reconstruir a abundância passada de tubarões no litoral do nordeste brasileiro

Abstract

Knowing the situation of fish stocks is essential for the management and maintenance of fisheries. However, in Brazil little is known about most stocks, even those of interest to small-scale fisheries. In the absence of this information, historical surveys using interviews with fishers and other groups of people that directly observe fishing resources (e.g., researchers and divers) serve as a tool to evaluate the actual trends of these stocks. Nevertheless, there may be a common distortion associated with this methodology, known as the shifting baseline syndrome. In this syndrome, the informant tends to believe that the moment he or she began to observe the resource, the resource was at its peak of abundance, which disregards past exploitations and can lead to a false perception of the current state of the stocks. One way to alleviate this distortion is to include informants of different ages and experiences, seeking to retrieve the oldest information possible. The general objective of the present research was to do a historical survey of the sighting of some species of sharks by artisanal fishers on the northeastern Brazilian coast, evaluating possible changes in shark occurrences and their sizes along the last six decades, using for that information provided by artisanal fishers. The data were collected along part of the northeastern coast (states of Rio Grande do Norte, Paraíba, Pernambuco and Bahia). Out of the eight species analyzed, in three (Carcharhinus leucas, Ginglymostoma cirratum and Sphyrna lewini) the fishers perceived a decreased in their maximum size over the years. Coastal species were the most likely to suffer from these size variations. The different groups of fishers, classified into age groups, had different perceptions of the average sizes of the species Carcharhinus leucas and Isurus oxyrinchus. With the ever-increasing risk of extinction of large predators, we hope to contribute to the understanding of the patterns of abundance and size changes of fish and their stocks over the recent past through the knowledge accumulated by fishers.