Aspects of the population structure of the brown mussel, Perna perna, related to the extraction from natural beds, of Santos Bay, State of São Paulo, Brazil

Abstract

The brown mussel, Perna perna (Linnaeus, 1758), from natural beds of Santos Bay, State of São Paulo, Brazil, has been studied aiming the evaluation of the population structure through the analysis of its length frequency distributions. Data have been obtained from four areas inside the Bay: Saco do Major, Palmas Island, Paranapuã Beach and Fort Itaipu. The results show that the brown mussels from beds of the eastern side of the Bay (Saco do Major and Palmas Island) are larger than those from beds of the western side (Paranapuã Beach and Fort Itaipu), and that the gatherers intensively exploit mussel beds. It was observed that the extraction rate in the eastern side beds is lower, due to, possibly, the higher exposition of them to the waves, which difficult the access to these beds. Questionnaires were applied to local communities, in order to know the value of the annual extraction rate, so as the profile of the population involved in mussel extraction. With the data presented, the mussel extractors could be divided into two groups. The larger group lives in a so called locality of Santa Cruz dos Navegantes, and its integrants work chiefly as fishermen, complementing their incomes with the mussel extraction. The second group, which is less organized, is mostly constituted by unemployed men, without fishing background or skills. The estimated annual production of the two groups of gatherers (forty-seven extractors) was 364 metric tons. The results of the study suggest that the exploitation of P. perna mussel in Santos Bay is near to its maximum limit. Then, such exploitation should be replaced by a medium-term establishment of musselculture in commercial scale, with the accomplishment of recent legal measures of restriction, which assures the sustainable exploitation of natural beds, both for seed production and for adult mussel extraction.