Exploração das áreas entre-marés pela população humana no saco da Ilha de Inhaca

Abstract

The work was carried out in Inhaca Island, between January and March 1995. Surveys were made on the captures of benthic invertebrates made by the human population in the Saco da Ilha, for the identification of the species collected, determination of the fresh weight per species and sizes of individuals during dead and live tides. Surveys were also carried out to determine the relative value of the species assigned by the population of the Island and 4 ladies were followed at high and low tide to study their capture method, which was recorded with a portable computer using the Observer programme. A total of 23 species of benthic macroinvertebrates are exploited, where a dominance in biomass, of crustaceans over gastropods and bivalves is observed. The population captures a greater number of species at dead tide. About 90.63 g of fresh weight /ha/day are exploited at high tide. Of this total, the crab Portunus pelagica, accounts for 71%. On dead tide, people exploit 98.79 g (fresh weight)/ha/day. The crustaceans Uca spp, Scylla serrata and the gastropod Polynices mamilla, contribute 25, 20 and 19%, respectively. As for the ash-free dry weight (AFDW), it is 11.17 g /ha /day on the high tide and 10.38 g /ha /day on the low tide. Although higher amount of fresh weight is exploited in the dead tide, it is in the alive tide that higher ashless dry weight (AFDW) is verified, which shows the great profitability of the species harvested in the alive tide. During high tide, the population specialises in catching the crab Portunus pelagica and harvests species of larger size and higher profitability (% of AFDW in fresh weight), except for the crab Scylla serrata which is more available at dead tide. Of the species harvested, the population considers Scylla serrata to be the most important, followed by Portunus pelagica, Anadara natalensis and Cardium flavum. The simplest animals to catch are the molluscs and the most difficult are the crabs Scylla serrata and Thalamita crenata. The pattern of human exploitation is understood through the importance of the species in combination with the different availability at high and low tide. We agree with the hypothesis formulated that the human population during high tides is more selective (choosing fewer species, but larger size and biomass) than during neap tides. (TRADUÇAO NOSSA)