Aspectos biológicos ligados à produtividade da pesca nos açudes públicos da área do "Polígono das Secas" - nordeste do Brasil
Study on fishing productivity of some reservoirs in the area of droughts of northeast region of Brazil, correlated with the influence of number of occurences of carnivorous fishes within the same. The data used are provided by the samples of fish production, from twenty reservoirs of the referred area, related with the period from 1967 to 1976. Such catches have been distributed into five groups, formed by the combinations of the presence of one to five carnivorous species. ln the course of the analysis, we have observed the action exerted through the irregularity of pluviometric precipitations, the accomplishment of fish stocking, intensity of fishing effort and number of carnivorous occurences, which factors cause great variation in fish productivity. The group of reservoirs with two species of carnivorous fishes revealed itself to be the most productive, reaching the highest values in weight (99.7 kg/ha/year) and in cruzeiros (Cr$ 395,84/ha/year). The lower values of fish productivity, in both cases, have corresponded to the group of reservoirs with only one species of carnivorous fish. Thus, we come to the conclusion that only one species of carnivorous fish is insufficient to maintain the biological balance in greater areas and that the correct combination of two of these species composes the ideal number. We have still verified that the relative participation of non carnivorous species, in the total prodution, is inversely proportional to the number of carnivorous present in each group of reservoirs. Taking into account the main items of the food consumed by the species that occur within the studied reservoirs, we were able to classify them into the following categories: herbivorous – Congo tilapia; planktophagous Nile tilapia; mudfeeders – beiru and common curimatã; insectivorous – sardine; onivorous – apaiari, shrimps, cangati, common piau; primary carnivorous – pescadas, traíra and tucunarés; secondary carnivorous – piranhas and pirarucu. During the period under study the primary carnivorous have predominated in all groups of reservoirs, presenting the greater average values of relative frequency, while the herbivorous and planktophagous have reach the lowest values.
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