By-catch of the shrimp trawlnet fishery on the coastal zone of Fortaleza county, Ceará State, Brazil

Abstract

The trawl shrimp fishery on the coastal zone of Fortaleza county, Ceará State, Brazil is a year-round small-scale fishing activity that has been going on since 1983. This study was designed to study its by-catch by means of a sampling system carried out in 44 commercial trips amounting to 488.5 hours of effective fishing on board small-sized trawlers, from July, 1997 to June, 1998. Its main results are summarized as follows; (a) the by-catch was comprised of 97 species belonging to 44 families, among which Sciaenidae (12 species), Haemulidae (10 species), Carangidae (7 species) and Engraulidae (6 species) stand out; (b) the 14 species with higher frequency of occurrence accounted for 90.4% of total catch and the six species with high frequency of occurrence, for 68.6% of total catch; (c) the ratios of the by-catch weight to 1 kg of marketable shrimp were as follows: total weight = 3.28 kg, sorted out as 0.93 kg (28.6%) of potentiallymarketable species (fish and small-sized shrimp) and 2.34 kg (71.4%) of non-marketable fish species; (d) the trend variations of the estimated indices of diversity showed there to be a close monthly interdependence, with thew following mean estimates: species diversity, H’ = 2.610; equitability, E = 0.569; and species richness, D = 8.357; (e) a decreasing trend, with a geometric dependence, was found to exist between number of species in the by-catch and their specific numerical abundance.