Variação sazonal da distribuição, abundância e diversidade dos peixes na zona de arrebentação da Praia do Cassino, RS - Brasil

Abstract

From march, 1980 to february, 1981, regular biweekly beach seine fish samples were taken at eight fixed stations along a 67 km stretch of sand beach just south of the mouth of Lagoa dos Patos, RS, Brazil. A total of 49,170 fishes, belonging to 41 teleost species, were caught by a 9 m beach seine in the marginal surf zone waters less than 1.5 m deep. Eleven species, represented mostly by juveniles, were present in more than 99 % of the catches. The highest (20) and the lowest (6) species diversity were found in the months of february (summer) and July (winter), respectively. four species, Trachinotus marginatus, Mugil liza, Menticirrhus littoralis and Oncopterus darwini were present in the catch year-round. Except for Mugil liza, which was also very abundant in the Lagoa, the others were rarely or have never been caught in the estuary. Seven species were caught in 6 to 11 months of the year, including, Odontesthes bonariensis, Xenomelaniris brasiliensis, Mugil curema, M. hospes Lycengraulis grossidens, Brevoortia pectinata and Micropogonias furnieri, all typical estuarine fishes. Fishes caught on the beach up to 5 months of the year were Anchoa marinii, Sardinella brasiliensis, Caranx latus, Ramnogaster arcuata and Jenynsia lineata. Among them, only A. marinii showed a peak of high abundance in summer, and the combined catches of the remaining species did not reach to 1 % of total yearly catch. Furthermore, 25 species were caught '' incidentally" mostly during the warmer months of the year. They included juveniles of coastal marine and estuarine fishes, usually found in slightly deeper waters of the area, and tropical fishes from the north. Few characids were also caught on the beach, which were probably washed out from the lagoa ar small coastal creeks. An excepcionally large catch on the 24th of february, 1981, was estimated to have 51,851 individuals of Mugil hospes. Data of this catch were treated separetely and were not included in the general analysis of the fish comunity. The surf zone of the study area is apparentely proviging a fish community assemblage different from the adjacent estuary of lagoa dos Patos and coast waters over 5 meters of depth. lt is an important nursery ground and possibly also a transient zone for many species in southern Brazil. Preliminary observations on the commercial haul seine catches have been included in the discussion of life histories and movements for the most abundant species.