Abstract
The aim of the present study was to identify the distribution patterns of migratory fishes in the Jacuí river basin (Rio Grande do Sul, South Brazil), proposing a statistical model of presumed distribution based on geomorphologic environmental data. Through maps of occurrence probability, we hope to contribute to decisions regarding basin environmental management. The analyzed species were: Salminus brasiliensis (dourado), Leporinus obtusidens (piava), Prochilodus lineatus (grumatã) and Pimelodus pintado (pintado). Samples were made through interviews with fishermen and local inhabitants, covering the main channel and tributaries of the rivers Jacuí, Taquari-Antas, Vacacaí, Vacacaí-Mirim, Pardo, Pardinho, Sinos, and Caí. The sampling program resulted in 204 interviews, being 187 considered as valid in 155 different sampling points. The probability of migratory fish occurrence was adjusted through the LOGIT routine of the Idrisi Andes Software: P = e(b0 + b1 . altitude + b2 . basin area) . (1 + e(b0 + b1 . altitude + b2 . basin area))-1, where P is the occurrence probability of the species (0-1) and b0, b1 and b2 are the equation parameters. Model accuracy, for estimating presence, ranged from 82% to 93%. Pimelodus pintado was cited to occur in 121 points among the 155 sampled (78.06%), Prochilodus lineatus in 72 (46.45%), L. obtusidens in 62 (40.00%) and S. brasiliensis in 58 (37.42%). Equation parameters were estimated (± standard error) as follow: S. brasiliensis: b0 = -2.8762 ± 0.2597; b1 = 1.3028 ± 0.0332; b2 = 1.1487 ± 0.0301; L. obtusidens: b0 = -0.8364 ± 0.2213; b1 = -1.5564 ± 0.0462; b2 = 0.9947 ± 0.0206; Prochilodus lineatus: b0= 0; b1= -1.3067 ± 0.0544; b2= 0.8128 ± 0.0177; Pimelodus pintado: b0= -0.9487 ± 0.3688; b1= -0.8269 ± 0.0496; b2= 0.9255 ± 0.0304.
Highlights
More than 15% of the Neotropical fish fauna is composed by migratory species (Carolsfeld et al, 2004), which may need to cover several kilometers to stimulate gonadal maturation (Godoy, 1987)
The present study aims to identify the longitudinal historical distribution pattern of long distance migratory fish in the hydrographic basin of the Jacuí River, which already has an installed hydroelectric production of 1.428,674 MW, and a potential, still not installed one, of 271,004 MW
Pimelodus pintado was present in 121 points among the 155 sampled (78.06%), Prochilodus lineatus in 72 (46.45%), L. obtusidens in 62 (40.00%) and S. brasiliensis
Summary
More than 15% of the Neotropical fish fauna is composed by migratory species (Carolsfeld et al, 2004), which may need to cover several kilometers to stimulate gonadal maturation (Godoy, 1987). Spawning use to happen upstream the adult feeding areas, and stream current carries the eggs and larvae to areas where they will develop In these sites, juveniles will feed and grow until they become big enough to join the main stock (Pitcher & Hart, 1982). Malabarba (1989) presents a list of species of freshwater fish of Patos Lagoon drainage, which includes the Jacuí River. Following Agostinho & Júlio (1999) and Vazzoler et al (1997), the migratory species for Jacuí basin are: Salminus brasiliensis
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