Diversidad Y Abundancia Ictiofaunística Del Río Grande De Térraba, Sur De Costa Rica

Diversidad y abundancia ictiofaunística del río Grande de Térraba, sur de Costa Rica
José Rodrigo Rojas M.1 & Omar Rodríguez S.2
1. 2. Proceso de Planeamiento Ambiental, Centro Nacional de Planificación Eléctrica, Instituto Costarricense de Electricidad, Apdo 10032-1000, San José. Costa Rica; rrojasm@ice.go.cr; yoyi66@yahoo.com, Biólogo Investigador; omarrodriguez@yahoo.com.mx Recibido19-vII-2007. Corregido 02-v-2008. Aceptado 26-v-2008.

Abstract: The diversity, abundance and distributional pattern of freshwater fish communities in the Térraba River, south Costa Rica, were investigated from the early dry season of 2004 to early rain season of 2005. There have been no preview studies on the freshwater fish distribution in Térraba. Therefore, the aims of this study were to determinefish species richness, abundance and distribution there. Fish sampling was done using a combination of gears such as gill net, fine mesh net and visual observation. Thirty three species, 26 genera and 14 families were collected in four sampling sites along the river. The number and biomass captured during the entire study was 984 individuals and 147 410.9 g respectively. Most of them arecarnivorous species (48%), 33.3% are omnivorous and 12% detritivorous, and only two species are herbivorous. The most important species in relative abundance (56.5%) and biomass (53.7%) in the study area was the machaca (Brycon behreae). It should be clear that although the list of fish species that occur in Térraba River is reasonably complete, knowledge of their ichthyogeographic history patterns issuperficial. The main community component was secondary freshwater species; with 17 invading brackish water species and one introduced species (tilapia O. niloticus). Nine species are reported for the first time in this river. The diversity index H` varied from 2.32 (El Brujo) to 1.67 (Coto), a similar pattern was also showed for the other indexes. Most of our results were similar to those of previousstudies on freshwater fish distribution elsewhere, however no significant correlation between species distribution and environmental variables was found, and we hypothesized that the depth and water velocity and geomorphological are major environmental variables that influence the fish distribution. Our findings are opposed to the tendency, for species composition, to increase from upstream to themouth of the river, which is probably due to two major human activities (discharge of waste of pineapple fields and sediments in the main channel). These activities could constitute in the future a real threat for the fish population and other aquatic organisms. Growth rates, competition, predation pressures, community organization, biotic versus physical factors in relation to distribution, andmany other aspects of fish biology remain to be studied. Future surveys will involve more quantitative surveys in different seasons and over time to monitor the long-term variation in the diversity and abundance of freshwater fish species in Térraba. Rev. Biol. Trop. 56 (3): 1429-1447. Epub 2008 September 30. Key words: freshwater fishes, species richness, abundance, spatial and temporaldistribution, River Grande de Térraba, Costa Rica.

Costa Rica, y en especial en la vertiente pacífica, ha experimentado en las últimas décadas un incremento en los estudios sobre los factores ecológicos que determinan la distribución y estructura comunitaria de los peces (Bussing 1974a, b, 1976, Bussing y López 1977, Constantz et al. 1981, Winemiller 1983, Alpírez 1985, Burcham 1988, Winemiller

yMorales 1989, Lyons y Schneider 1990, Wootton y Oemke 1992, Winemiller 1993, Bussing et al. 1994, Rojas et al. 1994, Chicas 2001), no obstante resultan insuficientes si consideramos la velocidad del deterioro e impactos ambientales negativos a los que están expuestas la mayoría de los ríos de esta vertiente (Estado de la Nación 2006). El río Grande de Térraba
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Rev. Biol. Trop. (Int. J....