Effects of Reservoir Drawdown on Available Habitat: Implications for a Tropical Largemouth Bass Population

In temperate reservoirs, habitat quality and availability can be vital to year-class formation of young largemouth bass. We assessed littoral habitat availability for largemouth bass in a tropical reservoir. Habitat characteristics (slope, substratum, and cover) were measured at 5 water levels (169, 170, 171, 172, and 173 m above mean sea level) at 15 30-m sites in Lucchetti Reservoir. Total structural habitat availability declined sharply at lower water levels, and both inundated terrestrial vegetation and woody debris were absent at the lowest water level examined. Coarse substrates (gravel, cobble, and boulder) were more common at higher water levels, and fine substrates (primarily clay) dominated at lower water levels. Annual catch rates of age-1 largemouth bass from 1993-2000 were significantly related to estimated mean structural habitat availability for the previous spawning season. Water level appears to affect largemouth bass population size partly through availability of habitat, presenting an opportunity for population management through habitat manipulations. Potential water level management protocols are discussed.

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