Effects of three different water-control structures on the movements and standing stocks of coastal fishes and macrocrustaceans

Water-control structures are used in the coastal zone to enhance species-specific habitat, mainly for waterfowl, and in attempts to control saltwater intrusion and soil erosion. These structures invariably affect the movement of marine transient organisms. We used traps and trawls to evaluate the effects on nekton of a low-elevation weir, a fixed-crest weir, and a slotted weir. Data were collected from 15 February through 30 July in 1983, 1984, and 1986. Species richness and emigration of most species decreased as water control increased. Average weight per emigrating brown shrimp Penaeus aztecus increased with water control, although total biomass decreased. Immigration and emigration of brown shrimp were delayed by water control, and this effect was increased in ponds having greater water control. The number of emigrating brown shrimp was 3.4 times greater (1.8 times greater for biomass) from a pond controlled by a slotted weir than from one controlled by a fixed-crest weir.