Larval fish abundance in relation to environmental variables in two Texas Gulf Coast rivers

Abstract

Phenology of fish spawning in lotic ecosystems depends on interactions between species life history strategies and patterns of environmental variation related to hydrology and seasonality. To further study these relationships, we examined patterns of larval fish abundance in relation to discharge and other environmental variables in the Brazos and Trinity rivers, Texas. From March 2013 to March 2014, environmental data and larval fishes were collected twice each month using drift nets. Multivariate analyses indicated that, at both study sites, water temperature was the primary mechanism driving temporal and taxonomic variation in larval fish assemblage structure at the family level. However, in the Trinity River, assemblage structure was significantly associated with discharge, albeit to a lesser degree than with water temperature. Cyprinid protolarvae dominated catches in both rivers and did not seem to be constrained by any aspect of the flow regime, as evidenced by their high abundance throughout the reproductive season (April–September). Analysis of larval fish abundance at the family level compromised our ability to infer spawning dynamics of species classified as fluvial specialists. Further research enabling identification of larvae to species-level is needed to elucidate how flow regime components influence reproduction and recruitment of fluvial specialists.