Use of fragmented reservoir habitats by larval fish assemblages across years with contrasting hydrological conditions

Abstract

Sedimentation in aging reservoirs generally reduces fish habitat quality and quantity, often isolating coves and pools from the main body of the reservoir. In some cases, however, habitat fragments created by sediment deposition in the river-reservoir interface zone support high fish diversity, and they could potentially replicate features of nursery habitats in natural river floodplains if they are regularly connected to the greater river-reservoir. We examined the structure of larval fish assemblages in fragmented coves and pools within the transitional zone of an aging reservoir (Lake Texoma) over 2 years with contrasting hydrological conditions (dry year with low connectivity versus wet year with high connectivity to the main body of the reservoir). We found that larval assemblage structure varied spatially across the two river arms of the reservoir and temporally across the dry and wet year. In both years, assemblages were dominated by Dorosoma species and Menidia beryllina, taxa considered habitat generalists. The abundance of other taxa, particularly Lepomis, Pomoxis, and Morone species, increased with greater habitat connectivity in the wet year. Many taxa considered dependent upon riverine or floodplain habitats were collected during the wet year at sites where they had not been collected in the dry, low-connectivity year. Our results suggest that these fragmented habitats can provide nursery habitats for a variety of fish taxa, but that the structure of larval assemblages using them varies widely based on hydrological connectivity.