The construction of dams and reservoirs has led to dramatic alterations to the hydrology of rivers. Amongst the many potential impacts these altered flow regimes have had upon riverine fishes are changes in the availability and accessibility of floodplain habitats. Many species of riverine fishes use these off-channel floodplain habitats during the larval and juvenile phases of their life histories. While most of these species are capable of completing their life history within the confines of the main river channel, there seems to be negative consequences in growth, survival, and population levels associated with changes in the availability, access to, and quality of floodplain habitats due to altered flow regimes. The decline of widespread species such as alligator gar Atractosteus spatula blue sucker Cycleptus elongatus has been attributed, at least in part, to the loss of these habitats throughout their range. Furthermore, critical nursery habitats for many other threatened and imperiled riverine fishes have not been identified. It is likely that many may be dependent upon floodplain habitats to some extent.
Given the severity of the current drought, changing precipitation patterns, and increasing water demands, there is likely little that can be done in Texas to address altered flow regimes in large rivers to increase the connectivity between main channel and floodplain habitats. However, recent research by Texas Parks and Wildlife suggests that the river-reservoir interface (RRI) represents an ecotone between two distinct habitat types and as such, may play an important role in maintaining species richness and diversity in these heavily modified systems. In particular, the high levels of sedimentation associated with the drop in current velocity during the transition from lotic to lentic conditions can create off-channel habitats that are at least superficially similar in hydrology and ecology to the floodplain habitats used as nursery habitats by many riverine fishes. The presence of these off-channel RRI habitats may be critical for the long-term persistence of fishes that require floodplain habitats to successfully reproduce, but are otherwise capable of maintaining populations in the modified conditions of a river-reservoir system. However, there has been no attempt to determine whether these off-channel habitats in the RRI function as surrogate floodplain habitats for riverine fishes and how factors such as their physicochemical characteristics and lateral connectivity might affect their productivity as nursery habitats.
The objective of the proposed study is to assess the use by larval and juvenile fishes of off-channel habitats in the RRI between the Trinity River and Lake Livingston, and to compare these fish assemblages with those using similar natural floodplain habitats in the middle Trinity River.