Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

High fisheries production within estuaries is associated with coastal upwelling, tidal mixing, and land-based runoff including river inflows that vary from climate and human activities. Understanding how estuarine nekton respond to changing river flows remains critical to manage these systems to maintain fisheries production. To compare effects of different river inflows on nekton, we quantified nekton assemblages in marsh edge and open water sites within an active and inactive delta system. Crustaceans dominated assemblages with Palaemonid shrimp contributing 44% to 65% of total catch, differing only by season, and not delta; summer and fall generally supporting higher densities. In contrast, fish density and assemblages differed seasonally between deltas with the largest differences occurring during extended and high spring river discharge into the active delta. During this period, the active delta experienced lowered salinity, temperature, submerged aquatic vegetation (SAV) biomass, and reduced fish densities and richness compared to the inactive delta. Active delta sites supported greater biomass of Callinectes sapidus during the fall at marsh edge sites compared to other season and delta combinations. Nekton densities and habitat use patterns across deltas and seasons reflect a combination of life history characteristics of dominant species and habitat conditions. The high spring river discharge in 2019 impacted habitat availability (reduced SAV biomass), habitat quality (decreased temperatures and salinity), and potentially displaced nekton to un-sampled habitat areas (i.e., interior marsh surface) within the active delta. Understanding how altered inflow impacts environmental and habitat variables supporting estuarine nekton production remains critical to support management.