Variation in Fish Assemblages Among Three Submerged Aquatic Vegetation (SAV) Habitats and Non-Vegetated, Mudflat Habitat on the Atchafalaya Delta, Louisiana

The active Atchafalaya River delta in coastal Louisiana is a dynamic tidal freshwater wetland with a diverse mix of freshwater and estuarine fish species.  Adjacent to the emergent wetland islands on the delta are large expanses of submerged mudflats, some of which are covered with submerged aquatic vegetation (SAV).  We sampled the three dominant SAV habitats and non-vegetated mudflats for fish and invertebrates, quarterly, using two sampling gears, a 1-m² aluminum throw box and a push-barge electrofishing system.  The use of these 2 different methods allowed us to catch a wider range of fish species and sizes than if we had only used one gear.  The three dominant SAV habitats sampled were: 1) Vallisneria americana (VALAMR) typically found on deep open flats; 2) Potamogeton nodosus (POTNOD) found along higher elevation flats near channels, and 3) a Myriophyllum spicatum dominant mixed SAV habitat (MSMIX), found in shallow protected interior flats. This MSMIX habitat is variable in species composition, but is usually dominated by M. spicatum and may include several other SAV species including Najas guadalupensis , Zannichellia palustris, Potamogeton pusillus , Heteranthera dubia, Ceratophyllum demersum, and Potamogeton crispus. SAV species composition and dry biomass were determined for each of the throw box samples.  Fish species composition and abundance, among habitats and seasons, were analyzed with CLUSTER, ANOSIM, and SIMPER procedures using Primer v6 software.

                Analysis of the first year of data has yielded some interesting results, but a second year of sampling data will be analyzed and included in the results for this poster.   Although there are differences in sampling efficacy between the two sampling gears, there were obvious differences among habitats within gears, and many of these differences were consistent for both sample gears.  Total numbers of fish and total organisms were consistently highest in the MSMIX habitat, followed by VALAMR and POTNOD, with the non-vegetated mudflat habitat having the lowest catches overall.  Brevoortia patronus, Mugil cephalus, Lucania parva, and Cyprinodon variegatus were always most abundant in the MSMIX habitat and the livebearers (Gambusia affinis, Poecilia latipinnia, Heterandria formosa) and sunfishes (Lepomis macrochirus, Lepomis microlophus, and Micropterus salmoides) were only collected in the MSMIX habitat.  In contrast, Macrobrachium ohione, Palaemonetes spp., and Fundulus grandis catches were always highest in the VALAMR habitat.  Analysis of similarity tests indicated these differences among habitats were statistically significant for both the electroshock data (p=0.003) and the throw box data (p= 0.001).