Nekton densities in shallow estuarine habitats of Texas and Louisiana and the identification of essential fish habitat

The Magnuson-Stevens Fishery Conservation and Management Act (Magnuson-Stev ens Act) of 1996 requires the identification of essential fish habitat (EFH ) for fishery species under federal fishery management plans (FMPs). As def ined in the Magnuson-Stevens Act, EFH includes waters and substrate necessa ry for spawning, breeding, feeding, or growth to maturity. Without EFH, fis hery species will be unable to maintain the productivity needed to support a sustainable fishery or contribute ecologically to aquatic ecosystems. The highly productive estuaries in the northern Gulf of Mexico contain many ha bitat types that are potentially essential for species under FMPs such as b rown shrimp Penaeus aztecus, white shrimp P. setiferus, pink shrimp P. duor arum, gulf stone crab Menippe adina, red drum Sciaenops ocellatus, gray sna pper Lutjanus griseus, and bluefish Pomatomus saliatrix; these species spen d their juvenile life stages in estuarine nurseries. Estuarine habitats als o may be important for prey required as forage by managed species and for o ther fishery species not under FMPs. My objective in this paper was to summ arize information on densities of juvenile fishery species and other animal s (all generally <100 mm total length) in shallow-water estuarine areas of Texas and Louisiana. I attempted to identify where these species live (deli neate their habitat) and to analyze density patterns within habitats that w ould be useful in distinguishing EFH. My analysis was restricted to data co llected with enclosure sampling techniques because these techniques have be en shown to provide comparable density estimates among highly diverse shall ow-water areas. Habitat types evaluated included Spartina alterniflora mars h edge (SAME), mixed-vegetation marsh edge, inner marsh (>5 m from open wat er), submerged aquatic vegetation (SAV), oyster reefs, and shallow nonveget ated bottom (SNB). Data also were categorized by season, salinity regime, e stuarine system, and year of collection. Mean densities among habitat types frequently varied in relation to salinity regime, but overall, SAME was us ed most by brown shrimp, white shrimp, blue crab Callinectes sapidus, spott ed seatrout Cynoscion nebulosus, and southern flounder Paralichthys lethost igma. Highest densities of pink shrimp, red drum, and sand seatrout Cynosci on arenarius were found in SAV. Stone crabs had highest mean densities on o yster reefs and gulf menhaden Brevoortia patronus on SNB. Each of the six h abitat types examined ranked first or second in use by at least one of thes e fishery species. Thus, all of these habitat types are likely essential fo r some fishery species. The analysis highlighted many of the challenges con fronted in determining habitat-use patterns and emphasized the need for add itional systematic sampling to examine geographic variability in habitat us e and to examine distribution patterns within habitats. However, in additio n to analyses of intrahabitat densities, the identification of EFH requires information on functional relationships between fishery species and habita t characteristics.