Identification and Delineation of Essential Habitat for Elasmobranchs in Estuaries on the Texas Coast

Abstract

Essential habitat is required for a given species to complete its lifecycle and includes habitat for breeding, feeding, and growth. Estuaries provide essential habitat for many fishes, including elasmobranchs, particularly as nurseries. Shore-based, gillnet surveys have documented ten elasmobranch species (sharks and batoids) inhabiting Texas estuaries; however, limitations in the methodology, spatial, and temporal scope employed mean the role of these estuaries as elasmobranch nurseries remains uncertain. Therefore, an alternative sampling technique was implemented to survey open water locations in two Texas estuaries during the peak time of putative elasmobranch nursery usage (May to October). Ten species of elasmobranch were observed, including a shark, Carcharhinus porosus, and batoid species, Hypanus americanus, that were not documented in previous surveys. The most commonly encountered species, Carcharhinus brevipinna, comprised 45% of individuals caught, in contrast to previous surveys of these estuaries, in which the species was less than 1% of the total elasmobranch catch. The results revealed a distinction between sharks and batoids in terms of the life history stages present, as well as the depths and distances from the tidal inlet of areas in which they were encountered. Young-of-the-year and small juvenile Carcharhinus brevipinna and Sphyrna lewini were observed across multiple years and in multiple months within years at one site, suggesting that one of the sampled estuaries functions as a nursery. Although putative nurseries for these species have been identified elsewhere in the world, estuaries serving as nursery grounds in the western Gulf of Mexico are not well described.