Gulf Sturgeon (Acipenser oxyrinchus desotoi) in the Mobile Bay Estuary, Alabama: Documentation of Use Outside of Designated Critical Habitat

Greenheck, E.M.; Andres, M.J.; Fox, D.A.; Kiene, D.; Kreiser, B.R.; Nelson, T.R.; Peterson, M.S.; Powers, S.P.; Rider, S.J., and Slack, W.T., 2023. Gulf Sturgeon (Acipenser oxyrinchus desotoi) in the Mobile Bay Estuary, Alabama: Documentation of use outside of designated critical habitat. Journal of Coastal Research, 39(6), 1021–1043. Charlotte (North Carolina), ISSN 0749-0208. Gulf Sturgeon (GS) are an anadromous, federally threatened subspecies of Atlantic Sturgeon that feed primarily in estuarine and marine systems in the northern Gulf of Mexico from October to April. All extant natal river systems and adjacent estuarine and marine environments were designated as critical habitat for GS in 2003, excluding the Mobile River Watershed because of lack of data indicating an extant spawning population at the time of listing. Previous studies had identified that GS from river systems east of Mobile Bay use habitats within the Mississippi Sound, suggesting GS must at least traverse Alabama waters. Therefore, this study's objective was to quantify the use of the Mobile Bay Estuary by GS. GS were acoustically tagged in all extant natal river systems and detected by an array of receivers deployed in the Mobile Bay Estuary during 2016–21. A total of 210 adult and subadult GS from western (n = 97) and eastern (n = 113) river systems were detected in the Mobile Bay Estuary for up to 4 months, with 110 individuals detected from 2 to 6 years during the monitoring period. The sustained use of the Mobile Bay Estuary by GS from western and eastern river systems strongly indicates that Alabama's waters are suitable habitat despite extirpation of the natal spawning population in the Mobile River Estuary. Foraging in the Mobile Bay Estuary is probable because previous sediment and benthic macroinvertebrate sampling in this system indicated relatively low-percent sand content and high polychaete richness, which are characteristic of foraging habitats previously identified in the Pascagoula River delta. The Mobile Bay Estuary is not designated as critical habitat for GS; however, this study indicates nonanomalous use of this habitat by GS during the foraging period, so inclusion of this system under the critical habitat designation should be considered.