Abundance and Occurrence of Common Bottlenose Dolphins (Tursiops truncatus) in Three Estuaries of the Northwestern Gulf of Mexico Gulf and Caribbean Research

Current abundance estimates for populations of common bottlenose dolphins (Tursiops truncatus, Montagu, 1821) in bays, sounds, and estuaries are lacking throughout most of the northwestern Gulf of Mexico, including areas of Texas and western Louisiana. To address this issue, we conducted 92 small-boat photographic identification surveys covering ~2000 km2 and comprising ~11,000 km of track-line in winter and summer seasons in West Bay, TX (2014 – 2015, n = 25), the Galveston Bay, TX system (2016, n = 50), Sabine Lake, TX (2017, n = 17), and adjacent coastal waters. Individual dolphin encounter histories were constrained by spatiotemporal parameters to approximately represent 1) a “Bay” estimate of individuals limited to the interior of each embayment, and 2) a “Selective” estimate of the number of individuals in each survey area (including nearshore coastal waters), filtered for potential transient dolphins. Using the Selective dataset, estimated dolphins (95% CI) were (winter and summer, respectively) 38 (29 – 47) and 37 (33 – 40) for West Bay, 842 (694 – 990) and 1132 (846 – 1417) for Galveston Bay, and 122 (73 – 170) and 162 (114 – 210) for Sabine Lake. A range of 4-15% of marked individuals in each study area were identified as inter-bay matches. These results provide new insights on the potential spatial range of each population, update previous abundance estimates for West Bay and Galveston Bay, and contribute novel population information for Sabine Lake and adjacent coastal waters of the northwestern Gulf of Mexico.