Behavior Patterns of Bottlenose Dolphins in San Luis Pass, Texas

Common bottlenose dolphins (Tursiops truncatus) are behaviorally flexible cetaceans that have adapted to a wide variety of habitats. In the San Luis Pass area near Galveston, Texas, there are two populations of bottlenose dolphins, distinguished through long-term photo-identification studies, which use adjacent habitat in different ways. A small resident population makes use of the shallow bay system, while the larger, more transient population remains outside the bay along the Gulf of Mexico coastline. A 13-mo study was conducted to examine the behavior of these populations and to explore the hypothesis that although they overlap geographically, each population utilizes the area differently. The behavior of focal groups was assessed by instantaneous sampling, and a time budget of each behavior per unit effort was calculated. When these populations mix in Gulf of Mexico waters, social activity and travel were the primary behaviors observed. Resident dolphins foraged predominantly in the bays and pass, and displayed group foraging behavior. In contrast, Gulf dolphins were only observed foraging in coastal waters, and did so individually. These behavioral differences may reflect strategies based on habitat variation, but may also be indicative of distinct social structures between resident and Gulf populations. There was a seasonal component to behavior and group size, with larger mixed groups and more social behavior occurring in summer. Finally, resident dolphin behavior varied by time of day, with a peak in foraging in the morning and socializing in the afternoon. The results of this study suggest that these adjacent groups are distinct populations that have partitioned their habitat into separate niches, and thus should be treated separately in management decisions