Determining If 'Orientation Against the Current' Is a Dolphin Foraging Tactic

Common bottlenose dolphins (Tursiops truncatus) off Port Aransas, Texas, have been observed engaging in an unusual behavior termed “orienting against the current” (OAC). OAC, last described in 1990, consists of dolphins swimming in the opposite direction of the current, remaining relatively stationary in spatial positioning. To test the hypothesis that OAC is a foraging tactic, environmental conditions were assessed when dolphins engaged in OAC compared to traditional foraging off Port Aransas. Data were collected using a survey’s theodolite positioned at the convergence of the Corpus Christi Ship Channel, Lydia Ann Channel, and Aransas Channel. Dolphins were tracked from June 2021 to October 2022. Season, time of day, current speed, group size, and OAC occurrence were recorded. OAC occurred most frequently between fall (September – December) and spring (March – June) with the highest peak during winter, in the morning (7am – 11 am) and evening (5:01pm – 8pm), in fast current speeds (2.01 – 3 knots), and in large group sizes (11+ individuals). Previous studies found that dolphin foraging off Port Aransas was most prevalent during fall to spring, in the morning and evening, in fast current speeds, and in small group sizes, both supporting and contradicting the OAC foraging tactic hypothesis. Video footage of dolphins engaged in OAC showed behaviors typical of foraging such as tossing fish, tight circling, and high arching dives as well as dolphins actively catching fish. Identification of environmental conditions when OAC occurs most prevalently may aid efforts to find dolphins engaged in this foraging tactic at other locations and augment understandings of the dynamics of dolphins within their ecosystems.