Bottlenose dolphin responses to pingers

Abstract

I observed bottlenose dolphins (Tursiops truncatus) from a shore-based, rooftop theodolite station on the southeast side of Galveston Island to test their behavioral response to pingers. Pingers have been shown to alert some cetacean species to the presence of nets, but have not been tested adequately for bottlenose dolphins. Data were collected from September 1997 to August 1999 for behavioral variables (behavior, cohesion level, and group size) as well as for track variables (linearity, track speed, and reorientation) to determine differences between three levels of an experimental factor: active, dummy, and control. An active treatment consisted of pingers that contained batteries and were pinging, while a dummy treatment consisted of pingers that did not contain the batteries and would not ping, and the control with no pinger. Hypotheses were that with a change of pinger treatment, dolphins would not exhibit different: 1) behaviors, 2) cohesion levels, 3) group sizes; and 4) movement patterns. In addition, two criteria were used to select case-study tracks that exhibited possible reactions by the dolphins to pingers: 1) All tracks of dolphins that extended "through" the treatment line or just next to either buoy, as if there was nothing to deter dolphin movement; and 2) All tracks that showed an approximate 180-degree turn by dolphins upon nearing or reaching the treatment line, as if movement was deterred. The first criterion was expected to occur for dolphin groups during control or dummy days, while criterion 2 was expected to occur for dolphin groups during active treatment. Chi-square tests and MANCOVA's did not detect significant differences among treatments; however, case studies showed interesting trends. Four of 5 dolphin pods that turned 180 degrees occurred on days when the treatment was active. At no time did a dolphin or dolphin pod swim through the treatment line during an "active" treatment. However, during "dummy" or "control" treatment days, 9 dolphins or dolphin groups, of 14 case study dolphin groups swam through the treatment line. It is apparent that the "active" pinger may have been deterring dolphins from passing across the treatment line.