Alternate Title

Summer Movement Patterns of Bottlenose Dolphins in a Texas Bay


Radiotracking of 10 bottlenose dolphins (Tursiops truncatus), from 9 July 1992 to 13 Sep. 1992, was conducted in Matagorda Bay, Texas. The mean range size was 140 km2 (SD = 90.7). Males and females had similar range sizes, though males visited the extremities of their ranges more frequently. Several generalities were observed: (1) dolphins were capable of traversing their range in several hours; (2) dolphins traveled widely on some days, whereas on other days, movement was very confined, within 1-2 km2; (3) dolphins tended to spend about 1-4 d in a particular portion of their range; (4) movement tended to be more confined at night than during daytime; and (5) dolphins tended to visit the extremes of their ranges only in the daytime. Individually, dolphins showed preferences for geographic regions within the bay; ranges overlapped strongly for some dolphins, yet only at range boundaries for others. Photoidentification surveys between May 1992 and June 1993 indicate that some individuals probably reside in Matagorda Bay for one or more years, whereas other individuals do not and can be found in other Texas bays. Limited ranging within the bay system and a lack of movement offshore may indicate that some of the dolphins are susceptible to localized anthropogenic and naturally occurring toxins. Examples of movement between bays, though few in the present data set, indicate that on the Texas coast, within-bay dolphin populations are probably not truly isolated.