Occurrence, Distribution and Reproductive Status of Female Bottlenose Dolphins (Tursiops truncatus) in Roanoke Sound, NC

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I examined the spatial distribution of bottlenose dolphin (Tursiops truncatus) nursery groups in Roanoke Sound, NC, to gain insight into how environmental parameters affect site fidelity, and to determine whether habitat use patterns change based on the reproductive state of females. For mature females, I compiled information on interbirth intervals and length of calf dependency to obtain a more comprehensive picture of the ecology and life history of this age-sex class of estuarine dolphins. I analyzed photo-identification data from Roanoke Sound to compare the location and extent of kernel density estimates of home ranges for nursery groups, non-nursery groups and individual females. Many nursery groups are observed in this area during spring and summer, leading to the hypothesis that Roanoke Sound is an important nursery habitat. The importance of this area to lactating females may be attributable to its relatively shallow depth and abundant seagrass beds, which provide protection and a relatively plentiful supply of prey. In Roanoke Sound, nursery groups (n = 170) were significantly (p < 0.00001) larger than non-nursery groups (n = 68) with a mean of 12 individuals per sighting, while non-nursery groups averaged 4 individuals. Nursery groups and non-nursery groups had a high overlap percentage between ranging patterns, with home ranges overlapping 88%. This demonstrates that there is no specific “nursery area” within the Roanoke Sound, but coupled with the high numbers of large nursery groups sighted during the summer, the entire site itself may be of importance to these females. Four focal females had a mean interbirth interval of 7.5 years, and a mean length of calf dependency of 4.75 years. The females exhibited individual variation in ranging patterns, with habitat use overlap between nursery and non-nursery areas ranging from 11-79%. These females may be choosing areas based on their needs (and those of their calves), either for energetic purposes or protection. Documentation of nursery habitat can aid protection of these important areas through implementation of measures such as safe boating zones and increased water quality monitoring, as well as assist in the development of educational materials.





Reibel, Waverly (2020). Occurrence, Distribution and Reproductive Status of Female Bottlenose Dolphins (Tursiops truncatus) in Roanoke Sound, NC. Master's project, Duke University. Retrieved from https://hdl.handle.net/10161/20479.

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