Winter stock structure of bottlenose dolphins in North Carolina

The objective of this study is to determine the stock identity of bottlenose dolphins present off the North Carolina coast in the winter months, the degree of mixing among these stocks, and the patterns of association of dolphins from particular stocks. We are interested in testing the following two hypotheses: (1) that only the migratory and northern NC stocks overlap during winter and that the migratory stock does not move into the range of the southern NC stock; and (2) dolphins preferentially associate with individuals from their own stock during the period of mixing. To test these hypotheses, we conducted simultaneous photo-identification surveys at three sites (Hatteras, Beaufort, and Wilmington ) during winter months, November to April, as defined by the current NMFS management regime.

We conducted a total of 30 simultaneous surveys and met our goal of completing 10 simultaneous survey days between the months of November 2004-April 2006, despite the challenges of conducting coastal surveys in the winter months! For each survey, we attempted to survey both the waters close to shore (less than 1 km from the beach) and, weather permitting, out to the 6 km stock boundary defined by NMFS. At each encounter with dolphins we attempted to take dorsal fin images of each dolphin using digital Nikon cameras with 300-mm lenses. We encountered large groups of dolphins, with group sizes ranging up to 400 dolphins, and obtained 9,764 images.

We are in the process of collating, editing and processing the nearly 10,000 dorsal fin images that were taken during our surveys. We are evaluating each image for quality and dorsal fin distinctiveness, and once evaluation of the images is complete, we will begin the time-intensive process of matching the dorsal fin images that meet our criteria to our photo-ID catalog, and to the Mid-Atlantic Bottlenose Dolphin Photo-ID Catalog (MABDC).

Supported by the North Carolina Sea Grant Fishery Resource Grant Program

For additional information contact: Kim Urian (kurian@ec.rr.com)