Community structure and abundance of bottlenose dolphins Tursiops truncatus in coastal waters of the northeast Gulf of Mexico

Abstract

We examined bottlenose dolphin Tursiops truncatus community structure and abundance in the northeast Gulf of Mexico coastal waters stretching from St. Vincent Sound to Alligator Harbor, Florida, USA. Photographic-identification surveys were conducted between May 2004 and October 2006 to gain an understanding of dolphin distribution in this region. Dolphins were distributed year-round throughout the region; however, individual sighting records indicate that 2 parapatric dolphin communities exist. We conducted mark-recapture surveys using photographic- identification techniques to estimate the abundance of dolphins inhabiting the 2 areas these communities reside in: St. Vincent Sound/Apalachicola Bay, western; and St. George Sound/ Alligator Harbor, eastern. Sighting records of individual dolphins from 2004 to 2008 support the existence of 2 communities in these areas; only 3.5% of distinctive dolphins photographed were seen in both western and eastern areas. The 2 communities differ in their structure: the eastern area supports a more transient population with 45.7% of distinctive dolphins photo graphed only once compared with 28.3% in the west. Independent estimates of abundance (N, 95% CI = [low, high]) were calculated using the Chapman modification of the Lincoln-Petersen method for June 2007 and for January and February 2008 for the eastern area (242 [141-343], 395 [273-516]) and for the western survey area (197 [130-264], 111 [71-150]), respectively. Our results serve as a baseline that can be used by the US National Marine Fisheries Service to manage bottlenose dolphins in this region. © Inter-Research 2011.