Abundance of Bottlenose Dolphins in the Bays, Sounds, and Estuaries of North Carolina

Abstract

We conducted a mark‐recapture survey of bottlenose dolphins Tursiops truncatus in the bays, sounds, and estuaries of North Carolina during July 2000, using photographic identification techniques. During this survey we took 7,682 photographs of dolphins and, of these, 3,457 images were of sufficient quality for analysis. We identified 306 dolphins from distinctive nicks and notches on their dorsal fins. Eighry‐six dolphins were photographed on more than one occasion during the course of the survey; one dolphin was photographed on four separate days. We then applied the results of our photographic analyses to several mark‐recapture models and examined potential violations of the assumptions of these models, including an unexpected correlation between photo quality and mark distinctiveness. Our analysis suggests that our results are robusr to possible violations of these assumptions. The resulting estimates were then scaled to account for the proportion (0.46) of unmarked dolphins in the population. Our best estimate of the number of dolphins present in the inshore waters of North Carolina during July 2000 is 1,033 with a 95% Confidence Interval of 860–1,266 (CV = 0.099). Most dolphins were found in the northern part of the study area, which includes the second largest estuarine system in the United States.

Survival, density, and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill

“…Correct identification of fins is critical to unbiased estimation of demographic parameters (Würsig & Jefferson 1990, Friday et al 2000, Read et al 2003. To help avoid false matches among photos, we graded the quality of images as Q-1 (excellent), Q-2 (average), or Q-3 (low) using a weighted scale based on 5 characteristics: focus, contrast, angle, fin visibility/obscurity, and proportion of the frame filled by the fin (Urian et al 2014).…”

“…The natural markings, principally nicks and notches along the trailing edge of common bottlenose dolphin Tursiops truncatus dorsal fins, as well as body scars and pigmentation patterns, can persist throughout their lifetime (Lockyer & Morris 1990, Würsig & Jefferson 1990, Read et al 2003. Capturerecapture analyses are commonly applied to photo-ID data to estimate abundance (Wilson et al 1999, Read et al 2003, Balmer et al 2008) and survivorship (Speakman et al 2010). …”

Abundance, survival and temporary emigration of bottlenose dolphins (Tursiops sp.) off Useless Loop in the western gulf of Shark Bay, Western Australia

“…The degree of distinctiveness varies among dorsal fins of individuals and some are not sufficiently marked to be included in capture-recapture analyses, which only pertain to the distinctly marked population (Wilson et al 1999;Read et al 2003). Each individual in the catalogue was therefore given a distinctiveness score, based on the amount of information contained on the leading and trailing edges of the dorsal fin.…”

“…The photo-identification method is widely applied with capture-recapture methods to estimate abundance and other demographic parameters, such as survival and temporary emigration rates, of small cetaceans (e.g. Wilson et al 1999;Read et al 2003;Parra et al 2006;Silva et al 2009). The main advantage of using photo-identification data for capture-recapture analyses is that animals do not need to be physically captured to be marked (Hammond 1986(Hammond , 1990.…”

First estimate of common bottlenose dolphin (Tursiops truncatus) (Cetacea, Delphinidae) abundance off Uruguayan Atlantic coast

“…Populations inhabiting open habitat, however, are potentially larger (generally between 200-1000 individuals) and exhibit a lower degree of residency (e.g. Bearzi et al, 1997;Defran and Weller, 1999;Read et al, 2003). In the Southwest Atlantic Ocean (SWAO) there are records of bottlenose dolphins from Amapá State (04°33'N, 37°00'W), northern Brazil to the province of Tierra del Fuego (54°55'S, 67°30'W), southern Argentina (e.g.…”