Bottlenose dolphins were photo-identified in the area between the islands of Maui, Lana‘i, Moloka‘i and Kaho‘olawe, Hawai‘i (an area of approximately 3,000 km2) between November 2000 and March 2001. A total of 328 hours were spent on the water during 49 days, and bottlenose dolphins were encountered on 32 occasions on 22 days. Fifty-nine individual dolphins had long-term recognizable markings (dorsal fin or back notches), and an additional 12 individuals (including 4 calves) were also documented based on body scars, dorsal fin shape or pigmentation patterns; thus, approximately 82% of individuals are thought to be recognizable in the long-term. Identification data were combined with a catalog of 63 individuals that had been documented in the same study area in 1999 and during the spring of 2000. During the entire period each “marked” individual was documented an average of 3.6 times (range 1-16), though individuals were not re-sighted randomly; some were seen more often and some less often than expected by chance. A mark-recapture analysis of the population using identifications from 1999 and from November 2000-March 2001, taking into account the proportion of marked individuals, produced an estimate of 134 dolphins (95% CI = 107-179). Using modeled rates of discovery the population was estimated at 122 individuals. Given the size of the study area and the presumed transitory nature of bottlenose dolphins around oceanic islands, the population in this area is surprisingly small.
Citation:
Baird, R.W., A.M. Gorgone, A.D. Ligon, and S.K. Hooker. 2001. Mark-Recapture Abundance Estimate of Bottlenose Dolphins (Tursiops truncatus) Around Maui Nui and Lana‘i, Hawai‘i, During the Winter of 2000/2001. Report prepared under contract #40JGNF0-00262 to the Southwest Fisheries Science Center, National Marine Fisheries Service, La Jolla, CA.
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