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Description
Boat-based photo-identification surveys of Pacific coast bottlenose dolphins (Tursiops truncatus) were conducted from 1981 to 2001 in six study areas along the California and Northern Baja coastline: (1) Ensenada, Baja California, Mexico; (2) San Diego, California; (3) Orange County, California; (4) Santa Monica Bay, California; (5) Santa Barbara, California; and (6) Monterey Bay, California. Sighting histories and photographs from all six areas were integrated into one comprehensive catalog, consisting of 697 individuals, to analyze bottlenose dolphin movement patterns along the Pacific coast. Two hundred forty-five individuals identified in Santa Monica Bay from 1997 to 2001 were compared to the existing Cetacean Behavior Laboratory (CBL) catalog, containing 626 individuals identified in the other five study areas from 1981 to 2000. The majority of Santa Monica Bay dolphins (71%, n = 175) were matched to the CBL catalog, and were seen in all study areas, indicating that they belonged to the same population. Some analyses were carried out using both the entire CBL catalog and a subset of 397 CBL dolphins only sighted from 1996 to 2000, as some CBL dolphins seen only from 1981 to 1989 were possibly no longer in the population. The percentage of CBL dolphins seen in Santa Monica Bay greatly increased from 28.0% to 43.3% when using only the 1996-2000 data subset. Three hundred sixty-three of all identified individuals (52.1%) were seen in two or more study areas, of which 263 individuals (72.5%) displayed longshore movement reversals, with a maximum documented number of ten movement reversals. Minimum travel distances ranged from 59 to 965 km, with three individuals ranging over the entire study area from Ensenada to Monterey. The most rapid documented travel speed was 94.5 km/day for one dolphin observed traveling 189 km from San Diego to Santa Monica Bay in two days. Sighting frequencies ranged from one to 40 (mean = 6.98, SD = 7.16), with individuals sighted over a range of one to 20 years (mean = 11.65, SD = 5.22) in up to five study areas, indicating little site fidelity to any one region. These results reinforce the hypothesis that bottlenose dolphins are highly mobile and travel rapidly and extensively along the California and Northern Baja coastline in search of optimal feeding opportunities. The open, unprotected, and highly dynamic habitat structure characteristic of the Pacific coastline may account for differences between movement and residency patterns observed between Pacific coast bottlenose dolphins and populations in more sheltered habitats (e.g. Sarasota Bay, Florida). However, other factors such as food resource availability, water temperature, and intraspecies variability also likely play important roles in influencing ranging behavior.
