Occurrence and Behavior of Hawaiian Spinner Dolphins (Stenella longirostris) Along Oahu’s Leeward and South Shores

Abstract: The spinner dolphin (Stenella longirostris) is a delphinid that occurs in both pelagic and coastal tropical and subtropical habitats worldwide. A model of the behavior and ecology of this species was described for a resident population along the Kona coast of the island of Hawaii by Norris et al. (1994). To assess the applicability and variability of this model in divergent coastal habitats, the occurrence and behavior of spinner dolphins resident along the southern and western shores of the island of Oahu, Hawaii, was studied over a five-year period. The findings reveal that spinner dolphins off Oahu carry out their daily cycle in a manner similar to those off Kona, but that some noteworthy differences exist in the manner in which dolphins off Oahu use the nearshore habitat. Spinner dolphins exhibited strong preferences for specific locations along the west coast of Oahu, but not along the southern shore, where the average pod size was consistently larger. Resting and social behaviors were tied primarily to the time of day, rather than to any specific site along the coast. Spinner dolphins consistently exhibited a strong affinity for the 10-fathom isobath, indicating that shallow waters are likely the primary coastal feature promoting daytime residence. Foraging was initiated typically in the late afternoon along the edges of banks where vertically and horizontally migrating mesopelagic prey presumably first ascend to shallower depths. Spinner dolphins on Oahu use the coast opportunistically and, therefore, over time, could respond to recent increases in human encroachment by shifting the location and/or timing of their occurrence and behavioral activities.

Key Words: Spinner dolphin, Oahu, behavior, resting, foraging, activity index, Stenella longirostris

Document Type: Research article

DOI: 10.1578/AM.30.2.2004.237

Page Numbers: 237-250

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