Spinner dolphin background information
Spinner dolphins (Stenella longirostris) derive their name from their often acrobatic leaps from the water in which they rotate about their longitudinal axis (i.e., spin) or sometimes somersault in mid-air. The function of these spins and leaps is still not understood but in certain contexts may signal others.
Spinner dolphins can be found in tropical and temperate waters worldwide (Perrin & Gilpatrick, 1994). Spinner dolphins are abundant throughout the waters of the Hawaiian Islands including the Northwestern Hawaiian Islands (Shallenberger, 1981; Norris and Dohl, 1980; Norris et al., 1994; Mobley et al. 2000; Lammers, 2004). Although extensive movements within island regions by individuals have been documented (see Lammers, 2004), Caretta et al. (2004) indicate that to date it is not known if spinner dolphins regularly travel interisland or whether distinct populations exist. The Hawaiian stock of spinner dolphins appears to be distinct from the stock of the ETP (Perrin, 1975; Dizon et al., 1994). The most intensively population of spinner dolphins resides in waters at or near Kealikekua Bay of the Big Island. Based on intensive photo-identification efforts by Norris et al. (1994) and more recently by Ostman (1994), Ostman estimated a population of 2,334 spinner dolphins respectively along the Kona coast alone. Given this number, it is likely that the population of spinners across all the Hawaiian Islands is likely more toward the upper boundary of the 95% confidence interval of 6,415 provided by Mobley et al. (2000).
The Leeward coast of Oahu is best known for its spinner dolphins that come into three main bays and sandy bottom shallow areas in the morning hours for resting and socializing. Along the Waianae coast of Oahu in early morning hours, spinner dolphins (Stenella longirostris) gather in shallow inshore waters (< 17 fathoms deep, median depth = 11 m) in Makua Bay, Pokai Bay, and Kahe Point after foraging at night in deeper waters (Lammers, 2004). These areas are used by the dolphins for resting, nursing, and social interactions. Dolphins are often observed milling in these areas in groups ranging from two to a hundred or more individuals. Often, large groups contain smaller sub-groups of individuals that vary unequally in sex and age-class (calves versus non-calves). Occasionally, individual dolphins may display surface-active behaviors (e.g., various in-air spins, slapping various body parts on the surface). In general, feeding is absent from bay behaviors. In the late afternoon, the dolphins move offshore into deeper waters for night time feeding.
Studies of the Leeward Oahu spinner dolphins have focused on general characteristics of the population for example their resting habitats, travel routes during times of the day, and general activity levels. (Lammers, 2004). Additionally, some work has been performed studying spinner dolphin acoustics (Lammers & Au, 2003; Lammers, Au, & Herzing, 2003; Lammers, Schotten, & Au, 2006). One published study examined long-term resights of a few spinner dolphins (Marten & Psarakos, 1999) and found individuals that had been photographed over 20 year periods.
Lammers, M.O., Schotten, M., and Au, W.W.L (2006). "The spatial context of free-ranging Hawaiian spinner dolphins (Stenella longirostris) producing acoustic signals" J. Acoust. Soc. Am. 119(2):1244-1250.
Lammers, M.O. (2004). “Occurrence and behavior of Hawaiian spinner dolphins (Stenella longirostris) along Oahu’s leeward and south shores.” Aqua. Mamm. 30:237-250.
Lammers, M.O., Au, W.W.L and Herzing, D.L. (2003). "The broadband social acoustic signaling behavior of spinner and spotted dolphins." J. Acoust. Soc. Am. 114(3):1629-1639.
Lammers M.O. and Au W.W.L. (2003). "Directionality in the whistles of Hawaiian spinner dolphins (Stenella longirostris): A signal feature to cue direction of movement?" Mar. Mamm. Sci. 19(2):249-263.
Marten, K., & Psarakos, S. (2000). "Long-term site fidelity and possible long-term associations of wild spinner dolphins (Stenella longirostris) seen off Oahu, Hawaii. Marine Mammal Science, 15, 1329-1336.