Effects of vessels and swimmers on behavior of Hawaiian spinner dolphins (Stenella longirostris) in Kealake‘akua, Honaunau, and Kauhako bays, Hawai‘i

Studies of the influence of boat traffic on small cetaceans have shown that the animals exhibit behavioral responses, including changes in swimming speed, diving and aerial behavior, vocalization patterns, and movement patterns (e.g., Au and Perryman 1982; Janik and Thompson 1996, Constantine et al. 2004, Delfour 2007). Janik and Thompson (1996) cautioned that such disruptions could cause longer-term changes in behavior, ecology, or status of a population, including avoidance of certain areas or increases in mortality rates. In some cases, injury or death of dolphins (Stone and Yoshinaga 2000) and injury or death of humans (Shane et al. 1993, Santos 1997) have been reported. Recent studies have begun to discover dolphin avoidance of high-traffic areas (Lusseau 2004, 2005; Bejder et al. 2006a). Concerns have been raised about the effects of vessel and swimmer traffic on spinner dolphins (Stenella longirostris) resting in Hawaiian bays (Lammers 2004, Delfour 2007). Vessel and swimmer traffic in Kealake‘akua and other Hawaiian bays has increased (Östman-Lind et al. 2004, Delfour 2007) since the original studies of Ken Norris and his colleagues (Norris and Dohl 1980; Norris et al. 1985, 1994). Spinner dolphins in the bays attract people, and dolphin disturbance as a result of increased swimmer and boat traffic needs to be assessed. Spinner dolphins use Hawaiian bays as havens in which to rest during the day (Norris et al. 1994), so disturbance by vessels and swimmers may affect their activity budgets and fitness. Concerns regarding dolphin disturbance have caused NOAA Fisheries to propose new regulations for interaction with Hawaiian spinner dolphins (Department of Commerce 2005, 2006). In response to these concerns, the purpose of our study was to document behavior of Hawaiian spinner dolphins in three bays with respect to vessel and swimmer traffic.