The Hawai'ian spinner dolphin, Stenella longirostris: effects of tourism

Abstract

Human activities and spinner dolphin behavior were observed in Kealake'kua Bay, Kona coast, Hawai'i, from 28 August, 1993 to 7 July, 1994. Data were collected from an observation site 55 m above mean low water on a steep slope at the eastern edge of the bay. Dolphins occurred within Kealake'kua Bay on 135 of 232 observation days, or 58% of the time. Estimated school sizes ranged from 4 to 90 individuals, with a mean of 33. As found in earlier studies, dolphins used the bay for low-level social activities and rest, with early mornings and afternoons characterized by higher states of apparent alertness than during mid-day. Humans, especially females, entered the bay significantly more on days when dolphins were present than when they were not. Thirty-five days with 5 hours or more of continuous observations with Beaufort sea state 3 or less were selected to compare surfacing behavior and frequency of aerial activities with different types of human activities (comparisons by one-way MANCOVA and Scheff ̌test). The human activities of swimmers, kayaks, and motor boats, alone or in combination, had no apparent impact on dolphin surfacing behavior in the morning. However, in the afternoon, dolphins were more likely to surface asynchronously than synchronously in the presence of each activity, and aerial activities were higher than without humans. Dolphins used Kealake'kua Bay on 21% fewer days in 1993-94 than 1979-80. This could be due to ecological factors, spinner dolphin demographics, or human influences. Spinner dolphins also showed less aerial activity during this than the earlier work, indicating a potential reduction in energy levels. Effects of human activities could be detrimental by disrupting critical behaviors such as reproduction, feeding and rest. It is strongly recommended that human use of Kealake'kua Bay be more strictly controlled, and that a major section of water be set aside where dolphins are not to be disturbed.