The Hawaiian spinner dolphin, Stenella longirostris: Effects of tourism.

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18 DAILY ACTIVITY CYCLE AND BEHAVIORS OF SPINNER DOLPHINS IN KEALAKE’KUA BAY, HAWAI'I. Spinner Dolphins, A Species Description Spinner dolphins occur in tropical and subtropical areas of the Pacific, Atlantic, and Indian Oceans (Mead et al. 1980, Leatherwood and Reeves 1983, Perrin 1990, Cooke 1991, Norris et al. 1994a), and have even been observed in the deeper areas of the mainly-enclosed Red Sea (Robineau and Rose 1983). Four subspecies of spinner dolphins have been described, including a dwarf form from the Gulf of Thailand (Perrin et al. 1989). Stenella longirostris orientalis and S. l. centroamericana are only found in the eastern tropical Pacific, while S. l. longirostris occurs in the tropics world wide (Perrin 1990). Although spinners typically inhabit deep offshore waters, the dwarf form from the Gulf of Thailand, the subspecies which occur along the Pacific coast of central America (S. l. centroamericana), and the subspecies near Hawai'i (S. l. longirostris), all approach shore at least occasionally (Leatherwood and Reeves 1983, Perrin et al. 1989, Perrin 1990). Most of the information on spinner dolphins comes from animals incidentally taken in the purse seine fishery for yellowfin tuna in the eastern tropical Pacific and from behavioral studies of a population off the Big Island of Hawai'i. The Hawai’ian spinner dolphins (from now on referred to simply as "spinner dolphins") occur as single-species aggregations near many Pacific Ocean islands (Leatherwood and Reeves 1983, Perrin 1990). They are slender animals characterized by a distinct tripartite color pattern. The light gray lateral field is sharply contrasted by a dark gray cape over the
19 dorsal surface and a white ventral surface (Figure 1). A dark eyeband extends from the rostrum to the flippers. Spinner dolphins of Hawai’i also exhibit a slight degree of sexual dimorphism. While females reach approximately 2 m in length and have a falcate dorsal fin, males are slightly larger and acquire secondary sexual characteristics of an erect dorsal fin and small post-anal keel upon reaching sexual maturity (Perrin 1990, Norris et al. 1994b). The population size of spinner dolphins around the island of Hawai’i has been estimated to be between 1000 (Würsig, Wells, Würsig and Norris1994) and 2334 animals (Östman 1994). These spinner dolphins follow a diel activity pattern that was described in detail by Norris and Dohl (1980), Norris et al. (1985) and Norris et al. (1994b). Figure 1. Spinner dolphin, Kealake’kua Bay, Hawai’i Daily Activity Cycle
Page 1 and 2: 1 CHAPTER I INTRODUCTION Documented
Page 3 and 4: 3 avoid areas within 10 km of activ
Page 5 and 6: 5 displayed a significant reduction
Page 7 and 8: 7 a linear model, the vessel explai
Page 9 and 10: 9 decreasing their surface times (C
Page 11 and 12: 11 Hector's dolphins, Cephalorhynch
Page 13 and 14: 13 a killer whale (Herman and Tavol
Page 15 and 16: 15 The Marine Mammal Protection Act
Page 17: 17 Dearden 1993, Thompson et al. 19
Page 21 and 22: 21 some areas consistently have mor
Page 23 and 24: 23 Aerial Behaviors Spinner dolphin
Page 25 and 26: 25 Norris and Dohl 1980). Increases
Page 27 and 28: 27 CHAPTER III OCCURRENCE AND BEHAV
Page 29 and 30: 29 Thirty-five observation days wit
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Page 37 and 38: 37 Most human activities that were
Page 39 and 40: Table 1 39
Page 41 and 42: 41 Discussion Norris et al. (1994 )
Page 43 and 44: 43 The correlation between number o
Page 45 and 46: 45 to perform. If the dolphins do,
Page 47 and 48: 47 times motor boats approached and
Page 49 and 50: 49 On one occasion, a swimmer obser
Page 51 and 52: Figure 11a, b 51
Page 55 and 56: 55 Figure 15. Square root of aerial
Page 57 and 58: 57 Figure 18a. Spinner dolphin surf
Page 59 and 60: 59 3.6 2 Square root of aerial acti
Page 61 and 62: 61 Figure 21a. Square root of aeria
Page 65 and 66: 65 Figure 25a. Square root of aeria
Page 67 and 68: 67 Figure 26. Square root of aerial
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69 Figure 28. Square root of aerial
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71 Discussion Swimmer and kayak dis
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73 morning than in the afternoon, t
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75 used by some boat operators resu
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77 reduced energy levels, then incr
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79 LITERATURE CITED Acevedo, A. 199
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81 Cooke, J. 1991. Classification a
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83 Gordon, J. and Moscrop, A. 1996.
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85 Montero, R., Martin, V., Heimlic
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87 Associates Inc., Bryan, Texas. F
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89 Wells, R. S. and Norris, K. S. 1
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