FISHERY BULLETIN: VOL 77. NO, 4 



of air were noted issuing from the blowhole cor- 

 ners in spinners near the capsule. Whistles and 

 chirps could often be heard concurrently. Some- 

 times, during active chases one or more animals 

 would release a large bubble of air underwater, 

 which boiled upward to the surface. Pryor (1973) 

 has correlated such behavior in captive animals 

 with frustration. 



Spinner dolphins change school swimming pat- 

 terns in relation to weather. In rough seas, groups 

 of dolphins appear to ride the swells and breaking 

 waves that sweep toward the Kona coast. On one 

 such occasion, while we "hove to" in a rough sea, 

 perhaps 100 spinners passed us. They were di- 

 vided into small groups of less than a dozen ani- 

 mals. These groups swam tightly together and 

 often could be seen racing down the foreslope of the 

 waves, sometimes breaking the water together 

 and sometimes staying wholly within the wave. 

 Such behavior is commonly seen in other cetacean 

 species (Norris and Dohl in press). 



Sound Emmissions 



A detailed study of spinner dolphin sound emis- 

 sions will be presented in a future paper. A few 

 observations are appropriate here. 



There is a marked diurnal fluctuation in the 

 kind and amount of spinner dolphin vocalization 

 (Powell 1967). Alert schools produce an array of 

 sound types such as clicks, pure-tone whistles or 

 "squeals," and a variety of burst pulse signals that 

 can be described by such terms as barks, moos, 

 chirps, etc. The clicks are of considerably lower 

 intensity than either the whistles or the burst 

 signals (Watkins and Schevill 1974), and the 

 clicks may be more tightly focused. 



Resting schools are nearly silent, emitting al- 

 most entirely clicks and even these are sporadic. 

 Simultaneous with arousal, vocalizations rise in 

 variety and abundance. Whistles and burst pulse 

 signals can be heard quite long distances under- 

 water. With WatkinsandSchevill, we wereableto 

 station ourselves outside Kealakekua Bay and 

 hear whistles and various burst pulse signals from 

 a group of spinners swimming close to the cliff", 

 approximately 2 km distant. Thus, a school of dol- 

 phins swimming outside Kealakekua Bay during 

 longshore movement would be able to detect ani- 

 mals deep in the bay without entering it. It is 

 possible that the schools we have seen passing the 

 bay when others occupied it may have been 

 excluded by acoustic signals. 



846 



No context-specific sound signals have been 

 identified by us, except that it seemed clear that 

 clicks were emitted concurrent with the inspection 

 of the environment. The likelihood of context- 

 specific acoustic signaling in the daily events in 

 the school, however, seemed high. For example, 

 synchronous diving in very widely dispersed 

 schools, or simultaneous turning of an entire 

 school at dusk, are unlikely to be visually cued 

 (though it is not impossible). The sounds produced 

 by aerial behavior have, in a few instances, been 

 picked up by our listening gear. Tailslaps are 

 especially loud, while spins (which we have re- 

 corded in captive situations) produced a lower in- 

 tensity signal quite different in character. 



Predators 



Hawaiian spinner dolphins seem to be attacked 

 with some frequency by sharks. Several of the 

 scarred animals we cataloged had obviously been 

 wounded by large sharks. Lunate rows of tooth 

 marks, especially on the tail region, some appar- 

 ently from sharks with a 12-15 in (31-38 cm) gape 

 were noted. In one case it seemed that the entire 

 tailstock had once been in a shark's mouth. Nicked 

 or tattered dorsal fins may also have been pro- 

 duced by shark bite. 



Subcircular scars somewhat larger than a silver 

 dollar commonly seen on tropical and subtropical 

 cetaceans are common on spinner dolphins. Jones 

 ( 197 1 ) suggested that these scars are produced by 

 the small squaloid shark Isistius brasiliensis. This 

 small shark occurs with scattering layer or- 

 ganisms, is bioluminescent over its entire body, 

 and is thought to be a squid mimic. Feeding dol- 

 phins may be attracted to it, and when close, the 

 shark may swim to the dolphin, attach itself, and 

 then scoop out a disc of blubber and flesh with its 

 peculiar dental and branchiostegal apparatus. 

 The shark has erect cutting teeth only in the lower 

 jaw and a jaw apparatus that allows it to attach 

 and push the teeth through the flesh of its prey like 

 a cookie cutter. The shark may bite while facing 

 the tail of the porpoise and be swTjng around in the 

 current, cutting as it goes. Discs of dolphin blubber 

 have been found in the stomachs of this shark 

 (Jones 1971). We have seen fresh wounds of this 

 shape and size several times, including some com- 

 pletely through the blubber to the flesh beneath. 

 Nearly every adult dolphin bears some scars of 

 this sort, on some part of its body. We have never 

 seen such scars on the appendages or head, though 



