FISHERY BULLETIN: VOL, 77. NO. 4 



Figure 2. — Mobile observation 

 chamber (MOO at Kealakekua Bay. 

 The hatch is open to a cylindrical ob- 

 servation chamber that projects 1.5 m 

 below the hull. The observer views 

 through a 360° band of Plexiglas win- 

 dows. The operator steers and operates 

 the engine. 



tape recorder was connected to a hydrophone^ 

 mounted amidships and oriented forward. 



The craft was run by an outboard engine set in a 

 well aft. Stability was maintained by 900 kg of 

 lead blocks in a compartment below the observers 

 feet. 



Other underwater observations were made with 

 scuba, or by putting an observer with snorkle or 

 scuba below the bow of a slowly moving skiff, hold- 

 ing onto a bow painter. In this way the observers 

 could sometimes be towed among the animals and 

 even be jostled by them. A field station was estab- 

 lished at the village of Napoopoo on Kealakekua 

 Bay. 



Feeding was observed from skiffs and larger 

 vessels. Dip net samples were taken in the region 

 of feeding, and stomach analysis of such specimens 

 as became available to us were collected. The 

 squid and crustaceans in stomach samples were 

 identified by Richard Young of the Department of 

 Oceanography, University of Hawaii. Fish otolith 

 collections were lost through improper preserva- 

 tion. 



Recordings were made with a hydrophone de- 

 ployed from a stationary skiff located near a school 

 of animals or from the MOC. Monitoring was by 

 use of headphones. During our studies we were 

 fortunate to have William Schevill and William 

 Watkins of the Woods Hole Oceanographic In- 



^An Atlantic Research Corporation LC 32 hydrophone, a 

 Hewlett-Packard 466A preamplifier, and a Uher 4000s Vi-in 

 tape recorder composed the recording gear. The upper frequency 

 response of this system was approximately 20 kHz at 7'/i: ips. 



stitution establish a four-hydrophone array deep 

 in Kealakekua Bay. With this apparatus, three- 

 dimensional tracks of passing dolphins were ob- 

 tained that were of greater range and fidelity than 

 allowed by our simple gear. The experimental ar- 

 rangement of this array and recording charac- 

 teristics are described in Watkins and Schevill 

 (1974). 



Dolphin radiotracking used dolphin dorsal fin 

 radios (see Evans 1974) and a hand-held direction 

 finder. Dolphins were captured by a standard 

 head net. 



Throughout this paper we use the term "school" 

 to indicate all animals in a discrete area that move 

 together. Such schools are often composed of rec- 

 ognizable, discrete "groups" of animals clustered 

 together and moving and diving more or less in 

 unison. For instance, while the direction of move- 

 ment of larger schools may be the same for all its 

 parts, diving synchrony for all animals may be 

 quite extended and ragged, being composed of a 

 number of synchronously diving groups. Within 

 such groups one can sometimes recognize small 

 "subgroups" of a few (2 to perhaps 12) animals that 

 are often seen together, regardless of the group or 

 school composition around them. 



DISTRIBUTION 



Marine mammal collectors of the Sea Life Park, 

 an Hawaiian oceanarium, suggested that spinner 

 dolphins occur habitually at certain areas along 

 the island shores, while they are largely or wholly 



824 



