drifts of the raft near tlie island of Hawaii, fish accumulated 

 more rapidly during daylight hours than at night and while the 

 raft was drifting than when anchored (fig. 6). Apparently vision 

 played an important role in the ability of fish to locate the 

 raft. When the raft was anchored, the current flowing by it 

 swept the small fish away. When the raft was adrift, a loose 

 community of fishes and of other animals accumulated around 

 it and formed a small area in the sea with associations and 

 events similar to those of inshore environments with sub- 

 strates. 



Underwater observations emphasize the fact that although 

 experiments carried out in shoreside facilities provide val- 

 uable information on the behavior of pelagic fishes, it is im- 

 perative that these fishes also be observed in their natural 

 environment. Such observations need not be restricted by the 

 limited capabilities of the human eye beneath the sea: sonar 

 is a valuable research tool presently being used to study the 

 behavior of some sea fishes. A survey was made to determine 

 the characteristics required of a sonar gear specifically for 

 tuna studies. The study indicated that existing instruments 

 were not entirely satisfactory for field studies of tuna. The 

 sound-reflecting qualities of these fish and their relatively 

 fast speed, require very high resolution and information-rate 

 characteristics. A frequency-modulated sonar is being de- 

 signed that has these features and will permit a continual 

 transmission of impulses that can trace such fast-moving fish 

 as the tuna. This sonar gear will enable us to undertake 

 studies on the form, movements, and social structure of tuna 

 schools. 



Trade -Wind Zone Oceanography 



The Trade-Wind Zone Oceanography Program began at the 

 Biological Laboratory in October 1962, as an outgrowth of a 

 study of the Hawaiian oceanographic climate^' in which changes 

 in the distributionof temperature and salinity were interpreted 

 in terms of heat exchange across the sea surface and of water 

 motion. Primary objective of this program is to investigate 

 further the dynamic processes of surface waters in the Pacific 

 trade-wind zone. The program encompasses an experiment 

 consisting of a design and planning phase, which is described 

 in this report; a 2-year, multiple-ship field phase; and an 

 analytical and evaluation phase. 



These studies will contribute to our understanding of the 

 oceanographic climate in the trade-wind zone and may show 

 that changes in distribution of water properties can be used 

 to monitor changes in the oceanographic climate and to fore- 

 cast favorable fishing conditions. The significance of these 

 studies, however, extends beyond fishery problems. Studies 

 of the dynamic processes of the trade-wind zone also will 

 provide new knowledge on the Pacific heat engine which con- 

 trols both continental and oceanographic climates. The trade- 

 wind zone represents a region of net annual heat gain; there- 

 fore, the amount of heat gain and the rate at which heat is 

 carried into higher latitudes affect long-term climatic trends. 



While planningfor future field activities, we have proceeded 

 with the investigation itself and have begun preliminary studies. 

 During this report period these studies have included the eval- 

 uation of Koko Head surface temperature and salinity data, 

 the examination of parameters in the wind fields over the 

 North Pacific, and the examination of thermocline structure. 



In the studies of surface water processes, we have continued 

 to measure surface temperatures and salinities each week at 

 Koko Head, Oahu. Our purpose has been to learn more of the 

 association between changes in the distribution of properties 



i/seckel, 1962, Fishery Bulletin 193. 



