A SUMMARY OP SIGHTINGS OF FISH SCHOOLS AND BIRD FLOCKS 

 AND OF TROLLING IN THE CENTRAL PACIFIC 



By 



Garth I. Murphy and Isaac I. Ikehara 



Fishery Research Biologists 



Pacific Oceanic Fishery Investigations 



U. S. Fish and Wildlife Service 



There are three Important types of tuna fisheries In the Pacific, two of which 

 operate by finding and catching the fish on or near the surface. The third, long- 

 line fishing, widely practiced by the Japanese in the western Pacific, operates by 

 catching the large deep-swimming tunas that rarely appear at the surface and are 

 never seen prior to capture. On the other hand, llvebalt fishing and purse seining, 

 the former Important both off Japan and the Americas, and the latter Important only 

 off the Americas, Involve locating schools of fish before capturing them. As the 

 extent of the resources of these surface and deep-swlmmlng tunas in the central 

 equatorial Pacific was little known, the Pacific Oceanic Fishery Investigations 

 (POFI) has attempted to evaluate their fishery potential by studying their abundance 

 and their relation to the ocesinic circulation and productivity. This report, one of 

 several resulting from these investigations, deals with the abundance and distribu- 

 tion of surface schools of tuna in the central equatorial Pacific. 



Because of the vastness of the area to be explored and the small number of 

 vessels available for the various types of fishing and oceanographic cruises that 

 had to be made, it has been possible to cover only the most promising parts of the 

 region with cruises expressly planned to locate and fish for surface schools. In 

 order to secure information from a much broader area, systematic searching for 

 visible indications of tuna schools and trolling to detect the presence of fish 

 have been done routinely during all daylight runs of POFI vessels, whatever the 

 primary objectives of the cruises on which they were engaged. This method of sur- 

 veying essentially parallels the scouting techniques of the commarcial surface 

 fisheries, for most schools fished by purse-seine and llvebalt boats are located 

 oy seeing the fish in the water, by noting the presence of birds and other animals 

 known to associate with tuna, or by capturing tuna on trolling lines. 



This report is a biological evaluation of all the observations on surface 

 tunas from the Inception of the program In 1950 to April 1953 with the exception 

 of the observations currently accumulating from a study around the Hawaiian Islands 

 (Royce and Otsu 1955). The results significant to commercial trolling and llvebalt 

 fishing have already been reported (Bates 1950, Ikehara 1953) and this aspect Is 

 not reconsidered here. In essence, we summarize and Interpret what was seen from 

 the bridge and what was caught from the stem during 546 days when research vessels 

 were under way through the tropical and subtropical waters of the central Pacific. 



The observations on fish schools and bird flocks are arranged to furnish 

 comparisons among the various Island groups in the central Pacific and comparisons 

 between the vicinity of land and the open ocean, and to estimate variations in 

 abundance associated with different periods of the year. The results of trolling 

 are organized in the same manner as the sighting records. Finally, the resulting 

 estimates of tuna abundance around certain islands and in limited portions of the 

 open ocean are compared with the standing crop of plsinkton, in order to investi- 

 gate the hypothesis that a larger supply of basic food should be associated with 

 a larger population of animals farther up the food chain. 



The recording of the numbers and types of fish schools and birds seen while 

 the vessels were under way has usually been a duty of the wheel watch under the 

 guidance of the scientist In charge, and credit is due the officers and fishermen 

 of the research vessels John R. Manning , Hugh M. Sml th , Charles H. Gilbert , and 

 the charter vessel Cavallerl for the keen observation and the systematic recording 

 of what they saw. Surface trolling and the maintenance of appropriate records of 

 this operation have been the responsibility of the various scientific field 

 parties. 



