FISH SCHOOLS AND BIRD FLOCKS IN THE CENTRAL PACIFIC OCEAN, 1950-1961 



By 



Kenneth D. Waldronl^ 

 Fishery Biologist (Research) 

 Bureau of Commercial Fisheries Biological Laboratory 

 Honolulu, Hawaii 



INTRODUCTION 



A major objective of many cruises of the 

 Bureau of Commercial Fisheries research ves- 

 sels operated by the Biological Laboratory in 

 Honolulu has been to investigate the distribution 

 of tunas in the central Pacific. The presence of 

 tunas in oceanic areas is detected by use of var- 

 ious fishing techniques and by visual observa- 

 tions of schools. The presence of tuna schools at 

 the surface is often signaled by closely associ- 

 ated bird flocks which feed on the same small 

 forage organisms that are at the surface or are 

 driven to the surface, presumably by feeding tuna. 

 The bird flocks are visible at a greater distance 

 than the fish schools and are therefore often uti- 

 lized by fishermen to locate schools. 



Between 1950 and 1961, vessels of the 

 Honolulu Laboratory and Laboratory-chartered 

 vessels made 177 cruises in waters of the Pacific 



Ocean generally bounded by the American west 

 coast, latitudes 20° S. and 50° N., and longitude 

 165° E. (fig. 1). These cruises were for the pur- 

 pose of exploring the distribution and abundance 

 of fish, especially tuna, and to collect oceano- 

 graphic data pertinent to the environment in which 

 tuna live. With few exceptions, a watch was rou- 

 tinely kept for fish schools and bird flocks, and 

 all sightings were recorded. 



This report summarizes by time-area units 

 the sightings made during 128 of these cruises 

 (table 1) within that portion of the total area 

 bounded by latitudes 20° S. and 30° N., and longi- 

 tudes 110° W. and 180°(flg. 1). It was within this 

 area that the major amount of effort was expend- 

 ed and the major portion of the schools and flocks 

 observed. 



METHODS 



A general method of searching for fish 

 schools, often referred to as "scouting," was 

 followed from 1950 to 1961. Royce and Otsu 

 (1955) described this method in detail and pre- 

 sented an evaluation of its efficiency. Briefly, 

 the vessel's crewman on wheel watch maintained 

 a lookout during daylight hours for birds and 

 other signs of fish schools and recorded his 

 observations. The information recorded included 

 date, time, position of the vessel at time of 

 observation, estimates of the number of birds 

 in the flocks, general types of birds, and if fish 

 were associated with the birds, the species of 

 fish, size of fish, and size of the school. The 

 crewmen were, for the most part, experienced 

 fishermen, who could distinguish bird flocks at 



distances up to 4 miles and at closer range 

 identify the various birds and fish encountered 

 in the central tropical and subtropical Pacific. 

 In addition to maintaining a record of the flocks 

 of birds and schools of fish, the crewmen also 

 kept count of the numbers of individual fish, scat- 

 tered birds, and aquatic mammals sighted. 



Groups of birds were designated as flocks 

 or as scattered birds on the basis of their behav- 

 ior. A flock, ranging in numbers from a few to 

 several hundred individuals, behaves as a unit, 



-^ Present address c/o Bureau of Commercial 

 Fisheries Biological Laboratory, 2725 Montlake 

 Blvd., Seattle 2, Washington. 



