TUNA OCEANOGRAPHY IN THE 

 EASTERN TROPICAL PACIFIC 



by 

 Maurice Blackburn and Associates 



ABSTRACT 



A report on 3 years of oceanographic investigation in the eastern tropical 

 Pacific Ocean, with the object of understanding environmental properties and 

 processes responsible for changes in the abundance and distribution of yellowfin 

 and skipjack tuna in a way that may lead to prediction of such changes, is presented. 

 The program included field observations by means of cruises and statistical analy- 

 sis of physical, chemical, and biological measurements obtained on cruises. It 

 also included a laboratory-experimental program to give leads for developing field 

 and statistical work programs, and it encompassed development and testing of 

 moored unmanned instrumented ocean stations to collect and record ocean data. 



INTRODUCTION 



United States fishermen catch yellowfin tuna 

 (Neothunnus macropterus) and skipjack tuna 

 (Katsuwonus pelamis) by live-bait and purse seine 

 fishing in the eastern tropical Pacific Ocean 

 and adjacent waters. The annual catch was 

 fairly stable in amount over the past decade 

 at a level near that of the best year of the 

 fishery, but it declined in value from about 

 1953 as a result of the increasing availability 

 in the domestic market of lower-priced tuna 

 from foreign fisheries (Power, 1959). It there- 

 fore became necessary to consider ways of 

 cutting costs in the United States fishery, and 

 reduction of time spent in searching for tuna 

 seemed to offer attractive possibilities. Be- 

 lieving that such reduction of time could even- 

 tually be achieved if the effects of the ocean 

 environment on the distribution and abundance 

 of tuna were understood, the Bureau of Com- 

 mercial Fisheries in 1957 contracted with the 

 Scripps Institution of Oceanography for an 

 "Investigation of oceanographic and climatic 

 influences on the distribution and behavior of 

 tunas in the eastern tropical Pacific." The 

 period of the contract was from June 20, 1957 

 to June 30, 1960. 



The investigation followed a proposal made 

 in 1957 by the Scripps Institution of Ocea- 

 nography, which read in part: 



The general question toward which investigations under this 

 contract will be aimed is: "At what times and places in liie eastern 

 tropical Pacific can the tuna fleet find schools of tuna in a catchable 



condition? " Many places are already known at wliich good catches 

 may be expected at certain times. However, in some years ttiese 

 expectations are not realized: fishing in a particular place at the 

 right lime does not yield good catches. It will be a primary aim of 

 these sttidies to select one or moreareasand try to reach an under- 

 standing of the chain of events--air circulation, water circulation, 

 primary production, secondary production, catchable tuna. If tlie 

 cliain of events deiernhning the presence or absence of catcliable 

 tuna at a particular time and place is understood. It sliould he 

 possible to predict this and thus be of direct aid in advising the 

 fisliermen what areas at what times will be most productive. It 

 sliould be emphasized that it is not predicted that a reliable, working 

 forecasting service will be in existence at the end of tliree years. 

 The accumulation of as much information toward that end as time and 

 resources will allow will be a goal, however. 



This paper is a short, simplified version 

 of the report submitted to the Bureau on the 

 research performed under the contract. The 

 names of the investigators are given in the 

 sections of the paper for which they were 

 responsible. 



The Bureau-financed research program has 

 been known as Scripps Tuna Oceanography 

 Research (STOR). Its work is continuing under 

 another contract from the Bureau of Commer- 

 cial Fisheries. 



The following persons were paid from STOR 

 funds for periods of at least one year: 



Dr. M. Blackburn, Research' Biologist (Pro- 

 gram Director), September 1957-June 1960. 



Dr. W. S. Wooster, Associate Research Ocea- 

 nographer (half-time), July 1958-June 1960. 



Dr. G. W. Groves, Assistant Research Ocea- 

 nographer, January 1958-August 1959. 



Mr. R. W. Holmes, Assistant Research Biolo- 

 gist, July 1957-June I960. 



