LONGLINE AND TROLL FISHING FOR TUNA IN THE CENTRAL EQUATORIAL 

 PACIFIC, JANUARY 1955 TO FEBRUARY 1956 



By 



Edwin S. Iversen— ' 

 and 



1/ 



Howard O. Yoshida 

 Fishery Research Biologist 

 Pacific Oceanic Fishery Investigations 

 Honolulu, T. H. 



The Pacific Oceanic Fishery Investiga- 

 tions (P O F I ) of the U. S. Fish and Wildlife 

 Service is conducting a survey of the tuna 

 resources of the central Pacific. This report 

 is concerned with the distribution and abun- 

 dance of yellowfin tuna in the Line Islands 

 region from January 1955 to February 1956, 

 as determined by longline fishing and surface 

 trolling. Summaries of results to date on the 

 general study of yellowfin abundance are in- 

 cluded, together with a report on the progress 

 made in a tagging progrann. In addition, the 

 results of Japanese connmercial longline fish- 

 ing in the equatorial region during 1955 are 

 briefly discussed. 



Seven reports on POFI longline tuna 

 fishing in the central equatorial region have 

 been published. The first five— describe the 

 results of exploratory longline operations and 

 provide general information on the biology of 

 the yellowfin, its abundance and distribution. 

 They also include studies of the longline as a 

 sampling tool, together with suggested changes 

 for greater efficiency. The most recent report 

 on fishing in this area (Iversen and Yoshida 

 1956) described the results of the first com- 

 mercial attempts to operate longlines in the 

 Line Islands region. 



The nine cruises which form the subject 

 of this report involved troll and longline fishing 

 in the Line Islands area by POFI vessels. 

 These cruises were planned to provide, as 

 nearly as possible, standardized observations 

 on fishing over a period of approximately one 

 year. It was hoped that information would be 



— The Marine Laboratory, University 

 of Miami, Coral Gables, Florida (formerly 

 Fishery Research Biologist, U. S. Fish and 

 Wildlife Service, Honolulu, T. H. ) 



- Murphy and Shomur a 1953a, 1953b, 

 1955, Murphy and Elliott 1954, and Shomura 

 and Murphy 1955. 



obtained to answer sonne of the questions raised 

 by the outcome of the connmercial expeditions of 

 1954 on the feasibility of connmercial tuna fish- 

 ing in the Line Islands area. Answers to these 

 questions require (I) abundance estimates of 

 the tuna population from a commercial view- 

 point, (2) further i ns i g ht into the interaction 

 between the environment and the tuna, and (3) 

 information on migration to be obtained by 

 tagging. Tagging is the most pronnising method 

 of demonstrating the relationship between small 

 yellowfin frequenting the coastal areas of the 

 various islands and the larger, more oceanic 

 deep-swimming yellowfin, and the degree of 

 association of the Line Islands population with 

 that of the rest of the Pacific. 



Daily sea surface temperatures taken 

 at the weather station at Christmas Island during 

 the period of this study are available. The data 

 indicate that the sea surface temperature was 

 unusually cold at Christmas Island during 1955. 

 The significance of this phenomenon in relation 

 to yellowfin catches is still being examined and 

 will be discussed in other POFI reports. 



The dates of the cruises are listed in 

 table 1. As only a portion of cruise 19 of the 

 Charles H. Gilbert was devoted to fishing in 

 the Line Islands area, the results have not been 

 analyzed here, although catch rates are given 

 in the Appendix. Cruise 25 of the Charles H. 

 Gilbert deviated from the standard pattern by 

 occupying a line of stations from 6°N. to 4''S. 

 latitude on 160°W. longitude, just west of the 

 Line Islands. Catch records and scientific names 

 of fishes discussed in this report are given in 

 the Appendix. 



ACKNOWLEDGMENTS 



Appreciation is expressed to the officers 

 and crews of the vessels Commonwealth , John 

 R. Manning, and Charles H. Gilbert for their 

 willing cooperation extending in many instances 

 well beyond the required performance of their 

 duties. Similarly, to the scientists and aids 

 who assiduously gathered the information con- 

 tained herein, we extend our thanks. 



