with the resulting information on their move- 

 ments, greatly outweighs the information that 

 can be gained by preserving or marketing them. 



The specific purposes of the POFI 

 equatorial tagging program were three. The 

 first was to obtain information on the relation- 

 ship between the snnall surface yellowfin (near 

 islands) and the large, deep-swimming yellow- 

 fin (open ocean) and thus to investigate the 

 possibility that recruitment into the larger size 

 groups comes principally from the smaller size 

 groups associated \vith islands. The extent of 

 such recruitment fronn the surface schools 

 around reefs into the longline fishery is of 

 course a very important consideration. The 

 second purpose was to examine the fluctuations 

 in abundance of longline yellowfin from the 

 standpoint of possible emigration. In other 

 regions a few recoveries of tagged fish have 

 done much to indicate the possible reasons for 

 abundance changes; an outstanding example is 

 the migration of albacore. A third purpose was 

 to learn about the age and growth of yellowfin. 

 The length of the fish is measured at the time 

 of tagging and this also provides an estimate of 

 its weight from the average length-weight rela- 

 tionship. As the fish is usually again measured 

 or weighed on recovery, an estinnate of gain in 

 length or weight for a known period of time is 

 thus obtained. With the accumulation of data 

 it should be possible to calculate the average 

 rate of growth and length of life of the species. 

 Such information is especially desirable in this 

 region, for a preliminary study of yellowfin 

 vertebrae indicates that this structure is not 

 suitable for age studies (Moore 1951); also size- 

 frequency analyses indicate a lack of modal pro- 

 gression with time, preventing an estimate of 

 growth (Iversen 1956). 



In these studies we used the so-called 

 "spaghetti" type of tag which has been described 

 by Wilson (1953) and which has beenused suc- 

 cessfully to trace the migrations of albacore 

 from California to Midway Island and Japan 

 (Blunt 1954, Ganssle and Clemens 1953). Briefly, 

 it consists of a white opaque plastic tube on which 

 is written in India ink the tag nunnber and direc- 

 tions for its return. For protection of the 

 markings this tube is encased in a clear plastic 

 tube of slightly larger diameter. The tag is 

 threaded through the dorsal region of the fish 

 just posterior to the second dorsal fin with a 

 special hollow needle and the loose ends are 

 tied by a figure-of-eight knot. 



During nine cruises in 1955-56 1,056 

 yellowfin, 21 skipjack, 1 little tunny, and 2 

 bigeye were tagged and released. Table 3 lists 

 the numbers of each species tagged and the 

 tagging locations for both longlining and trolling. 

 To date there have been two recoveries of tagged 

 yellowfin, both from the same general locality 

 in which they were captured and released. The 

 first (No. 1093) was caught by trolling and was 

 one of 2 fish tagged at Fanning Island on 

 S e pt e mb er 28, 1955. It was recaptured 

 at Fanning Island by a local resident on April 3, 

 1956, using handline gear and fishing at a depth 

 of about 50 fathoms. The fish had been at liberty 

 for 188 days. At release it measured 83.2 cm. 

 (estimated weight 25 1b.); at recovery it was 

 reportedto weigh 20 lb. The apparent shrinkage 

 in weight is doubtless due to errors of estimate. 



The second (No. 335 1) w a s caught by 

 trolling and was one of 16 tagged on October 8, 

 1955, at Christmas Island. It was recaptured 

 at Christmas Island on August 2, 1956, by a 

 local resident presumably by handline, and was 



Table 3. --Numbers of tuna tagged in the Line Islands, March 1955 to February 1956 



11 



