was uncertainty about the commercial value of 

 such fishing in this region. Bates (1950) con- 

 cluded that the Line Islands ' population of yellow- 

 fin was sufficiently abundant during the spring 

 of 1950 for commercial exploitation by limited 

 fishing effort. The results of occasional surveys 

 by trolling in the Line Islands are briefly reviewed 

 by Murphy and Ikehara (1955). These authors 

 utilize the catch rates of Bates (1950) and later 

 surveys by POFI vessels amounting to 890 line 

 hours in the Line Islands area (defined as 0-60 

 miles from land) and compare them withyellowfin 

 catch rates reported from Hawaii by Welsh (1950) 

 and Tester ( 1952). Murphy and Dcehara's analysis 

 shows a higher catch rate of yellowfin from the 

 Line Islands than from Hawaii. 



In drawing conclusions from the results 

 presented here, we have assumed that differences 

 ineffectiveness of the various lures are insigni- 

 ficant and have not materially affected the catch 

 rates. Lures were interchanged frequently so 

 any effect produced by differential efficiency of 

 lures should not be important. Variation in the 

 number of lines fished during these cruises is 

 likewise believedto have had such a minor effect 

 on abundance figures that it is not considered. 

 All vessels trolled either 5 or 6 lines, and it 

 was a very rare occasion when all lines had 

 simultaneous strikes. 



The 1955-56 trolling results show varia- 

 tions of sufficient magnitude in certain aspects 

 to warrant detailed examination, though overall 

 catch rates for the period are low. Possible 

 sources of variation are the time of day of fish- 

 ing, seasonal change in catch rate, and the area 

 of catch. On some cruises there is an indication 

 of slightly higher catch rates in the morning 

 than in the afternoonand early evening, but this 

 is not consistent among cruises (fig. 8). The 

 indication is of interest, however, since Reintjes 

 and King (1953)found that yellowfin captured in 

 the afternoon by trolling and live -bait fishing 

 had more food in their stomachs and fewer empty 

 stomachs than those captured in the morning. 



They conclude that feeding takes place through- 

 out daylight hours. Bates (1950) found that troll 

 catches of yellowfin did not vary significantly 

 with time of day. 



In respect to seasonal variation, yellow- 

 fin catch rates were highest in March and April 

 (1.3 to 7.3 fish per hour) for all islands and 

 generally low the rest of the year (usually < 2 

 fish per hour) as shown in figure 9. The July 

 and August catch rates were extremely low 

 (usually < 1 yellowfin per hour). 



The data shown by cruises and trolling 

 areas (fig. 10) demonstrate that generally 

 yellowfin were more abundant at Palmyra and 

 Kingman Reef (6°N. ) than at Christmas (2''N. ). 

 Bates (1950) also reported this phenomenon. 

 At present we have no explanation for this differ- 

 ence in abundance. 



There are two important considerations 

 from this analysis of our trolling data. First, 

 the abundance of yellowfin in this area during 

 the period studied was too low to encourage 

 commercial exploitation of small tunas by this 

 method of fishing. Second, there maybe seasonal 

 trends in abundance, for there were higher 

 catches in March and April than during the 

 remainder of the year. Table 2 contains a 

 summary of trolling results for three different 

 periods in the Line Islands area. Rather low 

 catch rates were experienced during two of the 

 time periods, i.e., October 1950 to April 1953 

 and March 1955 to February 1956. A slightly 

 better catch rate was obtained during April to 

 June 1950. The catch rate for this period, how- 

 ever, is not directly comparable with the other 

 two, for fishing was confined to only a few 

 months. Although only speculation, it seems 

 that the abundance (judging by the troll catch 

 rates) of the small yellowfin around the islands is 

 too low to comprise the principal source of 

 recruitment for the extensive population 

 of large, deep-swimming yellowfin in this area. 



Table 2. --Results of trolling in the Line Islands 



- Murphy and Ikehara (1955) reported 890 line-hours of trolling using 4-6 lines. 

 The number of hours trolled was obtained by dividing 890 line-hours by five, the average 

 number of lines trolled. 



8 



