indication, however, that the steel gear has a lower 

 catch rate than fabric gear . A comparison of the 

 two, made on John R. Manning cruise 20, shows 

 that the steel line caught about the same number 

 of small yellowfin, but that it caught relatively 

 fewer medium and large yellowfin than the fabric 

 gear (fig. 2). The steel gear probably does not 

 offer the resiliency to the struggles of the fish 

 that the fabric gear does, hence a higher propor- 

 tion of the larger tunas escape. 



The amount of shark damage varies consi- 

 derably from cruise to cruise. The numbers of 

 shark -damaged yellowfin are included in calcula- 

 tions of abundance for each cruise, but, of 

 course, should not be counted when calculating 

 the number of marketable fish. 



VESSEL EFFICIENCY 



It has been frequently observed that with 

 equivalent fishing effort some vessels are able 

 to produce good catches while others fishing 

 under seemingly the same conditions and in the 

 same general area do poorly. The reasons for 

 this, perhaps, lie in the skill, experience, etc., 

 of the fishermen involved. In an intensive fish- 

 ery individual differences in experience will be 

 smoothed out in the seasonal or annual averages. 

 In 1954, only eight vessels took part in longline 

 fishing in the area of study, and one of these 

 made only a single trip; also the waters, and, in 

 some instances, the fishing method, were un- 

 familiar to the fishermen. Hence it is possible 

 that some of the variation among catches made 

 at different times of the year resulted from 



differences among vessels and not entirely from 

 a seasonal variation in the abundance of yellow- 

 fin. 



Despite this possibility, it appears that 

 differences among vessels did not seriously 

 affect the catch rates, since there were only 

 gradual changes in the catch rates between con- 

 secutive cruises , and when two or three vessels 

 fished simultaneously, as did the North Am erican 

 and the Alrita, the catch rates were in general 

 similar (fig. 3). The 95-percent fiducial limits 

 estimated by Murphy and Elliott (1954) for long- 

 line catch rates, if assigned to the rates of each 

 vessel, would doubtless overlap. 



Differences among local fishing areas could 

 also affect the catch rates. In Hawaii, for ex- 

 ample, Otsu (1954) found that certain longline 

 boats fished in a certain area whether productive 

 or not, while others fished in areas which were 

 known to be the most productive at a particular 

 season. On the basis of the meager data avail- 

 able from the Line Islands area it appears that 

 yellowfin move around these rather small islands 

 in a more or less random manner . This, coupled 

 with the fact that the vessels moved about from 

 day to day, makes it very doubtful that location 

 of fishing biased the catches. 



YELLOWFIN ABUNDANCE 

 Latitudinal Variation 



In February to April 1954 the Charles H . 

 Gilbert (cruise 15) occupied fishing stations on 



NORTH AMERICAN CATCH 

 ALRITA CATCH 



JAN 



FEB 

 North American Cr. I 

 Alrita Cr I 



MAR 



North American Cr 2 

 Alrita Cr 2 



Figure 3. --Daily variability of yellowfin catch between the North American and the Alrita in the 

 Line Islands. 



