CHARLES H GILBERT CRUISE 1 1 



CHARLES H GILBERT CRUISE 13 



AREA I 



EAST AND WEST ARMS 



JUN 13,14 



DIRECTION TRAVELED, 

 OBSERVED LESS THAN 

 10 MINUTES 



MILES 



Figure 8. --Direction and distance 

 moved in 10 minutes by schools 

 seen on runs where a Doppler effect 

 was suspected during the April and 



June cruises. The number in the 

 center is the total number of schools 

 seen; the number of arrows indicates 

 the number of schools which nnoved. 

 Distances are indicated from the 



circle, not its center. 



in all parts of each sector, but they were consistently less 

 abundant to the northeast. Also, the abundance decreased 

 from month to month. 



The exceptional station where more schools were 

 sighted on the September and October cruises was located 

 about 80 miles west of Hawaii and 110 miles south of 

 Oahu. The abundance of tuna here seems the more signi- 

 ficant because it is near an eddy which is indicated in our 

 preliminary analysis of oceanographic observations. This 

 eddy, which is now being made the subject of more detailed 

 study, is a counterclockwise one, in the center of which 

 the thermocline rises to less than 100 feet of the surface. 

 It is suspected that this eddy may somewhat enrich the 

 waters and indirectly create more food for the skipjack. 



SEASONAL TRE^fD 



The seasonal trend in the landings of skipjack is 

 fairly constant and is well known to everyone in the local 

 fishing industry. With minor variations, the low landings 

 of the winter months increase gradually to a peak in the 

 summer and decline again to a low in the winter. The pat- 

 tern during 1953 was nearly typical, with a peak in June 

 and a secondary peak in August. Therefore, when our 

 scouting results indicate a markedly different seasonal 

 pattern of abundance (fig. 11), with a peak in April and 

 much lower abund£uice during the fall months, it would 

 appear to be a matter for further study. 



First, we must consider the reliability of the esti- 

 mates of abundance from our scouting results, and since 

 in most cases a considerable amount of scouting was done, 

 the question appears to become one of whether the areas 

 covered by our scouting were representative of the areas 

 being fished by the fleet. The cruises from which we have 

 scouting data have varied considerably in length, the 

 scouting frequently has been incidental to other operations, 

 and the areas covered have varied considerably among 

 cruises. However, on the cruises in February, April, 

 June, September, October, and November scouting was 

 the major objective and large ctreas were covered. This 

 scouting extended far outside the range of the fleet, but it 

 revealed a fairly uniform geographic distribution of schools 

 and the results should be similar to the experience of the 

 fleet. Also, the seasonal pattern indicated by these major 

 cruises is supported by the scouting results of GILBERT 

 cruises 3, 6, 8, and 12, during which scouting was inci- 

 dental and much more restricted in area. 



Therefore, it seems clear that our scouting results 

 are representative, and yet they differ markedly from the 

 trends in the commercial catch. The principal and nnost significant difference is the peak in 

 abundance indicated by the April scouting, which does not correspond to a peak in the catch, and 

 for an explanation we turn to more detailed data from the commercial fishery itself during the 

 periods of GILBERT cruises 11 and 13 in April and June. Table 13 is a summary of data from 

 interviews with captains obtained by the Division of Fish and Game, Board of Commissioners of 

 Agriculture and Forestry, Territory of Hawaii. These records show that the commercial fisher- 

 men also saw slightly more schools per day during April, but these schools were mostly small 



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