Figure 3. — Monthly landings of blue marlin and striped 

 marlin from 1963 to 1970 in Hawaii. 



catches of bigeye tuna are made during the winter 

 and spring (June, 1950; Otsu, 1954; Shomura, 1959). 

 This suggests that striped marlin and bigeye tuna 

 may be responding to a different set of environmen- 

 tal factors from the blue marlin and yeilowfin tuna. 

 Strasburg (1970) has suggested a relation to the food 

 supply to explain the complementary abundance of 

 striped marlin and blue marlin around Hawaii. He 

 noted that blue marlin fed largely on skipjack tuna, 

 which were more abundant in the summer. This may 

 account for the larger numbers of blue marlin during 

 the summer. 



Further evidence that the blue marlin are indeed 

 responding to the presence of their prey can be seen 

 in the relation between the landings of skipjack tuna 

 and blue marlin in Hawaii (Fig. 4). Generally speak- 

 ing, good catches of blue marlin corresponded to 

 good catches of skipjack tuna. The situation in 1965, 



however, did not conform to the general trend. The 

 reason for this is not known. 



CATCH PER UNIT OF EFFORT 



The CPUE (catch per unit of effort) for striped 

 marlin and blue marlin was determined to see if 

 CPUE had any effect on the monthly landings. As 

 Shomura (1959) indicated, measures of effort such as 

 number of hooks or baskets of gear fished, are not 

 readily available for the Hawaiian longline fishery. 

 Thus for his analysis of the abundance of tunas 

 around Hawaii, he used the number of trips as a 

 measure of effort. Following Shomura, the number 

 of trips was used to calculate CPUE. here given as 

 number of fish caught per trip on a monthly basis 

 (Fig. 5). 



The catch rates for striped marlin and blue marlin 

 showed the same trends as the monthly landings. 

 Similar to the monthly landings blue marlin catch 

 rates usually peaked from July to September. Dur- 

 ing the period from 1961 to 1969, however, the an- 

 nual summer peak in the catch rates has shown a 

 small but steady decline. 



Similarly, the monthly catch rates of striped mar- 

 lin showed the same trends, although the fluctua- 

 tions were not as pronounced as the monthly land- 

 ings. As did the monthly landings, the monthly 

 catch rates for striped marlin showed two peaks 

 annually, usually one in the spring and the other in 

 the fall. In contrast to the blue marlin, the annual 

 peaks in the monthly catch rates for striped marlin 

 from 1961 to 1969 have increased slightly. 



SIZE OF FISH 



The quarterly weight-frequency distribution of 

 striped marlin by sex is shown in Figure 6. The size 



BLUE MARLIN LANDINGS (METRtC TONS) 



Figure 4. — Relation between landings of skipjack tuna 

 and blue marlin in Hawaii. 



Figure 5. — Monthly catch per trip of blue marlin and 

 striped marlin. 



299 



