12 



!8 



ap 



4 ^ 



1952 1953 1954 1955 1956 1957 1958 1959 I960 1961 1962 

 YEAR 



Figure 13. --Total annual catch, catch per standard 

 effective trip, and relative effective fishing 

 intensity, for skipjack in Hawaii, 1952-62. 



Another aspect of the program concerned itself with the 

 distribution of large fishes such as tunas, martins, and sharks 

 in the transition waters between the North Pacific Central 

 Water and the North Pacific Equatorial Water was recently 

 completed. These waters are characterized by moderately 

 intense salinity and temperature gradients. On two cruises 

 (January-February and July, 1963) longline sets were made 

 in the transition zone area to the east of the Hawaiian Islands. 

 Ten traverses were made at longitude 150° W. between lati- 

 tudes 14° N. and 23° N. Catches of sharks and speartishes 

 tended to decrease as the longline stations progressed from 

 the low-salinity waters of the North Pacific Equatorial Water 

 through the transition zone and into the high-salinity water 

 of the North Pacific Central Water. Catches of lancetfish 



1950 1951 1952 1953 



1954 1955 1956 

 YEAR 



1957 1958 1959 1960 



Figure 14. — Regression of average number of men 

 hooking per effective trip on time (year), for 

 class 1 and class 2 vessels, 1950-60. Class 2 

 vessels are larger than class 1. 



( Alepisaurus ), however, increased in the high-salinity water. 

 During the first cruise the slender mola, Ranzania laevis 

 (Pennant), seemed to be the only fish definitely associated 

 with intermediate-salinity water. There was evidence that 

 this species was spawning. Also, on this cruise skipjack tuna 

 seemed to be associated with the predominantly North Equa- 

 torial Water while bigeye tuna catches were highest in the 

 high-salinity water (fig. 15). During the summer cruise, 

 however, catches of bigeye tuna were highest in the low-salin- 

 ity North Pacific Equatorial Water. 



During the first cruise from January to February we were 

 fortunate enough to observe the annual northward movement 

 of the salinity-temperature gradient (fig. 16). Heat-budget 

 computations showed little net heat exchange across the sea 

 surface during the cruise; therefore, the northward shift in 

 temperature and salinity must have resulted largely from 

 advective processes. 



