along current boundaries, and in certain areas 

 near islands, sea mounts, and along continental 

 slopes. Each of these features may contribute 

 to enrichment of the surface waters. Although 

 temperature is a good indicator of each of these 

 features, it may not be the main factor directing 

 the behavior and distribution of tuna. Changes 

 in the environmental factors in the sea are the 

 result of interaction between the sea and atmos- 

 phere, and thus a correlation between meteoro- 

 logical factors and behavior of the tunas can be 

 found. A discussion of tuna fishing grounds and 

 methods is included. 



Royce, William F. 



A morphometric study of yellowfin tuna 

 Thunnus a 1 b a c a r e s (Bonnaterre). 

 /"Conference Paper III - b] (In press 

 as U. S. Fish and Wildlife Service 

 Fishery Bulletin, number unknown) 



Morphometric measurements are com- 

 paredfrom 4,180 yellowfin tuna from 29 locations 

 in the Pacific Ocean, from the Atlantic Ocean 

 off Angola, Africa, and from the Indian Ocean 

 off Somaliland, Africa. The measurements used 

 are head length, pectoral fin length, second dor- 

 sal fin height, anal fin height, snout to insertion 

 of first dorsal fin, snout to insertion of second 

 dorsal fin, snout to insertion of anal fin, snout 

 to insertion ofventral fin, insertion ofventral to 

 anterior edge of vent, and greatest body depth. 

 Each measurement is related to fork length by 

 regression analysis, and each relationship is 

 called a character. Curvilinear regression due 

 to allometric growth is controlled bytransform- 

 ing some data to logarithms and by separating 

 all samples into small, medium, and large size 

 groups (< 80, 80-120, and > 120 cm. fork length , 

 respectively). Mean character sizes are deter - 

 mined for each sample at lengths of 65 cm. , 100 

 cm. , and 140 cm. 



A comparison of mean character sizes 

 from samples taken along the Pacific Equator 

 reveals a cline in most characters between the 

 vicinity of Costa Rica and the Caroline Islands. 

 The yellowfin from the eastern Pacific have 

 larger heads and greater distances from the 

 snout to the insertion of first dorsal, second 

 dorsal, ventral, and anal fins, a greater dis- 

 tance from insertion of ventral to insertion of 

 anal fin, and a greater body depth. On the other 

 hand they have shorter pectoral fins and much 

 shorter anal and second dorsal fins. The sam- 

 ples from the more temperate parts of the Pacific 

 and from off the coasts of Africa differ little 

 from some part of this cline. 



A multiple character comparison of over- 

 lap among samples from near the Pacific Equa- 



tor shows less than 50 percent overlap between 

 samples separated by 1, 500 miles, less than 25 

 percent overlap between samples separated by 

 3, 000 miles and less than 6 percent overlap be- 

 tween samples separated by 6, 000 miles. The 

 possibility of long intermigrations among the 

 equatorial stocks seems remote. 



The full variation in length of pectoral 

 and heights of second dorsal and anal fins, which 

 most authors have used to separate the species 

 of yellowfin, occurs within the cline along the 

 Pacific Equator. This occurrence plus the con- 

 tinuous circumtropical high seas distribution of 

 the yellowfin indicates a single worldwide spe- 

 cies. The appropriate name is Thunnus alba- 

 cares (Bonnaterre) 1788. 



Seckel, Gunter R. , and Thomas S. Austin 



The association between Hawaiian skip- 

 jack landings and the oceanographic 

 climate. /Conference Paper V - 10_/ 



In an effort to relate the seasonal and 

 annual availability of Hawaiian skipjack to fac- 

 tors in their environment, it was found that the 

 season catch could be correlated with the per- 

 centage occurrence of northeast trades during 

 February through April for a number of years. 

 This correlation later failed. In the Hawaiian 

 Islands, low summer salinities (less than35 %a) 

 were also associated, although not without excep- 

 tions, with better than average annual landings. 

 Plotting the monthly rate of change of surface 

 temperature obtained at Koko Head, Oa h u, 

 against time, one obtains a heating curve with a 

 shape characteristic of the locality. Occurrence 

 of initial heating during February was followed 

 by an average or better than average fishing 

 season and initial heating during March by a 

 poorer than average season. This correlation, 

 which has held for the 10 years for which data 

 are available, is of predictive value. 



In terms of environmental processes, 

 initial warming of the heating curve signifies the 

 beginning of the northward movement of the 

 boundary between the high salinity North Pacific 

 Central water and the lower salinity California 

 Current Extension water. Later, the boundary, 

 which during autumn and winter months lies just 

 south of the islands, moves into the island area 

 and accounts for the lower summer salinities. 

 Early northward movement of the boundary as 

 reflected by initial warming at Koko Head signi- 

 fies a well-developed circulation. 



The 10-year Koko Head heating curve and 

 monthly skipjack landings show that catches 



