SAL DISTRIBUTION CF 



The depth at which the deep-swim- mas are most abundant 



is of considerable interest biologically and of practical importance 

 commercially. It has been previously noted ( ikamura 19h3 s 



Cchi 19 52, and Murphy and Shomura 1953) that in gen 



;eye tun in greater numbers on the lowermost hooks of 



the Ion Line, 



In the absence oJ -•mation or .ctual dep' apture, 



the catches can be examined for catch rates at three relative depth 



vels (shallow, intermediate, and deer 'amination of the catches 



of yellowfin and bigeye tuna by relative depth of capture for Manning 

 Cruise 11 (tables 11 and 12) show that the deeper- fishing hooks usually 



jher c;. than the shallow hooks Eoth chi-square analyses, 



however, show si i :ant interaction chi-square which indicates 

 that the p, on the deep hooks was not consistent, 



'icantlj ■ vellowfin were taken on the shallow hooks at 



stations ?, ?3, and 2U (table 11) „ Trie bigeye data (table 12) show 

 reversal in the relationship of the intermediate and deep hooks „ 

 may well be ; tion of the line 



to critical isotherms or the thermocline is different 

 from <' r to itation Tbj di I ition of the albacore catch- 



(table 13' >od evidence that this species occupies the deeper, 



cooler ' i of water in the tropics <> 



depth data fr ;e 1 ( tabl and 15) 



indi ■ * h n those se on 120° and 130° VT. longitude were 



hed, the yellowfin were not stratified with depth so far as the 

 dep + ; • fished by our gear is concerned. Ihe bigeye, on the. 



other hand, gave evidence of being more abundant at the levels 

 fished by the deep hooks „ The failure of the deep hooks to c? 



3 yellowfin may be a function of the shall w 1 

 experienced d r this f j ' (fig« h)» These shallow thermoclines, 



with the possible attendant streaming of the line, m iced 



all of the hooks at more nearly the same level than e the 



yellowfin are the least markedly stratified w it might be 



■ ed that if the differential between shs were 



small, difference would be no- hes at ' : 



three relative depth levels„ 



In an attei ) ascertain the actual depth of the main line 



a depth indicator was attached to the base of one of the central or 



ans during Cruise 11 of ' .., gauge 



was designed to furnish an estimate of the deepest point reached by 

 the portion of the line to which the instrument was attached. The 

 correlation of the depths indicated by the ' ^pth of 



the top of the thermocline (table 16) is Co'' P <0„05, suggesting 

 that under some cj "ances the the Lne limits the penet 



result n be expected at least part of the time 



the thermocline is the boundary between moving surface water and 

 the relatively still deeper layers „ 



19 



