400 



54" 



55^ 



56" 



/Jater Temperature °F. 

 57° 58° 59° 



60" 



61" 



62" 



63° 



360 



320 



280 



240 



200 



160 



120 



Parsed on 1011 tuna taken by the Cobb 

 from June to Seoteraber, 1950 



FIGURE 29 - ALBACORE CATCHES IN RELATION TO SURFACE WATER TEMPERATURES. 



The progressive northward movement of the zohe of warmer water as delineated by the 

 57.5 F. surface isotherm through the months of June, July, and August (see fig, 2) 

 determines to a great extent the time of appearance and the inshore northerly mi- 

 gration of tuna in the waters of the northeastern Pacific. 



An examination of figures 30 to 35 will show the northeasterly progres- 

 sion of the zone of warmer surface water through the late spring and summer months 

 of 1950 and its relation to tuna catches by the Cobb . It will be noted that the 

 58° isotherm reached the area off the Columbia River sometime in the early part 

 of July, which coincides closely with the usual arrival of albacore in quantities 

 in this region. These isothermic trends tend to follow a similar pattern annually, 

 and early or late arrival of albacore adong the Oregon and Washington coasts will 

 probably closely coincide with the appearance of warm water in the offshore re- 

 gions. Note that in only one instance through this phase of the cruise, June 12 

 through July 26, were tuna caught in waters below 57° F. The first tuna taken by 

 the John N. Cobb . June 18, were caught shortly after the vessel reached water of 

 57.5° F. Tsee fig, 30). The Cobb trolled southwesterly from Cape Flattery, Wash- 

 ington, and no fish were taken until the warmer water was reached off Cape Blanco, 

 Ore. Continued trolling in colder waters to the east and north of this warm water 

 produced no fish. Fishing activity throughout the summer was by no means confined 

 to the so-called warm "tuna water," and much time was spent fishing the colder ad- 

 jacent waters, with only a few scattered fish being taken. 



A graph representing water temperatures in relation to tuna catches (see 

 fig. 29) shows that the majority of the albacore were caught in the temperature 

 range of 58° to 60° F. Although fish were taken in waters from 54° to 62° F,, the 



37 



