FISHERY BULLETIN: VOL. 75. NO. 4 



June 1974; however, one localized area did have 

 sharp, abrupt gradients. The eastward protruding 

 tongue of Transition Zone water centered at lat. 

 35°30'N, long. 132°30°W had salinity gradients 

 comparable with those found in previous years. 

 Substantial catches of albacore persisted in this 

 one region for a week after which fishing effort was 

 terminated. 



Further information on the distribution of alba- 

 core can be derived from the catches made by the 

 research vessels (Figure 10a-c). 10 The research 

 vessels trolled for albacore along tracks that 

 crossed the oceanic fronts and expended fishing 

 effort in Central, Subarctic, and Transition Zone 

 waters. With few exceptions, they did not catch 

 albacore in Central or Subarctic waters. In 1972 

 and again in 1973, when a large meander de- 



10 Catches are expressed in number offish caught per 15 line- 

 hours in 1972 and 1973 and per 60 line-hours in 1974. These 

 numbers of line-hours approximate the amount of fishing effort 

 expended each day by the research vessels during respective 

 years. 



veloped in the Subarctic front, albacore were 

 taken in the northward protrusion of Transition 

 Zone water (Figure 10a, b). Albacore often were 

 found close to the front. During each of the sur- 

 veys, catches were made by the research vessel as 

 the frontal gradients were being recorded by ship- 

 board instrumentation. 



Analyses of variance were performed upon the 

 charter vessel catch data to test the hypothesis 

 that catch rates were dependent upon water mass 

 in the offshore area during June. For the 1972 

 survey, daily or twice daily XBT casts were 

 matched with the daily catch data. Because 

 specific isotherms were found to fall within very 

 different depth ranges from one water mass to 

 another, the dependence of catch rate upon classes 

 of depth ranges for these isotherms was tested. 

 Thus for this statistical test the water masses may 

 be defined as follows: 



Water mass 

 Pacific Subarctic 

 Transition Zone 



Isotherm 

 58°F (14.4°C) 

 58°F 



Depth 

 <60 m 

 &60 m 



48' 



45 c 



150° 



145° 



140° 



135° 



130° 



-h" 



40° 



35° 



30' 



-TP^ 



45= 



40° 



55° 



51 ° 



25° 



125° 



150° 



140° 



135° 



130° 



120° 



FIGURE 10. — Albacore catch per 15 line-hours by National Marine Fisheries Service research vessel and 

 location of fronts delineating Transition Zone waters during: a. 4-23 June 1972; b. 9 June-5 July 1973; c. 29 

 May-1 July 1974. 



810 



