FISHERY BULLETIN: VOL. 75. NO. 4 



The last two charts in this series (Figure 6d, e, 

 through the end of July 1973) reveal subsequent 

 stages of albacore migration and commencement 

 of the nearshore fishery. The relative abundance 

 of albacore was high in nearshore waters by late 

 July. In comparison to recent years, the 1973 

 nearshore fishery started about 3 weeks late. 



SIZE COMPOSITION OF FISH 



TABLE 2. — Percentage size composition by number and by weight 

 for albacore catches made by American Fishermen's Research 

 Foundation charter vessels in the offshore area west of long. 

 130°W and south of lat. 38°N. 



'Estimated from length-weight relationship given by Clemens (1961). 



Three size modal groups of fish were caught in 

 each year by the AFRF charter vessels; however, 

 the relative proportions of the size groups varied 

 among the years (Figure 7; Table 2). In 1972 about 

 equal proportions of each size modal group were 

 caught. In 1973 and 1974 the medium-size modal 



AFRF CHARTER, 1972 

 TOTAL =6,428 ALBACORE 



45 50 55 60 65 70 75 



i i i i i i i i 

 85 90 95 100 



FORK LENGTH IN CENTIMETERS 



FIGURE 

 sus fork 

 surveys 



806 



i > i — i — i — i — i — i — i — i — i — i — i — i — i — i i i 



z 3 4 5 6 7 8 9 10 12 14 16 18 20 



WEIGHT IN KILOGRAMS 



7. — Size composition by percent frequency of catch ver- 

 length for total catches of albacore from the research 

 in 1972-74. 



group was predominant and the larger one nearly 

 absent. 



THE MARINE ENVIRONMENT 



Albacore were found mainly in Transition Zone 

 waters. Variations in distribution and relative 

 abundance between each of the surveys appeared 

 to be related to oceanographic conditions of the 

 Transition Zone. Transition Zone waters lie be- 

 tween the cool low salinity Pacific Subarctic wa- 

 ters to the north and the warm, saline Eastern 

 North Pacific Central waters to the south and have 

 temperatures and salinities that are characteris- 

 tic of a mixture of these two primary water masses 

 (Sverdrup et al. 1942; Christensen and Lee 1965). 

 Transition Zone waters are found in a band across 

 the North Pacific middle latitudes within the 

 North Pacific Current and are bounded by sharp 

 horizontal gradients in temperature and salinity 

 (McGary and Stroup 1956; Roden 1970, 1972, 

 1975). These bounding gradient regions are some- 

 times referred to as the Subtropic and Subarctic 

 fronts. The dynamic processes which produce and 

 maintain these gradients also enrich these waters 

 (McGary and Stroup 1956). 



An oceanographic section of the vertical dis- 

 tribution of temperature and salinity was taken 

 along long. 137°30'W in June 1972, 1973, and 

 1974 (Figure 8). In 1972 and 1973, Subarctic wa- 

 ters were found north of lat. 35 °N and Central 

 waters south of lat. 31°30'N and 32 °N, respec- 

 tively. Boundaries of the Transition Zone between 

 these water masses were well developed and read- 

 ily identifiable. The Subarctic front was marked 

 by abrupt shoaling of the 33.8%o isohaline and 

 58°F (14.4°C) isotherm and a sharp horizontal 

 gradient in salinity extending from the surface to 

 greater than 175 m. The Subtropic front was de- 

 lineated by steep shoaling of the 34.2%o isohaline 

 and 62°F ( 16.7°C) isotherm and a sharp gradient in 

 salinity extending from the surface to greater 



