LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA 



150° 145° 140° 135" 130° 



)H 



45° - 



1 — r 



40= 



35° 



30° 



25' 



MAY29-JUNE30, 1974 



CATCH/150 LINE HOURS 

 x No Catch 





' f 



> * a 



V A 



J I I L- 



_ 



_L 



25° 



150° 145° 140° 135° 130° 125° 



FIGURE 4. — Albacore catch per 150 line-hours by American Fishermen's Research Foundation charter vessels: 

 a. 23 May-10 July 1972; b. 10 May-16 July 1973; c. 29 May-30 June 1974. 



the offshore area of high catches and inshore wa- 

 ters. 



Differences Within Surveys 



Representative information on spatial and tem- 

 poral variations in the distribution and relative 

 abundance of albacore in offshore waters during 

 May and June is given in Figure 5a-e. In the early 

 part of the 1973 survey, 10 to 30 May, four vessels 

 worked westward making only small scattered 

 catches between lat. 31° and 35°N, long. 142° and 

 145°W. In the second time period, 31 May to 9 

 June, the vessels returned through waters they 

 had scouted earlier and began making catches of 

 over 100 fish/day between lat. 32° and 34°N, long. 

 139° and 143°W. Good catches continued to be 

 made in the general area of lat. 33° to 35°N, long. 

 135° to 143°W for several weeks with charter ves- 

 sels landing up to 300 fish/day on many days. A 

 second group of four charter boats, which left San 

 Diego on 25 May, did not catch any fish until 4 



June when they moved westward of long. 139°W 

 near lat. 33° to 35°N. On their return to San Diego 

 during mid- June, the first group of boats failed to 

 catch any fish east of long. 135°W despite favora- 

 ble ocean temperature conditions. Similarly, on 

 the return to San Diego near the end of June, 

 catches by the second group of charter boats drop- 

 ped off abruptly east of long. 135°W with only 

 small scattered or no catches made east of Fieber- 

 ling Guyot (long. 128°W). The four vessels survey- 

 ing the area north of lat. 38°N found generally 

 poor to moderate catches. (The region lat. 35° to 

 38°N was not covered by the fishing vessels.) This 

 sequence of catch charts shows that: 1 ) albacore 

 were apparently unavailable to jig fishing, except 

 for scattered catches, through May in a region 

 which subsequently was to prove very productive; 

 2) albacore became available to trolling gear in the 

 first week of June in a region which will be shown 

 later to be associated with the subtropic boundary 

 of the Transition Zone; 3) good catches persisted 

 within a block of 2° latitude by 7° longitude for 



801 



