the central west coast of Baja California were ob- 

 tained from half-month average sea surface 

 isotherm charts published by the National Marine 

 Fisheries Service (U. S. Bureau of Commercial 

 Fisheries, 1961). These isotherm charts are com- 

 puted from sea surface temperatures reported by 

 ships in the eastern Pacific. From examination of 

 these isotherm charts temperatures off San Diego 

 and to the south toward central Baja California 

 were highest during the fishing seasons of 1963 and 

 1967, and lowest during the 1965 season (catches of 

 1,410, 602, and 296 respectively). 



Of particular interest to fishermen is the time of 

 the beginning of the fishing season. Early in the 

 fishing season off San Diego during the period prior 

 to an increase in sea surface temperature to 68° F 

 (20.0°C) the total number of marlin caught was 115, 

 2.5% of the total catch of 4,535 fishes (1963-1970), 

 whereas for the first half-month period of each year 

 showing the 68° F (20.0° C) isotherm off San Diego, 

 the catch totaled 824 fish, representing an increase 

 to 18.2% of the total catch. 



During the half-month periods, data show that 

 temperatures were below 68°F (20.0° C) for 23 

 periods, and during this time a total of 931 fish, or 

 an average of 40.5 fish/period, were caught. Tem- 

 peratures were between 68° F (20.0° C) and 69.9° F 

 (21.0° C) during 15 periods, and 1,886 fish were 

 caught, resulting in an average catch of 99.2 

 fish/period. Temperatures of 70° F (21.0° C) or 

 above for 14 periods resulted in a catch of 1,718 fish 

 or an average catch of 122.7/period. 



The numbers of marlin caught during the half- 

 month periods when the 68° F (20.0° C) and 70° F 

 (21.0° C) isotherms were continuous from off Baja 

 California northward to off southern California 

 were compared to the catch when these isotherms 

 were discontinuous (Table 3). For examples of con- 

 tinuous and discontinuous isotherms in the area of 

 study, see Figure 7. 



Data show that during periods when the 68° F 

 (20.0° C) or 70° F (21.1° C) average isotherms were 

 continuous from off central Baja California north- 

 ward to off southern California, a total of 2,046 fish 

 was caught for an average catch/period of 146.1 

 fish, whereas a total of 1,599 fish was caught for an 

 average catch of 82.0/period when these isotherms 

 were discontinuous. During periods when the 70° F 

 (21.1° C) average isotherm was continuous the 

 largest catch per any period (570 fish) and the high- 

 est average catch rate/period (205.3 fish) was re- 

 corded. 



Table 3. — Comparison of catch and catch rates during 

 periods of continuous and discontinuous 68° (20.0°C) and 

 70° F (2 l.rC) isotherms. 



(20.0°C) 



70°F 

 21, rc) 



Totals 



Figure 7. — Examples of discontinuous isotherms (7a) and 

 continuous isotherms (7b) in the area of study. 



From examination of the temperature structure 

 of the waters off northern Baja California and 

 southern California based on half-month average 

 temperature charts it appears that 1) initial warming 

 of the waters to an average temperature of 68° F 

 (20.0° C) is related to an increase in catch, 2) con- 

 tinuity of the 68° F (20.0° C) or 70° F (21.1° C) 

 average isotherms from off central Baja California 

 northward to off southern California was associated 

 with higher catches compared to catches when 

 these isotherms were discontinuous. 



LITERATURE CITED 



CLEMENS, H. B.. and W. L. CRAIG. 



1965. An analysis of California's albacore fishery. Calif. 

 Dep. Fish Game. Fish. BuU. 128, 301 p. 

 HESTER, F. J. 



1961. A method of predicting tuna catch by using coastal 

 sea-surface temperatures. Calif. Fish Game 47:313-326. 



192 



