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Figure 15.— Catch and temperature data by block area for white seabass 

 caught off southern California. 



Along the coast south of the United States-Mexico border, the 

 northern boundary of an extensive coastal upwelling zone is fre- 

 quently observed. The upwelling increases along the shore to the 

 south and often extends further offshore. Temperatures warmer than 

 those found near the coast of Mexico occur offshore about the Cor- 

 onado Islands (block 916); these temperatures are more typical of 

 those found nearshore off Point La Jolla in the northern portion of the 

 survey area. 



The 3-yr survey period off San Diego showed that 1973 was cooler 

 than 1972, which was a year with above-normal warming along the 

 west coast of North and South America ("El Nino" year). The aver- 



age temperatures in 1974 were warmer than those in 1973, but not as 

 warm as those in 1972. In 1974, however, an anomalous short-term 

 warming period occurred in early July off southern California, and 

 the highest temperatures for the 3-yr period were recorded at that 

 time. 



Species of yellowtail, Pacific barracuda, and Pacific bonito were 

 selected for study, since statewide maximum catches of these three 

 species were recorded in 1963-68 surveys from block areas within 

 the study area. These blocks gave the greatest catch sample, and if a 

 relation between catch and temperature exists it may be evident in the 

 data for these block areas. 



The temperatures obtained during the surveys, catch in numbers of 

 fish , and the CPUE are given by weeks in 1 972-74 for species of yel- 

 lowtail (block 916), Pacific bonito (block 860), and Pacific barra- 

 cuda (block 860) in Figure 21, 22, 23 a, b, c. 



Catch Temperature Variation 



There is considerable variation in catch temperature relative to the 

 geographical location of the temperature measurements. The 

 1963-68 observations of yellowtail are one example: in the leading 

 block area near the Coronado Islands (block 916), the mean catch 

 temperature was 17.5°C (63.6°F), while 20 mi away off the Point La 

 Jolla-Pacific Beach area (block 860) it was 17.9°C (64.2°F). Far- 

 ther north about Catalina Island (block 761), it was 17.4°C (63.4°F), 

 similar to that of the Coronado Islands. However, 30 mi north of 

 Catalina Island along the mainland coast off Point Vincente (block 

 720), the mean catch temperature rose to 19.0°C (66.2°F). 



Although catch temperature data are limited for the sport catch of 

 albacore off southern California, catch temperatures west of San 

 Diego averaged 18.3°C (65°F) to 18.9°C (66°F). Airborne temper- 

 ature surveys off central California observed that commercial alba- 

 core fishing operations were in waters of 16. 1 °C (61 .0°F) to 17.2°C 

 (63.0°F) (Squire 1969). 



By using the block areas containing major catch as "key areas" for 

 the pelagic species of interest, it is reasonable to assume that temper- 

 ature and catch data could be used within statistical limits to better 

 define the relation of environment to catch. The 1972-74 surveys 

 were conducted for this purpose and a detailed anaylsis made of the 

 catch, temperature, and effort data. 



ANALYSIS AND CONCLUSIONS- 

 PARTS I AND n 



In natural populations where sampling is selective rather than ran- 

 dom or systematic, it is extremely difficult to separate chance events 

 from fundamental or persistent relationships. This is particularly true 

 of catch-environmental relationships because 1) all organisms seem 

 to aggregate in time and space, 2) the nature of the selectivity (non- 

 randomness of effort) is itself environmentally related, and 3) spatial- 

 temporal-environmental interactions may completely obscure the 

 main effects. 



It is common for fisheries researchers to attempt to establish a rela- 

 tionship between catch and temperature. In a study of this type, the 

 important considerations are that 1) temperature is seasonally cycli- 

 cal and monotonically increases or decreases within season, and 2) 

 spatial-environmental interactions will alter the probabilites that the 

 population will be within the range of the fishing gear Thus, in order 

 to establish evidence for temperature preference, one must, at mini- 

 mum, stratify catch by season and area, and examine the relationship 

 of temperature and catch or CPUE within strata. The limitation of 

 this kind of analysis is that, within strata, the temperature range is 



11 



