Bell, Robert R. 



The age composition of the California 

 Pacific albacore catch. /Conference 

 Paper VII -127 (See also Bell, Robert R. 

 196Z. Age determination of the Pacific 

 albacore of the California coast. Calif . 

 Fish and Game, vol. 48, no. 1, p. 39- 

 48.) 



Recent development of the scale method 

 for aging albacore by marine scientists of the 

 California State Fisheries Laboratory on Ter- 

 minal Island has made it possible to determine 

 the age composition of the catch and measure 

 year-class strength and fluctuations within- 

 creased precision. 



This paper reports on their preliminary 

 effort to determine the age composition of the 

 California commercial albacore catch. 



The age composition of the California 

 albacore catch for the last 3 months of the 1959 

 season was determined by sampling the catch 

 and aging the fish by the scale method. Scales 

 were selected from the area of the fifth dorsal 

 finlet. The checks found on these were believed 

 to be annual innatuie largely because of the good 

 correlation between them and the length fre- 

 quency modes found in the commercial catch. 



The smallest fish entering the California 

 catch (mean length for 1959 of 573 mm. ) had one 

 check and therefore were hypothesized to be fish 

 in their second year of life, most likely 16 to 18 

 months old. This hypothesis was also based on 

 the absence of a smaller mode either in the catch 

 or in survey collections. 



The majority of the fish appearing in the 

 second mode, the most important in the Califor- 

 nia fishery, had two checks on their scales. 

 These fish, believed to be in their third year of 

 life, had a mean length of 657 mm. 



The sample produced a class with a mean 

 length of 774 mm. for fish believed to be in the 

 fourth year of life, and two other age groups, 

 those in the fifth and sixth year of life having 

 mean lengths of 837 and 878 mm. , respectively. 



The California tagging studies have since 

 verified assumptions that the length frequency 

 modes are 1 year apart in age. Tagging studies 

 have also verified the growth determined by the 

 scale aging method. 



The California commercial albacore 

 catch in the last 3 months of the 1959 season 

 (September-November) amounted to 13, 978, 766 



pounds. The catch in numbers was computed to 

 be 934,297 fish. Fish of age group II were found 

 to comprise 58 percent of the catch. Fifty-five 

 percent of the catch was supported by fishfrom 

 63 to 68 cm. in fork length. This is the second 

 mode in the commercial catch and composed of 

 86 percent age group II fish, 11 percent age group 

 I fish, and 3 percent age group III fish. 



Blackburn, Maurice 



Distribution and abundance of Eastern 

 Tropical Pacific tunas in relation to 

 ocean properties and features. //Con- 

 ference Paper V - \J 



The coastal waters from southern Cali- 

 fornia to northern Chile were divided into 16 

 areas, 5 of which included offshore islands or 

 island groups. In explaining the generally high 

 abundance of skipjack and yellowfin in this re- 

 gion of complex oceanographic conditions, the 

 following generalizations about the region are 

 made: 



1. Temperatures in surface waters are 

 generally > 21° C. (70° F. ) in the fishing 

 seasons. 



2. Winds result in upwelling and enrich- 

 ment in certain areas and a shoaling of the ther- 

 mocline in the region as a whole. 



3. Winds over very shoal thermo- 

 clines result in localized vertical mixing and 

 enrichment. 



4. Seasonal changes are minimal; thus 

 favorable conditions for tuna aggregations may 

 persist for several months. 



The 16 areas may be grouped loosely in 

 three general categories: 



(1) The extremes of the region: areas 

 north of 22° N. and south of 5°S. Seasonal var- 

 iations in distribution of yellowfin and skipjack 

 tuna are rather pronounced and correspond to 

 the seasonal march of surface isotherms, par- 

 ticularly 21° C. in the northern areas. During 

 years in which the warm waters are found in 

 more northerly and southerly latitudes , tuna are 

 also found in more northerly and southerly areas. 

 Some areas are biologically productive because 

 of upwelling. 



(2) The center of t h e region: coastal 

 areas from southern Mexico to Ecuador (22° N. 

 to 5° S. ). Surface temperatures are almost al- 

 ways > 21° C. Thermoclines are shoal in most 

 areas. Tuna (yellowfin and/or skipjack) occur 

 in most areas at most seasons. Skipjack may 

 be excluded from areas of surface temperatures 

 above 28° C. (83° F. ). Seasonal variations in 

 tuna abundance and ocean properties are smaller 



