SQUIRE: PELAGIC MARINE FISHES OFF SOUTHERN AND CENTRAL CALIFORNIA 



Table 5. — Average weight per school (data from Sep- 

 tember 1962 through December 1966). 



Species 



Northern anchovy 

 Pacific sardine 

 Jack mackerel 

 Skipjack tuna 

 Albacore 

 Bluefin tuna 

 Pacific bonito 

 Pacific mackerel 

 Yellowtail 

 White seabass 

 Pacific barracuda 



= Avg. tons/school 



184 



index formula. Midpoints were not reduced for 

 Pacific barracuda and yellowtail. Range of ob- 

 served tonnage and X values are shown in Table 

 6. 



The following formula was used to calculate 

 annual indexes of apparent abundance, day and 

 night, for each species by zone and the day/night 

 index of annual average apparent abundance for 

 each species. 



Index of apparent abundance 



= ^ NiXi + N2X2 + N3X3 + N4X4 



Nt 



where: N1.2.3A — number of block area flights 



in which the species oc- 

 curred at value Zi,2.3,4. 



Xi,2,3,4 — tonnage range values. 



Nt — total number of block area 

 flights in the zone during 

 the year. 



Day and night indexes of apparent abundance 

 for each zone and the annual average day/night 

 indexes of apparent abundance for all zones are 

 listed in Table 7. 



DISCUSSION AND SUMMARY 



A direct, precise measure of total abundance 

 is most desirable for the management of pelagic 

 marine species. However, at the present time 

 and into the foreseeable future, this degree of 

 accuracy in the measurement of total abundance 

 cannot be attained. Therefore, pelagic resource 

 mangement will be required to rely on an indirect 

 measure of total abundance. Some observations 

 on the relation between the index of apparent 

 abundance and changes in estimates of total 

 abundance can be made. For the years 1963 

 through 1969, either separately or combined, 

 some data are available giving estimates of total 

 abundance, spawning biomass, or indexes of 

 abundance for such species as the northern an- 

 chovy. Pacific mackerel. Pacific sardine, jack 

 mackerel, and Pacific bonito. However, all such 

 estimates were calculated from data obtained 

 from such measures as catch, eff"ort, catch com- 

 position, fecundity, and egg and larval counts. 

 No direct measurements of total abundance were 



Table 6. — Range of tonnage and tonnage range values 



(X). 



1013 



