Squire Aerial monitoring of abundance of pelagic fishes 



351 



are thus not directly comparable to other years, al- 

 though most search effort was during a period of high 

 abundance levels. Through the years, the center of 

 search effort was off southern California, with search 

 activity off northwestern Baja California, Mexico dur- 



ing the summer for bluefin tuna. There was consider- 

 able search effort north of Point Conception into the 

 Monterey Bay area for chub mackerel and Pacific sar- 

 dine during the early years of the program and less so 

 since the decline in those species' abundances in the 

 mid-1960s. 



Estimates of total tonnage sighted by species by zone 

 are given in Table 2. The tonnage estimated for north- 

 ern anchovy far exceeds that of all other species, total- 

 ing 89.7%. The greatest tonnage of northern anchovy 

 was observed in zone G; Pacific sardine, Pacific bonito, 

 and chub mackerel in zone C; jack mackerel in zone F; 

 and bluefin tuna in zone N. 



Most spotting effort was carried out during summer 

 to fall, with 49% of BAFs accounted for during the 

 months of July, August, and September ( 1980-90). Dur- 

 ing any one year, the amount of effort expended in any 

 one month was highly variable due to fluctuations in 

 abundance, weather, and fleet operations. In summer 

 months, a substantial portion of the increase in spot- 

 ting effort is related to searching for bluefin tuna, or 

 other species such as albacore Thunnus alalunga and 

 yellowfin tuna Thunnus albacares. 



Differences in tonnage sighted between day and night 

 (Table 3) are similar to that reported by Squire ( 1972). 

 Northern anchovy, Pacific sardine, chub mackerel, and 

 jack mackerel were more commonly observed at night, 

 while Pacific bonito and bluefin tuna were more com- 

 monly observed during the day. 



