APPARENT ABUNDANCE OF SOME PELAGIC MARINE FISHES OFF 



THE SOUTHERN AND CENTRAL CALIFORNIA COAST AS SURVEYED 



BY AN AIRBORNE MONITORING PROGRAM 



James L. Squire, Jr.^ 



ABSTRACT 



From September 1962 through December 1969, commercial aerial fish spotter pilots esti- 

 mated tonnage of species observed during flights off the southern and central California 

 coast. Observations of fish and the aircraft's flight route were recorded on special charts. 

 These data were analyzed using 10-minute-longitude by 10-minute-latitude "block areas." 

 A total of over 17,593 flight hours was involved, surveying 57,628 block areas — 37,186 

 during the day and 20,442 during the night. Data from each block area were used to 

 compute diurnal and nocturnal variation in apparent abundance and an annual index 

 of apparent abundance. 



Pacific bonito, Sarda chiliensis, and yellowtail, Seriola dorsalis, were observed in greater 

 frequency and quantity during the day, and the northern anchovy, Engraulis mordax; 

 jack mackerel, Trachiirus symmetriciis \ and Pacific mackerel. Scomber japoniais, were 

 observed in greater frequency and quantity during the night. Pacific barracuda, Sphy- 

 raena argentea, was observed in greater quantity at night but more frequently during 

 the day. 



Between 1963 and 1969 indexes of apparent abundance declined for jack mackerel. 

 Pacific mackerel, Pacific sardine. Pacific bonito, Pacific barracuda, and yellowtail and 

 increased slightly for the northern anchovy. The index closely follows estimates of 

 total abundance for the Pacific mackerel, a species for which reliable estimates of total 

 abundance are available. From observations of the catch trends in the bonito fishery, 

 the index appears to be little aff'ected by changes in economic demand. Its trends in 

 apparent abundance are evident before they are reflected in catches and are useful in 

 the evaluation of catch variations in underutilized resources. 



In a search for more efficient fishing methods, 

 many of the fisheries throughout the world that 

 catch pelagic surface schooling species are using 

 aircraft to locate and guide the fleet to the schools 

 and in some cases to direct the catching oper- 

 ation (Gushing, Devoid, Marr, and Kristjonsson, 

 1952). In some areas of the United States the 

 services of the fish spotter are vital to the suc- 

 cess of the commercial fleet which depends in 

 part on the aircraft scouting the fishing grounds 

 to obtain current information on the location of 

 near-surface schooling fish (Squire, 1961), At 

 times commercial aerial fish spotters assist the 



* National Marine Fisheries Service, Southwest Fish- 

 eries Center, La Jolla. CA 92057, 



Manuscript accepted March 1972. 

 FISHERY BULLETIN: VOL. 70, NO. 3, 



1972. 



sport fishing fleet by advising them of the lo- 

 cation of desirable marine game species. 



Data obtainable by techniques of aerial obser- 

 vation have been used by fishery biologists to 

 gain information on distribution and abundance 

 of pelagic near-surface schooling fish, 



Sette (1949) investigated the possibilities of 

 aerial scouting for sardines off southern Cali- 

 fornia in search of a method that would provide 

 information useful in estimating abundance yet 

 be free of the availability influence. Aerial 

 scouting was conducted during the day, and com- 

 mercial fishing was conducted at night. As a 

 result the spotting data were deemed less reli- 

 able than those obtained from the commercial 

 fishery. 



Jones and Sund (1967), using commercial fish 



1005 



