Abstract. -During the period 

 1962-90, an aerial monitoring pro- 

 gram conducted in cooperation with 

 aerial spotters searching for pelagic 

 fishes off California and Baja Califor- 

 nia, Mexico resulted in the develop- 

 ment of an index of apparent abun- 

 dance for six species of fishes: the 

 northern anchovy Engraulis mordax, 

 Pacific sardine Sardinops sagax, Pa- 

 cific bonito Sarda chiliensis. Chub 

 mackerel Scomber japonicus, jack 

 mackerel Trachurus symmetricus, and 

 bluefin tuna Thunnus thynnus. North- 

 ern anchovy was the dominant spe- 

 cies observed, accounting for 89.7% of 

 tonnage recorded during 1962-90. 

 Chub mackerel comprised 6.1% of the 

 total tonnage, jack mackerel 2.1%, Pa- 

 cific sardine 1.0%, Pacific bonito 0.6%, 

 and bluefin tuna 0.5%. 

 Apparent abundance indices were 

 computed by dividing the tonnage ob- 

 served by the number of "block areas" 

 (10' lat. x 10" long.) searched, ex- 

 pressed as tons/block area flown (T/ 

 BAF). Indices were calculated for the 

 total area and for the core area of dis- 

 tribution and abundance for each spe- 

 cies. All species exhibited large 

 fluctuations in apparent abundance 

 over time. The apparent abundance 

 index for Pacific sardine declined to a 

 very low level during 1966-83. A sub- 

 stantial increase in abundance oc- 

 curred during the mid- to late-1980s, 

 with the 1990 index value 58 times 

 that observed during the early 1960s. 

 The chub mackerel abundance index 

 declined to a very low level during 

 1966-76, then increased to a record 

 high value in 1978 and has since de- 

 clined. The northern anchovy abun- 

 dance index increased in the early 

 1970s, with high abundance levels re- 

 corded during 1972-81, and then de- 

 clined sharply to very low levels in the 

 1980s. The Pacific bonito abundance 

 index was high during 1965-67 and 

 1983-85, with current levels well be- 

 low the long-term mean. Very high 

 abundance index levels for jack mack- 

 erel were recorded during 1975-79, 

 then declining to very low levels in the 

 1980s. The bluefin tuna abundance in- 

 dex increased during 1972-80, declin- 

 ing to very low index values since. 

 Based on these data, several species 

 appear to be fluctuating unpredictably 

 with respect to species abundance over 

 time. 



Aerial indices were compared with 

 available total, spawning, and larval 

 biomass estimates developed for sev- 

 eral species. The most significant cor- 

 relation of the aerial index was be- 

 tween the northern anchovy and 

 Pacific sardine larval indices. 



348 



Relative abundance of pelagic 

 resources utilized by the California 

 purse-seine fishery: Results of an 

 airborne monitoring program, 

 1962-90 



James L. Squire, Jr. 



Southwest Fisheries Science Center 



National Marine Fisheries Service. NOAA 



8604 La Jolla Shores Drive, La Jolla, California 92038 



The rapid decline of the Pacific sar- 

 dine Sardinops sagax fishery in the 

 late 1940s resulted in increased re- 

 search by the State of California 

 Department of Fish and Game 

 (CDF&G), Federal Government, and 

 other institutions to determine the 

 underlying principles that govern 

 the sardine's behavior, availability 

 to the fishery, and total abundance 

 (Clark & Marr 1955, Sette 1969, 

 Radovich 1982). Catch-per-unit-effort 

 (CPUE) studies of the sardine purse- 

 seine fishery off California did not 

 indicate a significant decline in 

 abundance until just prior to the 

 fishery collapse (Fox 1974). Fisher- 

 ies tend to target their fishing effort 

 in areas of high densities of fishes 

 (Radovich 1982, Squire & Au 1990), 

 hence CPUE may not accurately re- 

 flect resource abundance (de La 

 Mare 1984; J.B. Phillips, CDF&G, 

 pers. commun., 1954). Clark & Marr 

 ( 1955) concluded that, in addition to 

 other information needs, better in- 

 formation is needed on changes in 

 availability of sardine to the fishery. 

 Related to this is the need for better 

 real-time measures of trends in ap- 

 parent abundance for successful 

 management of pelagic schooling re- 

 sources. 



In the mid-1950s, the use of air- 

 craft in searching and fishing opera- 



Manuscript accepted 28 January 1993. 

 Fishery Bulletin, U.S. 93:348-361 ( 1993). 



tions of the California purse-seine 

 fleet had become well established, as 

 was the case in many other U.S. 

 fisheries (Squire 1961). Having had 

 experience in conducting commercial 

 aerial fish spotting and several aerial 

 fish-resource surveys, I initiated a pe- 

 lagic monitoring program in the fall 

 of 1962, with the cooperation of aerial 

 fish-spotter pilots searching for fish 

 for the commercial purse-seine 

 fishery off central and southern Cali- 

 fornia. The purpose of the program 

 was to develop an effective method 

 of measuring apparent abundance 

 and monitoring changes in abun- 

 dance. In the case of aerial observa- 

 tions, the concentrations of fish ob- 

 served may or may not be subjected 

 to fishing. 



This paper updates the analysis 

 of apparent abundance data col- 

 lected by the aerial monitoring pro- 

 gram from the first full year of data, 

 1963-90, using different analytical 

 methods than used in earlier papers 

 (Squire 1972, 1983). It also reviews 

 the trends in apparent abundance 

 during the period 1963-90 for six 

 pelagic species by geographical area 

 and compares the relation of the 

 aerial abundance estimates to other 

 independent biomass estimates 

 made for the same species. The 

 term "apparent abundance" (Marr 

 1951) refers to that portion of total 

 abundance that is available to the 

 fishery. 



