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Fishery Bulletin 9 1 12). 1993 



sardine, most biomass studies and modeling for the 

 California region have involved the northern anchovy 

 (Methot 1989). 



Over the past 35 yr, studies by fishery biologists have 

 produced a wide range of population estimates for a 

 number of the pelagic species, in particular, the north- 

 ern anchovy, Pacific sardine, and chub mackerel. The 

 following describes the results of these and others in 

 relation to aerial abundance indices. 



Northern anchovy A review of the many abundance 

 estimates for the northern anchovy over the years 

 1940-66 was given by Messersmith et al. (1969). For 

 the early years of the aerial program, MacCall et al. 

 (1974) compared anchovy biomass estimates from egg 

 and larva surveys with the night aerial index, result- 

 ing in a correlation of +0.30 ( 1962-69). They also com- 

 pared the aerial night index with the acoustic esti- 

 mate (1966-72) producing a negative correlation 

 (r=-0.47). 



In a review of egg production of the northern an- 

 chovy central stock, Lo (1985) presented a correlation 

 between various indices of anchovy spawning biomass. 

 The biomass index from the aerial surveys had a high 

 correlation (r=0.818) with egg production, and there 

 was a similar correlation (r=0.807) between biomass 

 egg production and acoustic surveys. 



Correlation plots of normalized data (standard devi- 

 ates; Snedecor 1959) were used to compare northern 

 anchovy abundance data presented by Lo (1988) with 

 aerial index values. The aerial index (day plus night) 

 for the core area was compared with Lo's (1988) esti- 

 mate of spawner biomass, determined from a combi- 

 nation of various estimates from the egg production 

 method and the results of the 1969-85 sonar or acous- 

 tic surveys (Lo 1988), giving a correlation of r=0.61, 

 df=14, P<0.057c The aerial index was also compared 

 with the estimate of schooled biomass based on results 

 of acoustic surveys presented by Lo (1988), giving a 

 correlation of r=0.51, df=13, P<0.05%. 



MacCall & Prager (1988) presented anchovy larval- 

 abundance indices for 1963-85. These indices, which 

 are a measure of spawning population, were compared 

 with the core-area aerial index for the same set of 

 years. There was statistically significant correlation 

 between the two indices (aerial/larva) (r=0.82, df=13, 

 P<0.1). 



Pacific sardine MacCall & Prager ( 1988) also reviewed 

 the historical trend of sardine larval abundance, 1951- 

 85. A comparison was made between their arithmetic 

 scale of larval abundance (standard index) and the 

 aerial index during the period 1963-85. Indications of 

 a resurgence of the Pacific sardine resource began in 



1978, and for the 1963-85 period MacCall & Prager 's 

 ( 1988) estimate of larval abundance correlates well with 

 the aerial index (/-=0.98, df=8, P<0.01). 



Pacific bonito Pacific bonito, a species whose sea- 

 sonal abundance off California is more closely associ- 

 ated with environmental conditions (El Nino effects) 

 than the other species (Squire 1987), has not been 

 subjected to detailed assessment. MacCall et al. (1974) 

 used recreational partyboat CPUE data in yearly time- 

 lag periods and compared this with the aerial index. 

 The recreational partyboat fleet generally fishes 

 nearshore and catches younger fish than the offshore 

 commercial purse-seine fleet. The highest correlation 

 (r=0.69) between the recreational fleet CPUE and the 

 aerial index was for a 3yr lag period (aerial index lags 

 the recreational CPUE). No other independent esti- 

 mates of Pacific bonito biomass are available for com- 

 parison. 



Chub mackerel Assessment of the chub mackerel re- 

 source has used both standard population-dynamics 

 techniques and methods that utilize egg and larva sur- 

 veys. For comparison of changes in population over 

 time, Squire (1983) plotted the trend of the aerial in- 

 dex against the spawning biomass index and the larva 

 index of Smith & Richardson (1977). The limited data 

 (1963-67) precluded any long-term comparison; how- 

 ever, all three indices showed a similar decrease. The 

 aerial index was significantly correlated (P<0.05) with 

 both spawning biomass (r=0.99) and the larva index 

 (r=0.94). 



The chub mackerel biomass declined to very low lev- 

 els in the mid-1960s and remained very low until the 

 mid-1970s. A sharp increase in biomass was noted 

 starting in 1976. MacCall & Prager (1988) presented 

 data on chub mackerel larval abundance through 1985. 

 A correlation of the aerial index (core area) with the 

 larva index for 1963-81 was statistically insignificant 

 (r=0.205). A comparison made between the aerial in- 

 dex (core area) and estimated biomass of MacCall et 

 al. ( 1985) for 1963-84 gave what would appear to be a 

 good fit for the early years, but comparison of later 

 years' estimates was not significant (r=0.26). 



Jack mackerel Various indices of abundance for jack 

 mackerel, including the aerial index, show that the 

 resource tends to be highly variable in apparent abun- 

 dance. Egg and larva surveys have shown the stock to 

 be extremely widespread. Based on tagging data, 

 Knaggs (1973) estimated between 700,000 and 

 1,500,000 1 were available to the fishery in 1973. 

 MacCall et al. (1974) stated that these estimates are 

 in agreement with trends in aerial survey index (Squire 



