program that variation in estimating school size probably has more 

 effect on the data than other variables. Some spotter pilots consist- 

 ently report greater tonnages than do others (Squire 1972). Six of 

 the fish-spotter pilots have continued full-time with the program 

 since 1963 and were the major contributors. Therefore, if biases in 

 reporting of tonnage were present, it may have been relatively con- 

 sistent throughout the period. MacCall, 3 in an investigation of aer- 

 ial spotter variation in reported abundance of anchovies, found that 

 differences in spotting power appeared to be consistent for both day 

 and night conditions for two periods of time (1 '/> yr apart). He also 

 stated that variability in reported tonnages was high even for con- 

 secutive flights, giving wide confidence intervals of estimates of 

 sporting power and daily fish abundance. A long-term averaging, 

 however, will reduce the variance in estimates of mean abundance. 

 In evaluating comparative observations between pilots as presented 

 in the flight log, we do not know if they were looking at the same 

 school or school group at the same time. If they were observing the 

 same school or school group, it is possible that some period of time 

 may have elapsed between observations, and the availability level 

 changed. Estimation values between pilots may also change by spe- 

 cies, requiring corrective factors by pilot for each species. For 

 example, the anchovy is sometimes one of the more difficult spe- 

 cies to evaluate and estimate tonnage because of the large school 

 groups and large tonnages available. 



Pilot estimation values for anchovy were calculated using data 

 for the period 15 September to 31 December 1966, 1969. 1974, 

 1976, and 1977. Flight logs of two or more spotter pilots were com- 

 pared, using observations thought to be near the same geographical 

 location, for either day or night. One aerial spotter, recognized 

 among his peers as an able and competent observer, was selected as 

 the key observer and his observations were used as a reference 

 base. The results for observations for other spotter pilots indicate 

 that, when compared with the key aerial spotter, two pilots were 

 estimating nearly the same as the key pilot, three were 0.4 times his 

 estimate, two were 0.45 times, and three about 0.08 times. The dif- 

 ferences in spotting power appeared to be consistent both day and 

 night, as found by MacCall (footnote 3). 



Aerial spotter pilots tended to survey portions of the ocean near 

 their bases of operation: either the greater Los Angeles area or the 

 Santa Barbara coastal area. Pilots operating in the same area tended 

 to estimate the available tonnage in similar amounts, for they fre- 

 quently communicated via radio and tended to cooperate in the 

 searching and fishing operations in their respective search and fish- 

 ing areas. As indicated previously, no effort was made during the 

 period of the survey to attempt to influence the individual aerial 

 spotters tonnage estimation values and the major contributors to the 

 program have participated throughout its 16-yr period. 



Comparison of Apparent Abundance Measuring 

 Techniques 



A precise measure of a specie s total abundance and its biological 

 composition is most desirable for the management of pelagic 

 marine species. However, at the present time a precise measure of 

 abundance is not possible. Management must therefore rely on 

 sampling techniques to obtain a reasonable estimate of abundance 

 and biological composition. The major coastal pelagic resources 

 are conveniently being measured by methods of sampling which 



provide a measure or index of apparent abundance (catch or obser- 

 vations per effort). Larval surveys provide an apparent abundance 

 measure, and acoustical surveys are conducted to determine the 

 apparent abundance of fish schools. These apparent abundance 

 indices are then adjusted to yield an estimate of total abundance. 

 For the years since the start of the aerial survey program, some data 

 are available giving estimates for Pacific mackerel and northern 

 anchovy. These data can be compared with the trend of the aerial 

 apparent abundance index. Three types of independent survey data 

 are available for comparison: the larval survey, acoustical or sonar 

 surveys, and the aerial spotter surveys. For the following species, 

 some comparative data are available. 



Pacific Mackerel 



Smith and Richardson (1977) presented a graph of three indepen- 

 dent estimates of the abundance of Pacific mackerel (Fig. 62) using 

 three index values: spawning biomass, larval index, and aerial 

 index. The aerial index can only be compared with values obtained 

 after the start of the aerial survey in 1963. A rank correlation test 

 (Spearman) was used to examine the aerial index vs. spawning bio- 

 mass (1963-67), giving a significant correlation (i\= 1.00). For the 

 aerial index vs. larval index comparison, the correlation coefficient 

 was r, = 0.77, not significant at the 0.05 level. Although the statis- 

 tics show promising results, it should be noted that the data are lim- 

 ited by the number of years tested, and that the three indices show a 

 common decrease in value. 



Northern Anchovy 



Three research programs using different techniques have inde- 

 pendently developed apparent abundance data concerning the 

 anchovy resource. Larval catch data have been summarized to pro- 

 duce a larval index and an estimate of spawning biomass. Acous- 

 tical surveys to measure school number and size have been used to 

 develop an acoustical index and an estimate of biomass. Aerial sur- 

 vey data have been used to develop an index of apparent abun- 

 dance. The larval and acoustical techniques sometimes used 

 different indices through the years. 



Since all estimates are independent of each other, an analysis was 

 made to determine if these methods were estimating a common 

 source. A description of the data sources for Figure 63 is as fol- 

 lows: larval abundance data for the central subpopulation for 1963 

 through 1972 was provided by Smith. 4 and data from 1972 through 

 1978 by Stauffer (1980). Acoustical surveys have been conducted 

 since 1966, but acoustical techniques were changed in 1971. 

 Therefore, acoustical data were compiled from Mais (1974. foot- 

 note 5). Aerial survey data taken off the coasts of southern Califor- 

 nia and northwestern Baja California, Mexico, from published 

 records 1962-69 (Squire 1972), and records through 1978 included 

 in this publication, are in Table 2. Figure 63 shows the larval index 

 from 1963 to 1978. for the central subpopulation. the aerial night 

 index, and acoustical index. The acoustical index is based on 

 TVx 10 3 schools for the early years, and the school's surface area 

 (square nautical miles) for the later years. The larval index uses the 

 estimated abundance of larvae x 10 i: for the central subpopulation. 



3 MacCall, A. 1975. Investigation of aerial spotter variation in reported abun- 

 dance of anchovies. Anchovy Workship Meeting. July 21-22, 1975, contrib. 19. 3 

 p. Southwest Fisheries Center La Jolla Laboratory, NMFS, NOAA, La Jolla, CA 

 92038. 



4 P. E. Smith. Fishery Research Biologist. Southwest Fisheries Center La Jolla 

 Laboratory. NMFS. NOAA. La Jolla. CA 92038, pers. conimun. 1974. 



5 Mais, K. F. 1978. Acoustic survey for the assessment of anchovy resources off 

 California and northern Baja California. Unpubl. manuscr. . 21 p. California 

 Department of Fish and Game. Marine Resources Laboratory. 350 Golden Shore. 

 Long Beach. CA 90802. 



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