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Fishery Bulletin 91(2). 1993 



the area or numbers of schools with an estimate of the 

 tonnage of each school. Procedures for recording spe- 

 cies observations and survey effort have not changed 

 since 1962. Other information such as time of flight 

 (day or night) and flight duration also are recorded on 

 the flight log. Flight logs are submitted quarterly and 

 data from each log are entered into the computer after 

 editing. 



Spotter pilots' income is derived from the commer- 

 cial fishery at a current rate of -6% of the vessel's 

 gross income. Spotter pilots are paid a nominal fee by 

 the National Marine Fisheries Service (NMFS) to 

 maintain a flight log record of their observations. 

 Pilots in the program averaged ~600h flight time/yr 

 and, with 4-6 pilots, the total number of hours flown 

 was ~3000/yr. 



From 1963, the first full year of operation, to 1990, 

 annual indices of abundance for each species were 

 calculated for the total area (from northern Baja Cali- 

 fornia, Mexico to San Francisco, California) and for 

 selected groups of 10" lat. x 10" long, block areas, 

 similar to the "block area" statistical system used by 

 CDF&G (Anon. 1935). These groups of block areas 

 are referred to in this paper as "zones" and were 

 designed to encompass important commercial fishing 

 areas (Fig. 1). 



Flight effort for the total area and each zone was 

 determined by counting the number of times the aerial 

 spotter's flight track entered a block area, termed a 

 "block area flight" (BAF). Species abundance was re- 

 corded as the tonnage estimate (and hence approxi- 

 mates biomass) for the area observed. Also recorded 

 on the flight log was time of the observation (day or 

 night), pilot, and, since 1988, the target species of the 

 commercial operation. 



The procedure to measure effort has not changed 

 from previous studies; however, the computation of spe- 

 cies abundance has been modified. In previous analy- 

 ses (Squire 1972, 1983), abundance was estimated as 

 a rank index according to discrete incremental values 

 of tonnage (tonnage range values). For example, for 

 the northern anchovy, an observation within a block 

 area estimated to be 0-100t was recorded as 1, 100- 

 200t was recorded as 2, etc. Each species had different 

 tonnage range values, since the amount of tonnage 

 observed varied greatly between species. Therefore, the 

 abundance index values for each species are not di- 

 rectly comparable. For this analysis, actual tonnage 

 values as recorded by the spotter pilot and a modifica- 

 tion of the index used by Squire ( 1972) are used, which 

 allows for direct comparison of abundance index val- 

 ues between species. 



The apparent abundance index is T/BAF, where T = 

 tonnage estimate, and BAF = total number of block 

 area flights (day plus night, all zones). 



Results and discussion 



Observation effort and sightings 



During the period 1963-90, a total of 24 aerial fish- 

 spotter pilots participated in the program and reported 

 flight operations totaling over 67,000h, searching a 

 total of 376,446 block areas. Table 1 gives the annual 

 search effort (BAF/yr), day and night, during the pe- 

 riod 1962-90. From 1963 to 1990, a total of 253,239 

 BAF were made during day operations (67%) and 

 123,207 BAF during the night. Pilots have searched 

 an average of 13,444 BAF/yr; however, the variation 

 in annual spotting effort is considerable. There was 

 reduced effort in early 1970. Abundance data for 1970 



