Abundance of Pelagic Resources Off California 

 1963-78, as Measured by an Airborne 

 Fish Monitoring Program 



JAMES L. SQUIRE, JR. 



ABSTRACT 



From September 1962 through December 1978 commercial aerial fish-spotter pilots operating off southern 

 and central California and northern Mexico, maintained a flight log indicating the geographical areas 

 searched and an estimate of the quantity of pelagic species observed. These flight logs were analyzed for quan- 

 tities of the various species observed per block area (10' longitude by 10' latitude area). Flights were recorded 

 as surveying all or a portion of 164,753 block areas. A total of 1 10,375 block areas were surveyed during the 

 da\ and 54,378 during night operations. An annual index of apparent abundance (arbitrary values) w as com- 

 puted for each of the major species observed, both for day and night aerial observations from selected geo- 

 graphical areas, and for total observations. The index value computed is not directly comparable between 

 species. 



During the period of the survey, the apparent abundance index for Pacific sardine, Sardinops sagax caeru- 

 lea, declined from 1.03 in 1964 to 0.00 in 1974, and no significant schools have been observed by aerial surveys 

 since. The northern anchovy, Engraulis mordax, night apparent abundance index remained relatively constant 

 from 1963 to 1969 (2.99-4.35), increased substantially in 1973 to 14.99, then declined by 1978 to a level (1.91) 

 near that observed in 1963-69. The day index for Pacific bonito, Sardachiliensis, declined to a low level in 1968- 

 69 (0.43-0.26), increased in 1972 to 1.11 (a year of above average sea surface temperature), and in subsequent 

 years declined again to a low level (±0.1). Pacific mackerel. Scomber japonicus, population biomass was 

 apparent!} low in 1962 at the start of the surveys, and continued to decline to very low night abundance levels 

 during 1967-75 (undefined range of 0.00 to 0.03). In 1976 a small increase in the overall apparent index was 

 recorded. By 1977 the night index had increased to 2.62, and in 1978 it again increased to a high level of 7.46. 

 Jack mackerel, Trachurus symmetricus, showed a declining abundance index value during 1969-75 (0.66-0.40). 

 A small increase in the night index apparent abundance was noted in 1976, and in 1977 the night index 

 increased to 2.77. In 1978 it then increased about 1.5 times to a record high of 4.20. 



Downward trends in apparent abundance indexes were noted 1 to 2 yr in advance of declines in the 

 commercial catches for northern anchovy and Pacific bonito. Limitations of collected nonrandom data and 

 variations in sightings and school size estimation between pilots are discussed. The apparent abundance 

 indexes obtained from aerial surveys are compared with measures from larval and acoustical surveys. 



A rank correlation analysis w as made to measure the agreement between independent estimates of north- 

 ern anchovy spawning biomass, larval index, and aerial index. Significant correlations were found for the aer- 

 ial and acoustical survey indices of 1972-78 for the northern anchovy (r v = 0.810, significant at the 0.05 level). 

 During this period only three larval surveys were conducted, insufficient to calculate correlation. For earlier 

 data, 1962-66 and 1968-69, larval vs. aerial index gave a poor correlation ( + 0.30). A significant correlation 

 was evident for Pacific mackerel aerial index vs. spawning biomass index (r s = 1.00). 



INTRODUCTION 



The Southwest Fisheries Center, National Marine Fisheries Serv- 

 ice (XMFS). initiated an aerial pelagic fish monitoring program in 

 1962 with the cooperation of fish-spotter pilots active in locating 

 fish for the central and southern California commercial purse seine 

 fishery. The program utilized the services of the aerial fish-spotter 

 pilot as a spin-off from their major occupation. The objective of the 

 monitoring program was to measure and evaluate the apparent 

 abundance of pelagic near-surface schooling fishes. 



It was originally hypothesized that basic sighting data for the var- 

 ious species— tonnage estimates, or numbers of schools and their 

 individual tonnage estimates, compared with search effort— would 

 provide a measure of the relative apparent abundance of each spe- 

 cies within a fishing area. Such information would be useful in 

 assessment of the available stocks. Since sighting information from 



'Southwest Fisheries Center La Jolla Laboratory, National Marine Fisheries Serv- 

 ice, NOAA, La Jolla. CA 92038. 



the spotter pilots is used as an aid in fishing, the efficiency of the 

 pilot in locating schools and sometimes directing the setting of the 

 purse seine has affected the catch per effort of the purse seiner. 

 Therefore, aerial spotter data may be more useful than fishing ves- 

 sel records for detecting changes in abundance of intensively fished 

 species. The aerial fish-spotter also records the abundance of 

 pelagic species which may not currently be targeted upon by the 

 fishery. Aerial survey data, therefore, can be particularly useful in 

 evaluating underutilized pelagic near-surface schooling resources. 

 The first report on the results of the program (Squire 1972) 

 reviewed trends in apparent abundance for data collected from 1962 

 through 1969. This review updates these data through 1978 using 

 the same analytical methods. Since publication of the first review, 

 considerable changes in the apparent abundance levels of some 

 pelagic species has occurred. The species of interest to this program 

 are all members of a complex, interacting coastal ecosystem, and 

 these data may assist in better defining changes in abundance levels 

 over time which occur within the coastal pelagic resources com- 

 plex. For a definition of terms used such as abundance, apparent 

 abundance, and relative apparent abundance, see Marr (1951). 



