being determined by past experience regarding the most likely loca- 

 tions for sighting schools of various species, real-time information 

 from fishing boats and other spotter aircraft, and other recent exper- 

 ience. The species identification of the schools was determined 

 during the day by physical characteristics such as shape or color of 

 the fish or school, or by behavior of the fish. During the night, 

 identification was made by the bioluminescent characteristics of the 

 school's shape or its behavioral response to a flash of light. Infor- 

 mation from fishing vessels was sometimes used in determining 

 species composition, particularly where "mixed schools" were 

 encountered. 



A pilot's estimate of school tonnage is based on many years of 

 observing school size, shape, depth, and quantity as determined by 

 catching the fish observed. It is possible to estimate a school's verti- 

 cal depth (distance from top of school to bottom) for schools of the 

 larger pelagic species and small schools of such species as the 

 northern anchovy. However, for large schools of the smaller forage 

 species, the actual depth of the school usually cannot be determined 

 from the air. Therefore, information from fishing vessels was fre- 

 quently used since they could determine the school's vertical depth 

 using an echosounder. The horizontal shape and area of the school 

 could be estimated visually. Aerial spotter pilots are often paid on 

 the basis of tonnage caught, so a close check on tonnage taken by 

 the purse seiner is important to the pilot. 



SIGHTINGS AND ABUNDANCE INDEX 

 TRENDS BY SPECIES 



Geographical Distribution of Fish School and 

 School Group Sighting 



Current and historical records, based on catch or fishing boat log- 

 book data, give some indication of the location of catch, but only by 

 "block area" (a 10' longitude x 10' latitude area), which measures 

 about 8x10 nmi each at the latitude of southern California. A more 

 detailed description of individual locations of the center of school 

 or school group sightings as observed on each flight (day plus 

 night) for the period 1962 through 1978 is given in Figures 4-61. 



An illustration of how the center of sighting was determined is 

 given in Figure 3 . The dot on the chart is the geographical center of 

 the sighting, representing one or more animals or schools observed 

 in the area. On some charts having a high density of sightings, an 

 overlap or masking may occur, particularly for anchovy. 



Locations of centers of sightings are given for the northern 

 anchovy (Figs. 4-1 1), Pacific sardine (Figs. 14-18), Pacific bonito 

 (Figs. 20-27), Pacific mackerel (Figs. 30-36), jack mackerel (Figs. 

 38-45), bluefin tuna (Figs. 47-49), albacore tuna (Figs. 50 and 51), 

 yellowtail (Figs. 52 and 53). Pacific barracuda (Figs. 54 and 55), 

 white seabass (Figs. 56 and 57), basking shark (Figs. 58 and 59), 

 and squid (Figs. 60 and 61). 



A review of the sighting distribution charts is given in the follow- 

 ing sections for those areas having the most sightings. In many 

 instances the charts for north of Morro Bay and those below the 

 United States-Mexico border are not shown because the observa- 

 tion effort was low, or the effort was not expended in areas where 

 the species of interest would be commonly observed. For example, 

 anchovy charts are not given for the Monterey Bay area because, 

 although anchovies have frequently been observed in the area, the 

 observation effort since the mid-1950 s has been low. Most of the 

 flight observation effort south of the United States-Mexico border 

 has been offshore in search of bluefin tuna, and, as a result, 

 nearshore areas commonly having schools of anchovies are rarely 

 surveyed and are therefore not given. 



During the survey period, the following total number of sightings 

 of schools or school groups were made: northern anchovy. 8,720; 

 Pacific sardine, 195; Pacific bonito, 3,873; Pacific mackerel. 

 1.273; jack mackeral. 3,233; bluefin tuna. 1.314; albacore tuna, 

 200; yellowtail, 94; Pacific barracuda, 138; white seabass. 70: and 

 squid, 384. The observations of schools or school group for the 

 major species observed represent a total tonnage sighted by day and 

 night of 43.013,254 t of northern anchovy; Pacific sardine. 

 442,644 1; Pacific bonito, 442,644 1; Pacific mackerel 1 ,364.048 t: 

 jack mackerel 1,869,256 t; and bluefin tuna, 507.366 t. 



Apparent Abundance Index Trends 



Day and night indices of apparent abundance for each zone and 

 grouped zones have been calculated annually since 1963 forspecies 

 of northern anchovy. Pacific bonito, jack mackerel, Pacific mack- 

 erel. Pacific sardine. Pacific barracuda, and yellowtail. Bluefin 

 tuna indices have been calculated since 1974. 



In calculating the index value, one of four arbitrary tonnage 

 ranges for each species was assigned. These cover the range of 

 observed tonnages that might be estimated to occur in any one 

 block area. In order to provide a tonnage range value (,v) the mid- 

 point of each range was divided by 100 forthe northern anchovy, a 

 species that is observed in larger quantities compared with any oth- 

 ers and by 10 for Pacific bonito, jack mackerel. Pacific mackerel. 

 Pacific sardine, and bluefin tuna. The midpoint of the tonnage 

 range for yellowtail and white seabass was not reduced. The range 

 of observed tonnage and resulting .rvalues are given in Table 2. The 



Table 2.— Range of tonnage and tonnage range values 

 (A). A' is the index value based on the midpoint of the 

 observed tonnage/100 (but not for barracuda or yel- 

 lowtail). 



Species 



Observed tonnage 



A' 



Anchovy 



0-400 



2 





401-1.000 



7 





1.001-10.000 



55 





10.001-20.000 



150 



Pacific bonito 



0-50 



2.5 





51-150 



10 





151-1.000 



57.5 





1.001-5.000 



300 



Jack mackerel 



1-50 



2.5 





51-300 



17.5 





301-1.000 



65.5 





1.001-2,000 



150 



Pacific mackerel 



0-20 



1 





21-100 



6 





101-250 



17.6 





251-500 



37.5 



Pacific sardine 



0-100 



5 





101-500 



30 





501-2.000 



125 





2.001-4,000 



300 



Bluefin tuna 



0-50 



2.5 





51-250 



15 





251-1.000 



62.5 





1,001-4,000 



250 



Pacific barracuda 



0-10 



5 





11-30 



20 





31-80 



55 





81-160 



120 



Yellowtail 



0-5 



2.5 





6-10 



7.5 





11-30 



20 





31-60 



45 



