Albacore were sometimes sighted west and southwest of San 

 Diego (Fig. 50). but few sightings were made north of this area. A 

 total of 124 sightings were made during the survey period. Figure 

 51 indicates that 76 sightings were made west to northwest of 

 Ensenada, but few were made in this area south of a line drawn west 

 from Cabo Colnett, Mexico. 



Other sightings 



Although yellowtail. Pacific barracuda, white seabass. basking 

 shark, and squid are not of primary interest to the commercial aerial 

 fish spotter, records were maintained and are given for these species 

 because they are of interest to the recreational or commercial fish- 

 eries of southern California. 



Yellowtail. — Areas of sighting were about the Coronado Islands. 

 Mexico, north to near Newport, along the northeast side of San 

 Clemente Island (Fig. 52), and along the coast from Santa Barbara 

 to Pt. Conception (Fig. 53) 



Pacific barracuda. — Small numbers of sightings were made 

 along the coast, from north of San Diego to near Long Beach, and 

 off the northeast side of San Clemente Island (Fig. 54). Barracuda 

 were also sighted along the coast from near Pt. Conception to Ven- 

 tura (Fig. 55). 



White seabass. — This species was more commonly sighted by 

 the aerial spotters near Pt. Conception, along the north side of 

 Santa Cruz Island (Fig. 56). and to the north off Avila. Morro Bay 

 (Fig. 57), with some sightings recorded in the northern half of 

 Monterey Bay. 



Observations of basking shark (Figs. 58. 59) and of squid (Figs. 

 60, 61) are of interest to the commercial fishery and are given. 

 Index values are not given for these species. 



DISCUSSION 



Evaluation of Index Data 



The aerial observation program relies on the assistance of 

 commercial aerial spotters who, for a modest fee, provide flight log 

 data. The limitations of the data must be recognized since they are 

 nonrandom, and influenced by many variable factors. 



Sighting. — The probabilty of sighting a school may be affected 

 by a number of physical factors, some of which are common to both 

 day and night operations, others to day or night (see Table 4). Eco- 

 nomic factors are also very important in determining target species 

 for search and location of area searched. In recent years, the 

 demand for anchovy has increased and additional emphasis has 

 been placed on searching areas where anchovy are commonly 

 observed. However, these areas are frequently the same areas 

 where other species are observed. 



Table 4.— Physical factors affecting the probability 

 of sighting a school. X = important. — = less impor- 

 tant, and = not a factor. 







Day 



Night 



Area observed 





X 



X 



Angle of viewing 





X 



— 



Sun position 





X 







Moon phase 









X 



School size 





X 



X 



School depth 





X 



X 



School density 





X 



— 



Bioluminescence 



levels 







X 



Weather 









clear 





X 







overcast 





X 







haze 





X 



— 



Configuration of 



lire raft 



X 



X 



Ground speed differences 



- 



- 



Basking shark. — Although many species of sharks were 

 sighted, most were not indentified by the spotter pilots as to spe- 

 cies. The exceptions were the large sharks, such as the basking 

 shark which was the subject of a commercial fishery in the late 

 1940s and early 1950s. Aircraft were used in this fishery to locate 

 basking sharks and. on occasions, great white sharks were 

 observed (Squire 1967). 



Basking sharks were quite common in coastal waters in the late 

 1940s and early 1950s, and at that time were fished commercially 

 in California. They were sighted frequently off Avila and Morro 

 Bay (Fig. 58) along the coast south of Pt. Sur, but most frequently 

 in the central and northern half of Monterey Bay (Fig. 59). Few 

 were observed in the mid- to late- 1960 sand early 1970s. Recently, 

 more basking sharks were being sighted north along the coast from 

 the Santa Barbara area west to Point Conception. A total of 1 .91 1 

 basking sharks were recorded by the aerial spotters. 



Squid. — The only invertebrate animal reported as being sighted 

 in surface schools was the squid. Schools were most common about 

 the eastern half of Santa Cruz Island and Anacapa Island (Fig. 60). 

 and in the coastal area from Pt. Hueneme to Pt. Dume. They 

 appeared most common about Catalina Island (Fig. 6 1 ). w ith larger 

 concentrations along the southwest side. Distribution of sightings 

 about San Clemente Island were grouped at the northwest and 

 southeast ends. 



Identification. — The detection of near-surface schools during 

 the day is dependent upon the pilots ability to distinguish subtle 

 color and light intensity differences in the water. Detection of 

 schools at night is possible only during the dark phase of the moon, 

 and depends on the pilot's ability to discern gradation of light inten- 

 sity. Bioluminescence of planktonic organisms agitated by school- 

 ing fish indicates by a dull glow the location and size of the school. 



Species are identified during the day on the basis of a combina- 

 tion of two or more of the following characteristics: color of school 

 or individual fish, shape of school, and behavior and size of indi- 

 viduals within the school. At night, species identification is based 

 on shape of the luminous area and behavior of the schooling fish 

 under undisturbed conditions, or by the behavior of the school after 

 being subjected to a stimulus from an external source such as a 

 flash from the aircraft's landing light. A light flash causes a 

 response or movement of the fish, which agitates the plankton, 

 resulting in bioluminescence. The response of the fish to the light 

 flash is species-distinctive and allows the trained observer to make 

 an estimation of species. The level of bioluminescent plankton 

 organisms, the schooling configurations, depth of school, and com- 

 position of the school (mixed species), are some of the variables in 

 night identification. 



School size estimation. — The probability of sighting, identify- 

 ing, and estimating school size, is affected by the training and abil- 

 ity of the spotter pilot. It was recognized in the beginning of the 



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