FISHERY BULLETIN: VOL. 84, NO. 2 



METHODS 



Aerial surveys were flown at an altitude of 1,000 

 ft ASL (328 m) at about 90 kn (167 km/h) in a high- 

 wing, twin-engine Cessna 2 337. The crew consisted 

 of a pilot and three experienced marine mammal 

 observers, one acting as recorder. Surveys were 

 flown along 15 parallel, predetermined tracklines, 

 separated by 15 nmi and extending from the shore 

 to a maximum distance of 100 nmi (185 km; Fig. 1). 

 Tracklines were oriented from northeast to south- 

 west and were roughly perpendicular to the shore- 

 line, as well as to most major features of submarine 

 topography in the study area. Whenever possible, all 

 transect lines were surveyed on each 3-d flight. 

 Transect lines were not replicated on a single survey, 

 nor were they flown in a predetermined order or 

 direction. The first line flown on a given day was oc- 

 casionally dictated by weather or military activity 

 in the area; subsequent lines were chosen to optimize 

 coverage and simplify logistics. 



Observers searched unbounded corridors on each 

 side of the aircraft trackline Sightings were recorded 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



and coded for computer entry at the time of occur- 

 rence The aircraft was diverted to circle those 

 schools located off the trackline for positive iden- 

 tification, animal count, and photographs. The total 

 animal count recorded for each school was a consen- 

 sus of the observers on board, derived from multi- 

 ple orbits of the school. Any additional sightings ob- 

 tained while "off transect" were not included in later 

 density calculations due to the possibility that the 

 secondary sighting was prompted by the first. All 

 transect segments where observer effectiveness 

 might have been hampered by fog and/or sea state 

 were deleted from the data base; only transect seg- 

 ments where visibility exceeded 1 nmi and the sea 

 state was Beaufort 3 (few, scattered whitecaps) or 

 less were retained. 



Aerial photographs were used to validate observ- 

 er estimates of school size. The aerial photographs 

 were taken on 9" x 9" film from a vertically mounted 

 camera and on 4" x 5" and 35 mm films in hand- 

 held cameras for oblique views. The large, 9" x 9" 

 vertical photographs soon proved to be the most 

 useful and were used almost exclusively for count 

 verification. Observer counts and film counts on 

 average-sized schools (up to 100 animals) varied only 

 slightly, but not in a consistent manner. The 3-5% 



121 



120" 



119" 



118" 



117" 



SOUTHERN CALIFORNIA BIGHT I 



n 120 119" 118" 



Figure 1.— Map of the Southern California Bight study area showing aerial survey tracklines. 



334 



