Squire: Aerial monitoring of abundance of pelagic fishes 



355 



Northern anchovy (Fig. 2) The core area index (night 

 index) was near 180 T/BAF in the mid- to late-1960s. 

 The index increased in the early 1970s, and during 

 1972-80 remained in the range of 450-700 T/BAF. The 

 index began to decline in 1980 and reached a low level 

 of abundance by 1983 (<50 T/BAF), a level consider- 

 ably below that observed in the mid-1960s. 



Northern Anchovy 

 Core Area Zones 



AERIAL INDEX we^hled 



Figure 2 



Abundance index levels in T/BAF for northern anchovy 

 Engraulis mordax core area, night index, weighted x, and 

 running average ( x3). 



Pacific sardine (Fig. 3) The Pacific sardine resource 

 was in a state of decline at the time the aerial spotter 

 program was started. Average tonnage calculated for 

 the 1963-66 period for the core-area index was 1.03 T/ 

 BAF. Very low abundance indices were recorded from 

 1967 until the early 1980s with some years reporting 

 zero sightings of sardine schools. The core-area run- 

 ning mean index (night index) increased to 60 T/BAF 

 by 1988. 



Pacific Sardine 

 Core Area Zones 



AVG WEIGHTED X 

 1982-38-37 7TBAF 



_tei^ 



$6 68 70 72 74 76 



Figure 3 



Abundance index levels in T/BAF for Pacific sardine Sardinops 

 sagax core area, night index, weighted x, and running aver- 

 age (  3 1. 



Pacific bonito (Fig. 4) Abundance levels for Pacific 

 bonito show considerable fluctuation. Bonito were 

 rarely taken off southern California prior to the strong 

 El Nino of 1957-58 (Radovich 1960). They were com- 

 mon in southern California waters after this event 

 and were intensively fished starting in about 1963. 

 The increase in fishing effort redirected to this species 

 was the result of decreased abundance of Pacific sar- 

 dine and chub mackerel. 



The core-area index value (day index) reached a 

 high in 1966 of 10.5 T/BAF. This is the highest in- 

 dex value recorded for bonitd during 1962-90. The 

 index then declined, increased slightly in 1972 to 

 3.2 T/BAF, and substantially increased in 1984 to 

 5.5 T/BAF. 



Figure 4 



Abundance index levels in T/BAF for Pacific bonito Sarda 

 chiliensis core area, day index, weighted x, and running aver- 

 age (X3>. 



Chub mackerel (Fig. 5) Declining abundance levels 

 noted in the early to mid-1960s matched the collapse 

 of the fishery, with extremely low index levels (>5 T/ 

 BAF) noted for the core-area index (night index) in 

 1967-75. After 1976, the abundance index rose rapidly 

 to a peak of 170 T/BAF in 1978, then declined to a 

 range of 15-55 T/BAF in 1981-89. 



Jack mackerel (Fig. 6) Abundance was high during 

 the mid 1970s. The core-area index (night index) in- 

 creased to 234 T/BAF in 1976 and declined to <10 T/ 

 BAF after 1979. 



Bluefin tuna (Fig. 7) For the core area, there were 

 three peaks in the index (day index) of abun- 

 dance: 1967, 1973, and 1978. The index for recent 

 years is well below the 1963-88 average of 10.8 T/ 

 BAF. 



