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Fishery Bulletin 91 [2). 1993 



Interaction between species 



To compare periods of high and low abundance of 

 the six species, the logarithm of the moving weighted 

 averages of core-area abundance indices (day or night, 

 dependent upon which time the species was observed 

 more frequently and in greater quantity) were plotted 

 (Fig. 8). The dominant feature of Fig. 8 is the abun- 

 dance index for the northern anchovy. High index lev- 

 els of 200-500 T/BAF were recorded during 1962-82, 

 a 21 yr period. The index declined sharply in 1983 and 

 1984, increasing since. The northern anchovy is the 

 more stable species in terms of less annual percentage 

 change in abundance than any of the other five spe- 

 cies. During 1966 and 1967, jack mackerel, bluefin 

 tuna, and Pacific bonito were at higher levels of abun- 

 dance than those observed in the early 1970s. The 

 Pacific sardine and chub mackerel resources were low 

 in abundance by 1965, and declined to extremely low 

 levels by 1970. The northern anchovy, jack mackerel, 

 chub mackerel, and bluefin tuna increased in abun- 

 dance in 1974-79. Exceptions were the Pacific bonito 

 and sardine. 



The very strong El Nino condition of 1982-83 (Quinn 

 et al. 1987) had a significant effect on the distribution 

 of coastal pelagic species (Fluharty 1984, Squire 1987). 

 This period saw declines in abundance for all species, 

 except Pacific bonito and chub mackerel. These two 

 species showed significant declines in 1986-87. A rapid 

 increase in Pacific sardine abundance was evident in 

 1984, immediately following the El Nino event and 

 continuing into the late 1980s. 



