CALCOFI TIME SERIES: AN OVERVIEW OF FISHES

POPULATION PROCESSES The stated objective of CalCOFl is " to determine what controls variations in population size and availability in oceanic fishes off the west coast of North America. " The chief disciplines to be applied to this work are fishery biology-the study of population and biological community reactions to commercial harvest-and biological oceanography-the study of how the biological and physical environment affects biological populations and communities. Murphy (1966, p. 69) concluded that the Pacific sardine was overfished and that the virtually unfished anchovy had increased to f i l l its niche as a regionally dominant planktivore. However, the fossil-scale record (Soutar and lsaacs 1974). which is considered to be a useful index of population size and availability. shows that precipitous declines in the Pacific sardine population between 1930 and 1960 off southern California were exceeded between 1850 and 1870. when there was no fishery, and between 19OU and 1915. when the fishery was small. Smith (1972) reviewed the time series of sardines and anchovies as indexed by their larvae and concluded (p. 873) that the size-frequency curves of the larvae of the two species were so invariant among years that competition between the two species. if any. would most likely occur at the juvenilc and prerecruit stages of either species. This was contrary to the argument of lsaacs (1965) that the recruitment of anchovy and sardine could be projected from daylnight differences in the early larval stages. Smith (1972) also recommended that the ideas should be tested with surveys of larger larvae and juveniles. He pointed out that the number of batches of spawn per unit time might be plastic (Smith 1972. p. 873). This biases the indices of population size by failing to estimate the degree of interannual variation in the amount o f spawning per unit time per unit o f adult biomass. In this connection it was pointed out that the declinc of sardine spawning in the spring and bummer has coincided with an increase o f spawning in spring hy thc anchovy. Current estimates of historical hiomass (Lo 1985) indicate that apparent incrcasc in anchovy spawning biomass following the collapse of the sardine population could result from increased repetitive spawning as well as increased anchovy spawning biomass. Another element in variations in population size and availability of fishes is the biological community structure. Moser et al. (1987) showed that there were major changes in mesopelagic and epipelagic fish reeurrent groups during climatic changes. But data from only seven years ccntered on the 1957 El Nino were analyzed. so the longterm coherence of the changes cannot yet be assessed. For the same period, Colebrook (1977) showed that there were major shifts in the types of zooplankton, with particularly significant shifts in the north-south distribution of zooplankton and secondary changes in the onshore-offshore abundance. What are the critical time and space scales for understanding the fluctuations in abundance of oceanic fishes off the North American Pacific coast? Haury et al. (1978) suggest a rationale and design: