314 



Fishery Bulletin 91(2), 1993 



300 



1945 1950 1955 1960 1965 1970 1975 1980 1985 



Year ' 



1945 1950 1955 1960 1965 1970 1975 1980 1985 



Year 



100 200 300 



Spawning biomass 



Figure 3 



Recruitment of the chub mackerel Scomber japonicus 

 stock off southern California, (a) Time trajectories 

 of recruitment R ( 10* lb) and spawning biomass P 

 (10* lbi; (b) time trajectory of log (RIP); (c) 

 stock-recruitment scatterplot, in same units as (a). 



other pesticides. The sharp rise in pesticide use in the 

 1950s and the subsequent decline in the 1960s and 

 1970s are similar for many of these compounds, which 

 leads to difficulty in distinguishing their effects statis- 

 tically. The PCBs, a group of non-pesticide toxic or- 

 ganochlorine compounds, have been used increasingly 

 throughout most of this century, but little is known 

 about the volume of their use and discharge before 

 1960. 



Loadings of metals have varied with growth of the 

 human population and also with fluctuations in pat- 

 terns of industrial use. Loadings of some particularly 

 toxic metals, such as lead and cadmium, have declined 

 recently because of environmental regulations. 



Most of the historical reconstructions of Summers et 

 al. (1988) included values for all years from 1946 

 through 1981, but some contaminant variables lacked 

 values for 1981. We extrapolated from immediately- 



