Prager and MacCall. Contaminant and climate effects on spawning of three pelagic fishes 



313 



0.5 1.0 1.5 



Spawning biomass 



2.0 



Figure 1 



Recruitment of the northern anchovy Engraulis mordax 

 stock off southern California, (a) Time trajectories of 

 recruitment R ( 10 s fish I and spawning biomass P (10 fi t); 

 (b) time trajectory of log lR/P); (c) stock-recruitment 

 scatterplot, in same units as la). 



Methot's estimates of spawning biomass on 15 Feb- 

 ruary of each year. For recruitment, we used 

 Methot's estimates of the number of recruits on 1 

 July of the same year. Methot stated that his esti- 

 mates of recruitments before 1964 are much less 

 precise; we used his estimates of 1964 through 81 

 (the end of the contaminant data series). 



Stock and recruitment data on Pacific sardine 

 (Table 1, Fig. 2) are the estimates of MacCall 

 (1979, Table 3), and were derived from fishery 



statistics. Although the estimates extend through 1964, 

 MacCall (1979) discounted the 1963 and 1964 estimates of 

 recruitment as not sufficiently precise. We used the esti- 

 mates from 1946 (the beginning of the contaminant series) 

 through 1962. 



Stock and recruitment data on chub mackerel (Table 1, 

 Fig. 3) are from Table 1 of Prager & Hoenig (1989), who 

 compiled data from MacCall et al. ( 1985), Parrish & MacCall 

 (1978), and Prager & MacCall (1988a). The estimates, all 

 derived from fishery statistics, were adjusted by Prager & 

 Hoenig (1989) to a common reporting date. The temporal 

 limits of our analysis, 1946-81, were determined by the lim- 

 its of the contaminant series. The chub mackerel data span 

 a stock collapse and subsequent closure of the fishery and 

 thus have 6yr (1969-74) of data missing. Nonetheless, the 

 chub mackerel series (n=30) is the longest of the three stocks. 

 The data encompass at least two distinct epochs in the ex- 

 istence of the population: the pre-collapse epoch of steadily 

 increasing exploitation rate, and the post-collapse epoch of 

 more strictly regulated fishing and the associated popula- 

 tion increase. 



Explanatory data: Contaminants 



Historical contaminant-loadings data were compiled and re- 

 constructed by Summers et al. (1988) according to a 

 mass-balance approach based on manufacturing volume, land 

 use practices, and mobility of particular contaminants. Sum- 

 mers et al. (1988) also compiled more general measures (e.g., 

 wastewater flow) from governmental records. The resulting 

 annual time-series include five major categories: gross in- 

 dicators, physical-biological factors, nutrient loadings, or- 

 ganochlorine loadings, and metal loadings (Table 2). Prager 

 & MacCall (1990) discussed the loading patterns of indi- 

 vidual contaminants and provided time-series plots of each; 

 here, we review major characteristics abstracted from Sum- 

 mers et al. (1988) and Prager & MacCall (1990). 



The human population of southern California has increased 

 sharply over the last 50 yr, and this is reflected in many 

 contaminant-loading patterns, particularly in the first three 

 categories (Table 2). For example, loadings of nitrogen, phos- 

 phorus, and total organic carbon arise principally from waste- 

 water (sewage) flow, which has increased with population 

 size; power-plant cooling flows, for the most part, also re- 

 flect the growing population's use of electricity. While size of 

 the annual kelp harvest is strongly correlated with human 

 population size, the relationship may be noncausal; this is 

 impossible to ascertain statistically. Nonetheless, size of the 

 kelp harvest was included among other potential indicators 

 of environmental stress, as many species are present in kelp- 

 forest habitat during early stages of life history. 



With the exception of PCBs, the organochlorines listed in 

 Table 2 were all introduced in the late 1940s. Most fluc- 

 tuations in individual loadings have followed legal restric- 

 tions on use (e.g., of DDT) and subsequent increased use of 



