DETECTION OF CONTAMINANT AND CLIMATE EFFECTS ON SPAWNING SUCCESS OF 3PELAGIC FISH STOCKS OFF SOUTHERN CALIFORNIA - NORTHERN ANCHOVY ENGRAULIS-MORDAX, PACIFIC SARDINE SARDINOPS-SAGAX, AND CHUB MACKEREL SCOMBER-JAPONICUS

We describe a simple biostatistical model of reproductive success (log arithm of recruits/spawner) applied to three coastal pelagic fish stoc ks off southern California: northern anchovy Engraulis mordax, Pacific sardine Sardinops sagax, and chub mackerel Scomber japonicus. We used the model to detect possible influences of gross climatic conditions and contaminant loadings (particularly of metals and organochlorines) on reproduction in these three stocks. Data included several decades o f annual estimates of recruitment and stock size, monthly measures of climate, and annual estimates of contaminant loadings; the model inclu ded a compensatory stock-size component before adding environmental ef fects. The study was meant to generate, rather than test, hypotheses. For the chub mackerel stock, we detected climate influences, but no co ntaminant influences, on reproductive success, which was usually high during conditions typical of El Nino-Southern Oscillation events. For the northern anchovy stock, we detected no climate or contaminant infl uences on spawning success; however, the negative results may reflect low statistical power, rather than absence of contaminant influences. For spawning success in the Pacific sardine stock, we detected no cons istent climate influences, but we found a strong negative correlation with contaminant loadings. This result is consistent with the hypothes is that contaminant loadings accelerated the collapse of the Pacific s ardine stock while it was under stress from severe overfishing. Althou gh many scientific questions about validation of models, mechanisms of action, and identity of specific deleterious contaminants remain to b e answered, the observed data are well described by the hypothesis of contaminant-mediated decline.