Surplus production, variability, and climate change in the great sardine and anchovy fisheries

Abstract

We used fishery and survey data to calculate annual surplus production (ASP) and instantaneous surplus
\nproduction rates (ISPR) for eight anchovy and nine sardine stocks. In addition, we calculated ASP per unit spawning
\narea for six anchovy and six sardine stocks. Median ASP was highest for stocks with highest median biomass (mostly
\nanchovies), and ASP was typically about 16% of stock biomass. ASP was often negative, more frequently for
\nanchovies (36% of years) than for sardines (17% of years). ISPR was less variable for sardines and autocorrelated for
\nlonger-lived stocks (mostly sardines). Strong biomass increases tended to be preceded by short, abrupt increases in
\nISPR, and declines were pronounced when catches exceeded ASP for 5 years or more. The longest “runs” of positive
\nand negative production were 21 and 4 years for sardine off Japan, 10 and 3 years for sardine off California, 8 and 2
\nyears for anchovy off Peru, and 4 and 3 years for anchovy off California. ISPR is more sensitive to environmental
\nchanges than catch, biomass, or ASP and appear to be better for identifying environmentally induced regime shifts.
\nLong time series show evidence of density-dependent effects on ASP in anchovies and sardines, but environmentally
\ninduced variation appears to dominate.