Environmental and parental control of Pacific sardine (Sardinops sagax) recruitment

We confirm that sardine recruitment in the California Current, during the last three decades, mimics aspects of the environment in the North Pacific indicated by the Pacific Decadal Oscillation (PDO) index. The periods of stock increase and decrease followed consecutive years with positive and negative PDO values, respectively. During the warm periods, the average number of recruits per biomass was more than threefold higher than that during the cold periods. In addition to the environmental conditions experienced by the sardine larvae, we show that the variability in sardine recruitment is partially explained by the environmental conditions many months before the spawning season and the adult condition factor. We hypothesize that sardine have a metabolic deficit during spawning, so prior good feeding opportunities are necessary to increase both total fecundity and offspring robustness, to enhance both reproduction and survival, respectively. Our findings augment a century-old theory that the reproductive success of small pelagic fish is governed by the survival of the early life stages. The condition of each parent also matters. To predict sardine recruitment, we propose a dual-phase model based on seasonal PDO-based indices and a condition factor. The model identifies summer feeding seasons conducive to a good adult condition factor followed by spring-spawning seasons supportive of good larval retention and growth.