Bioenergetics of small pelagic fishes in upwelling systems: Relationship between fish condition, coastal ecosystem dynamics and fisheries

Coastal upwelling ecosystems provide the bulk of the world's fishery yields, but the biochemical ecology of the species that make up these fisheries has, surprisingly, been ignored. Biochemical indicators can provide a mechanistic, ecosystem-based link between population and ecosystem dynamics. Here we investigated long-term, inter-annual changes in the proximate composition and energetic condition of European sardine Sardina pilchardus and its relationship with oceanographic conditions in the Western Iberian Upwelling Ecosystem. Energy density (ED) ranged between 4.0 and 14.2 kJ g-1, and the seasonal cycle largely determined temporal variability, explaining >80% of the observed variation. ED variations were also closely linked with water (total R2 = 99.0% in whole body; total R2 = 95.0% in muscle) and lipid dynamics (total R2 = 99.6% in whole body; total R2 = 92.5% in muscle). After adjusting for seasonality (rED) and restricting the temporal analysis to the end of the feeding period (August to October), spring/early-summer oceanographic conditions explained 67% of the late-summer energetic peak. Interestingly, the sardine rED peak in year (t) explained >54.4% of the variation in the annual catches of year (t + 1), indicating that adult energetic condition during spawning is partially translated into the fishery through parental effects in recruitment strength. Our results support earlier findings indicating that sardine population dynamics seem to be controlled by bottom-up effects, but the linkages between population dynamics and patterns in environmental variability via physiological condition seem to have previously been overlooked. We also provide empirical evidence that biochemical assessments during critical periods of the life-cycle of fish are essential in understanding the population dynamics of coastal upwelling ecosystems and in developing a more solid basis for stock management and conservation.