Management of forage fish is challenged by the apparent sensitivity of forage fish to the environment and by the unpredictable nature of shifts in productivity. One of the best-known relationships between forage fish and their environment is the phenomenon of asynchrony in sardine (Sardinops spp.) and anchovy (Engraulis spp.) populations, with many documented cases of species replacements and / or asynchronous fluctuations between the two species. However, it is unclear whether these patterns are consistent across large marine ecosystems (LMEs) where both species occur. Differences in the dynamics of landings, biomass, and recruitment may indicate differences in the causes or effects of asynchrony. Here we evaluate two key components of sardine and anchovy dynamics: the degree of asynchrony (covariance in abundance) and replaceability (are peak catches or biomass levels similar between species). We assessed asynchrony and replaceability in landings, biomass, and recruitment time series for sardine and anchovy worldwide.
Results/Conclusions
We found variations in asynchrony and replaceability between LMEs. Both landings and biomass tended to be consistently dominated by one of the two forage species, indicating that fisheries and predators cannot rely on a consistent amount of forage resource during years when productivity is low for the dominant species. Dynamics of sardine and anchovy landings, biomass, and recruitment were not consistently asynchronous across LMEs. We hypothesize that the mechanisms causing these asynchronous dynamics vary spatially, and that our ability to detect asynchrony depends on the length of the observed time series.