Sardine and anchovy can exhibit dramatic decadal-scale shifts in abundance in
response to climate variability. Sharpe declines of these populations entail particularly
serious commercial and ecological consequences in eastern boundary current ecosystems,
where they sustain major world fisheries and provide the forage for a broad variety of
predators. Understanding the mechanisms and environmental forcing that drive the
observed fish variability remains a challenging problem. The modelling study presented
here provides an approach that bridges a comprehensive database with an end-to-end
modelling framework enabling the investigation of the sources of variability of sardine and
anchovy in the Canary Current System. Different biological traits and behaviour
prescribed for sardine and anchovy gave rise to different distribution and displacements of
the populations, but to a rather synchronous variability in terms of abundance and biomass,
in qualitative agreement with historical landing records. Analysis of years with
anomalously high increase and decline of the adult population points to food availability
(instead of temperature or other environmental drivers) as the main environmental factor
determining recruitment for both sardine (via spawning and survival of feeding age-0
individuals) and anchovy (via survival of feeding age-0). Consistent with this, the two
species thrive under enhanced upwelling-favourable winds, but only up to some threshold
of the wind velocity beyond which larval drift mortality exceeds the positive effect of the
extra food supply. Based on the analysis of the simulation, we found that anchovy larvae are
particularly vulnerable to enhanced wind-driven advection, and as such do better with
more moderate upwelling than sardines.
