Food-web dynamics in the Portuguese continental shelf ecosystem between 1986 and 2017: Unravelling drivers of sardine decline

The Ecopath food web model that describes the Portuguese continental shelf ecosystem was fitted to available time series to investigate the ecosystem dynamics and decline of the Portuguese sardine stock. Our results showed that the Portuguese continental shelf ecosystem model is a good predictor of biomass and catch time-series trends for many species. Moreover, our results suggested that the main factors that drove the ecosystem dynamics were trophic interactions, fishing and environmental forcing (sea surface temperature). The same drivers were important in explaining sardine decline among which the largest contribution was observed when incorporating sea surface temperature forcing on adult sardine, followed by fishing. Moreover, sardine eggs predators (i.e., chub mackerel, horse mackerel and bogue) were emphasised as the most important among trophic interactions in explaining sardine trend between 1986 and 2017. Furthermore, a flow control hypothesis test, showed that model parametrization allows explaining sardine behaviour through wasp-waist control mechanism, characteristic for upwelling systems. This study represents an important step forward in understanding the changes that occurred in the Portuguese continental shelf ecosystem and provides helpful insights to explain Portuguese sardine decline.