Long-term variations in Ibero-Atlantic sardine (Sardina pilchardus) population dynamics: Relation to environmental conditions and exploitation history

In the current work we modeled the relationship between global atmospheric indices, seasonal sea surface temperature and coastal upwelling on the recruitment of the Ibero-Atlantic sardine. To study long-term Ibero-Atlantic sardine population dynamics a historical recruitment index (HRI) was developed from 1947 to 2012, for the Portuguese west coast, the main recruitment area of the Ibero-Atlantic sardine stock. HRI was calculated as the number of individuals ≤16.0 cm total length per landed kg using length and weight distribution data from purse-seine fleet landings. Recruitment periodicity changed after the late 1960s from 2-3 years to 4 years cycles. Atlantic Multidecadal Oscillation (AMO), summer North Atlantic Oscillation (NAO), summer sea surface temperatures (SST) and winter upwelling were significantly related with recruitment, explaining 45.9% of recruitment variability in the generalized additive model. Possible mechanisms leading to those relationships were discussed. A complex two-way relationship between the sardine exploitation and recruitment appears to exist. High recruitments allowed the increase in total landings in the following years but high exploitation periods may have also led to a decrease of the population potential productivity in the subsequent years.