Stock dynamic of the Iberian sardine (Sardina pilchardus Walb.) and its implication on the fishery off Galicia (NW Spain)

Abstract

The recent failure of sardine catches off Galicia (NW Spain), an area where landings reached up to 100 thousand tonnes only a few years ago, may be explained by two possible hypotheses. The "depletion" hypothesis states that diminishing sardine catches were due to a decrease in stock biomass resulting from a combination of reduced recruitment and increased fishing mortality. The "change in distribution" hypothesis states that catch failure was due to a change in the distribution of the stock owing to environmental changes. Available information, based on direct observations from acoustic and ichthyplankton surveys and the fishery, was analysed. When the stock size is high, the spawning area of the sardine extends offshore in the Cantabrian Sea, and spreads along the continental shelf off northern Portugal. Moreover, adult fish undertake feeding migration towards Galician waters. This spawning behaviour results in a recruitment located mainly off Portugal. Low stock size causes a shrinkage in the distribution area throughout coastal waters and in the Cantabrian Sea, reaching the inner part of the Bay of Biscay. This process also affects the migration range and favours a higher retention in coastal waters of the early life stages (from eggs to recruits), which remain primarily in the same area where they were hatched. The lack of sardine in Galicia may be explained by a depletion process which affects both the feeding migration of adult fish and the recruitment occurrence off southern Galicia. This paper also analyses the dynamics of this stock in the context of a metapopulation. Taking this concept into consideration, we also examined the influence of the dynamics of each sub-population and the environmental conditions that might affect the success of the recruitment.