Cycles and trends in the Iberian sardine (Sardine pilchardus) stock and catch series and their relationship with the environment.

Abstract

The Iberian sardine ( Sardine pilchardus ) is a good example of the typical life strategy of small pelagic fish species around the world: short life span, fast growth and long spawning season, which in the case of the Iberian stock presents two peaks (in winter and spring). This life strategy makes new year classes ve ry dependent on the right environmental conditions to survive the early life stages. Egg and larval survival relies on the right oceanographic mechanisms, to ensure retention in favourable areas, and availability of food. Dispersal of eggs and larvae serio usly reduces their survival and decreases the chances of a good new year class. Because of this dependency on environmental conditions in early life, there is no relationship between the stock size (measured as SSB) and recruitment. Previous studies have e xplored the relationship between environmental variables, at large and local spatial scales, and sardine recruitment in the Galician and Portuguese sardine fishery but have faced two main analytical challenges: short time series and autocorrelated data. We carry out new analysis using statistical methods designed to cope with these challenges, including Dynamic factor Analysis and mixed modelling, to identify and characterise relationships between sardine populations (recruitment, spawning stock biomass, an d (to extend the time series) fishery landings in the area) and a series of global, regional and local environmental variables.