Long-term changes in maturation of sardine, Sardina pilchardus, in Portuguese waters

Long-term changes in sardine maturation were described using samples collected from landings off the western Portuguese coast since 1947. Estimates of the length at 50% maturity (L50) were calculated in 44 years of the study period and proved to be good proxies of the maturation length of first-year spawners (Lp50 of age 0-1 fish). Sardine probability of maturing at a given length declined from the early 1950s to the late 1960s, corresponding to an increase of ca. 2 cm in both L50 and Lp50. This trend reversed in the early 1970s and halted in the early to mid-1990s. The tendency for sardine to mature at a lower length was positively correlated with improved body condition in the growing season preceding maturation. Long-term trends in sardine maturation and body condition were parallel to trends in sea surface temperature reported in the literature. The results suggest that maturation at a lower size is directly influenced by increased temperature, and that higher temperatures improve body condition through increased feeding efficiency or a combination of both. We found no evidence that fishing intensity has contributed to long-term changes in sardine maturation.