A trophic index for sardine (Sardina pilchardus) and its relationship to population abundance in the southern Bay of Biscay and adjacent waters of the NE Atlantic

摘要: Abstract The trophic position of sardine (Sardina pilchardus) in spring was determined from the analysis natural abundance stable nitrogen isotopes southern Bay Biscay between 1998 and 2014. Mesozooplankton (200–500 µm) employed as reference baseline, its isotopic signature tracked seasonal development phytoplankton blooms. Two methods for estimating were compared. Scaling enrichment per level to baseline produced lower estimates than those using traditional assumption a constant level. Indeed, studied population is placed mid consuming prey near base food web. Zonal averages increased with decreasing size stock increasing values upwelling index, suggesting interaction relationships dynamics. effects changes timing blooms release competition at low densities discussed potential factors causing an increase mean recent years. application scaled monitoring populations will facilitate comparison different studies provide new insights on regulating these populations.