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
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AuthorsCarrera, P.(Pilar); González-Nuevo, G.(Gonzalo); Nogueira, E. (Enrique); Santos, M.B.(María Begoña); Riveiro, I. (Isabel); Bode, A.(Antonio)
The trophic position of sardine (Sardina pilchardus) in spring was determined from the analysis of the natural abundance of stable nitrogen isotopes in the southern Bay of Biscay between 1998 and 2014. Mesozooplankton (200-500µm) was employed as the reference baseline, as its isotopic signature tracked the seasonal development of phytoplankton blooms. Two methods for estimating trophic position were compared. Scaling the isotopic enrichment per trophic level to the isotopic signature of the reference baseline produced lower trophic position estimates than those using the traditional assumption of a constant enrichment per trophic level. Indeed, the studied sardine population is placed as a mid trophic level consuming prey near the base of the food web. Zonal averages of trophic position increased with decreasing size of the sardine stock and increasing values of the upwelling index, suggesting the interaction of trophic relationships and population dynamics. The effects of changes in the ...
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