Stomach content and stable isotope analyses reveal resource partitioning between juvenile bluefin tuna and Atlantic bonito in Alboran (SW Mediterranean)

Abstract

The Alboran Sea holds one of the highest biological productivity rates in the Mediterranean, and thus represents an important nursing area for pelagic fishes including tunas. Trophic interactions between sympatric populations of age-0 bluefin tuna (ABFT) and Atlantic bonito (BON) were investigated in Alboran by integrating stomach content analysis (SCA) and stable isotope analysis of bulk muscle (BSIA) and individual amino acids (AA-CSIA). BON and ABFT individuals were collected in the Bay of Malaga; additionally, ABFT were caught off Carboneras. SCA showed that BON fed only on teleost fishes, whereas ABFT diet also comprised invertebrates. We found significant dietary differences between groups using SCA and BSIA data. Low values of niche width estimated from SCA and BSIA indicate poor dietary diversity in the two sampling sites. There was no isotopic niche overlap between groups, which may indicate resource partitioning. Trophic positions (TP) estimated from SCA, BSIA and AA-CSIA place BON at higher TP than ABFT.