Interspecific, ontogenetic and temporal variations in stable isotopes of small tuna species in the northeast Atlantic Ocean.

In order to study the trophic level of small tuna species and their contribution to the carbon flow in pelagic food webs, an analysis of carbon and nitrogen stable isotopes was carried out. The investigation was focused on four small tuna species (, , and ) commonly harvested in the northeast Atlantic Ocean. The isotope analysis showed how the results for are different from the rest of the species analysed, with a higher trophic level, similar to other major tuna species. The greatest niche overlap in δC and δN occurs among , and . and showed a size-dependent variability in δN, and in δC for . The small tuna exhibits the highest migration rates among various geographical areas in comparison to other small pelagic tunas, and the seasonal variability of isotope values in the area studied can be attributed to the incorporation of larger individuals with a higher lipid content. The results of this work provide new information on the ecological role played by small tuna in food webs, which is more complex and varied than currently thought. This knowledge is essential for a more effective management of fisheries.