Trophic links of Atlantic Bluefin tuna (Thunnus thynnus L.) inferred by fatty acid signatures

• FATMs from Bluefin tuna fat inferred trophic links showing yearly variability.
• Weight, gonad and fat indices accounted for 13.4% of total variation.
• Body weight was positively correlated with carnivory and high trophic position markers.
• The main source of variation was due to segregation of individuals.
• Most fish showed FA profiles of temperate and subtropical Atlantic ecosystems.

Fatty acid profiles were obtained from perigonadal fat of 98 adult Atlantic Bluefin tuna sampled from 2008 to 2010 at their confluence near the Gibraltar Strait as a consequence of their reproductive migration to the Mediterranean. Ten additional individuals caught, at the same season, off the Canary Islands, a place where no sexual migratory confluence occurred, were also sampled for their fatty acid signatures. Gender was not significant in explaining differences in fatty acids, and other biological traits such as weight, gonad index and fat/gonad ratio all together only accounted for 13.4% of total variation. Body weight was the more relevant factor and showed maximum positive correlation with 18:1n-9 and the 22:6n-3/20:5n-3 ratio (as carnivoy and higher trophic position markers), and maximum negative correlation with the flagellate marker fatty acid, 18:4n-3. Multivariate analysis of fatty acid trophic markers revealed a main source of data variation (66.9%) due to segregation of individuals in which part of the tuna population showed signatures characteristic of trophic resources from high latitude Atlantic ecosystems as revealed by elevated contents of the marker fatty acids, 20:1n-9 and 22:1n-11. The vast majority of tuna individuals were characterized by fatty acid profiles enriched in n-3 polyunsaturated fatty acids and more associated to temperate and subtropical Atlantic ecosystems in which haptophyte/dinophyte markers prevailed over those for diatoms at the base of their corresponding food webs. Fatty acid profiles of tuna from the Canary Islands were less dispersed than those caught at the Gibraltar Strait, reinforcing the assumption of the possible tuna confluence from different trophic grounds in this zone.