Is the recruitment a key biological process in the hypothetical NAO-Atlantic tunas relationships

In the recent past, it has been put forward that recruitment of the North Atlantic albacore, East Atlantic bluefin tuna and North Atlantic swordfish could be related to the North Atlantic Oscillation (NAO). In this document, the biological processes behind the NAO/recruitment relationship are further investigated. Then, the possible relationship between the East Atlantic bluefin tuna recruitment was re-investigated. The linear relationship appeared to be only due to the low frequency signal, both BFT recruitment and NAO displaying a pseudo-cyclic upward trend, but year-to-year fluctuations were not synchronous. The superposed epoch analysis, that was conducted to test for possible non-linear and non-monotonous relationship did not reveal any clear connection. In conclusion, it appears that the available data on BFT recruitment cannot support the hypothesis of an impact of the NAO on BFT recruitment. Spatially disaggregated data are needed to further investigate this hypothesis. Finally, we stressed the interest to explore other mechanisms, such as the influence of the NAO on spatial distribution, migration routes and catchability. RÉSUM