Otolith shape analysis as a tool for stock separation of albacore tuna feeding in the Northeast Atlantic

For management purposes, albacore tuna (Thunnus alalunga, Bonnaterre 1788) in the North Atlantic are considered to be from one homogenous stock. However, multiple lines of evidence suggest that there is some degree of stock complexity. In this study, the stock structure of North Atlantic albacore tuna is investigated using otolith shape analysis. Juvenile albacore tunas were collected from the commercial fishery in the Bay of Biscay region over a three-year period (2012-2014). Catches were concentrated in two main areas: within the Bay of Biscay (East) and off the western shelf edge (West). Otolith shape was defined using Elliptical Fourier analysis and was compared between albacore from these two catch locations using generalised canonical discriminant analysis. The results show significant differences in otolith shape between albacore from the Eastern and Western locations using Elliptical Fourier descriptors. The discriminant analysis and jack-knifed cross-validation classification correctly classified East and West samples with a success rate of 72% and 75% respectively. The results suggest that two components with distinct environmental life histories contribute to the fishery in the Northeast Atlantic. It also implies that albacore juveniles display some degree of fidelity to their feeding areas.