Bauer R. K., Forget Fabien, Fromentin J. M., Capello Manuela. (2020). Surfacing and vertical behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Mediterranean Sea : implications for aerial surveys. Ices Journal of Marine Science, 77 (5), p. 1979-1991. ISSN 1054-3139.
Titre du document
Surfacing and vertical behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Mediterranean Sea : implications for aerial surveys
Bauer R. K., Forget Fabien, Fromentin J. M., Capello Manuela
Source
Ices Journal of Marine Science, 2020,
77 (5), p. 1979-1991 ISSN 1054-3139
Atlantic bluefin tuna (Thunnus thynnus) (ABFT) frequently engage in surface basking and foraging behaviour that makes them detectable from afar. This behaviour is utilized for the development of fisheries-independent abundance indices based on aerial surveys, although changes in the surface-feeding dynamics of ABFT are not yet accounted for. We investigated the daytime surfacing behaviour of ABFT at different temporal and vertical resolutions based on 24 individuals (117-158 cm fork length), tagged with pop-up archival tags in the Gulf of Lion, NW-Mediterranean Sea between 2015 and 2016. The results suggest that ABFT remain usually <2 min continuously within the visible surface (0-1 m) during daytime. ABFT presence in the 0-1 and 0-20 m layers varied over time and between individuals but showed a seasonal decline towards autumn with the breakdown of thermal stratification. Furthermore, the rate of surfacing events was highly correlated with the time spent in the 0-20 m layer. Geolocation estimates confirm a strong site fidelity of ABFT during the aerial survey period (August-October) in the Gulf of Lion. Our results support the choice of the survey region and period, but related indices should account for the seasonality of ABFT surface behaviour [i.e. the time spent in the 0-20 m layer.
