Abstract
We document that Atlantic bluefin tuna (BFT) began making a comeback from 2012 onwards into Norwegian waters, after several decades of absence, in parallel with an overall increased abundance recorded for eastern BFT. This study explores the distribution, biology and ecology of BFT reestablishing in Norwegian waters. We analyzed commercial catch and bycatch data including biological data on weight, length and age of BFT from 2016–2018. Predominantly larger (overall range in catches: 120−465 kg in weight and 184−297 cm in straight fork length (SFL)) adult individuals between 6 and 14 years old have recently started to revisit Norwegian waters. Numerous recently documented BFT observations were reported in this study, and a significant increase was detected from 2012 (n = 1) to 2018 (n = 105) (p < 0.01). Schools of BFT were observed predominantly from June to December, including the northernmost registered observation in history recorded at 76.2 °N in September 2018. Atlantic bluefin tuna has now reestablished and has shown a positive comeback to its historical migration patterns in Norwegian waters, where it has expanded its feeding areas towards the north.
Highlights
Atlantic bluefin tuna (BFT) (Thunnus thynnus) is the largest of all tuna species and is highly migratory (Fromentin and Powers, 2005)
Numerous recently documented BFT observations were reported in this study, and a significant increase was detected from 2012 (n = 1) to 2018 (n = 105) (p < 0.01)
Min mean max min mean max min mean max Bluefin tuna has reestablished in Norway and is exhibiting its historical migration patterns in Norwegian waters in recent years, after being absent for decades
Summary
Atlantic bluefin tuna (BFT) (Thunnus thynnus) is the largest of all tuna species and is highly migratory (Fromentin and Powers, 2005). It may reach 3.2 m in length, weigh more than 700 kg (Cort et al, 2013). Bluefin tuna has probably been feeding along the Norwegian coastline and in offshore waters for thousands of years (Tangen, 1999; Eidshaug and Sauvage, 2016; Nøttestad et al, 2017), due to the high abundance of nutrient-rich schooling prey species such as mackerel (Scomber scombrus), herring (Clupea harengus), blue whiting (Micromesistius poutassou), and lesser sandeel (Ammodytes marinus) found there (Tangen, 1999; Nøttestad et al, 2017; ICES, 2019). BFT visited Norwegian waters from early July until late October to feed
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