Bluefin tuna migration routes: when it passes the Iberian Peninsula and a world calendar

Bluefin tuna keep a timetable. Every year they run the same circuit, and whoever knows it knows where to be and when. What follows has been measured by the satellite tags of ICCAT's scientific programmes and of institutes such as the Spanish Institute of Oceanography or Norway's Institute of Marine Research. Dates are indicative: water temperature moves them a couple of weeks either way.

The eastern stock's cycle

• Winter: adults feed spread across the central and northern Atlantic.
• April to June: spawning migration into the Mediterranean. Fish tagged in the Balearics by Aranda and colleagues (2013) and those tagged in Norway (Nøttestad et al., 2024) cross the Strait of Gibraltar between mid-May and June. These are the inbound fish of the Cádiz almadraba traps.
• June and July: spawning in the Balearics, the Tyrrhenian and the eastern Mediterranean, peaking around the June solstice, when the water passes 19–20 °C.
• Late June to August: exit to the Atlantic, again through the Strait, and dispersal: Algarve and Bay of Biscay first, then Ireland, Iceland and Norway until October. One tag from the Balearic study surfaced off south-east Iceland on 30 September.
• Autumn: fattening in the north and return to the central Atlantic. A tuna tagged in Norway can be back in Norway the following year: site fidelity is high.

Calendar by Iberian area

• Strait, Tarifa and Cádiz: May–June (inbound) and July–August (outbound). Big fish, passing through, in current.
• Algarve: June to September, with fish leaving the Mediterranean and staying to feed.
• Balearics and Levante: June–July. Spawning ground, with the strictest rules: check before you go.
• Bay of Biscay and Galicia: July to October, tuna fattening after spawning. The highest length-weight ratios of the year are found here.
• Canary Islands: February to May, bluefin passing through; bigeye takes over in summer.
• Azores: April to June for bluefin; bigeye from May to October.

Tuna around the world

• United States (western stock): Cape Cod and New England from June to November, peaking in August and September; in winter they move down to North Carolina's Outer Banks, November to April.
• Canada: Prince Edward Island and Nova Scotia, July to October, with giants over 400 kg, almost all catch and release.
• Norway: August to October, in a recreational fishery tied to scientific tagging.
• Japan: here the species is the Pacific bluefin (Thunnus orientalis). It spawns from April to July between Taiwan and the Ryukyu Islands and in July–August in the Sea of Japan; at one year old, part of the juveniles cross 8,500 km to California and return years later to spawn (Kitagawa, University of Tokyo). Adults move north in summer and south in winter: the famous Oma tuna of the Tsugaru Strait are fished from summer to autumn, with the best fat as winter sets in.
• Australia and New Zealand: southern bluefin (T. maccoyii), February to June in Victoria and March to June in Tasmania.

With a date and an area you have half the job done. The other half, technique, is in trolling for tuna and popping and stickbaits.

Sources

• Aranda, G. et al. (2013). Spawning behaviour and post-spawning migration patterns of Atlantic bluefin tuna ascertained from satellite archival tags. PLOS ONE. Article
• Nøttestad, L. et al. (2024). Atlantic bluefin tuna tagged off Norway show extensive annual migrations… Proc. R. Soc. B. Article
• Kitagawa, T. (University of Tokyo), in GLOBERIDE Compass: the great migration of Pacific bluefin (Japanese).
• Aomori Fisheries Cooperative Federation: マグロ (Japanese).
• Victorian Fisheries Authority and Fishing Tasmania: southern bluefin seasons.
• Spanish Ministry of Agriculture, Fisheries and Food: recreational sea fishing.