Turkish Straits
The Bosphorus and Dardanelles under the Montreux Convention, the Turkish national traffic regulation, and the IMO routeing rules that sit alongside both.
The Turkish Straits comprise the Istanbul Strait at 17 nautical miles, the Marmara Sea at 110 and the Canakkale Strait at 37, a total of 164 nautical miles between the Black Sea and the Aegean. They are the outlet for Russian, Kazakh and Romanian crude and grain, and combined oil flows through them rose from 6.9 million barrels per day in 2023 to 7.4 million in the first half of 2025, the only major chokepoint in the series to gain traffic through the Red Sea crisis.
Passage is governed by the Convention Regarding the Regime of the Straits, signed at Montreux on 20 July 1936, which UNCLOS Article 35(c) preserves and to which Turkey remains party while not being party to UNCLOS itself. Montreux gives merchant vessels complete freedom of transit in peacetime and caps charges at the Annex I service tariff. The traffic-management powers exercised in practice come from Turkish national law rather than from Montreux.
The Mediterranean SECA ends at the Dardanelles entrance, on the Strait of Canakkale line from Mehmetcik Burnu to Kumkale Burnu, so the Straits and the Sea of Marmara are outside it.
The full article will cover the Convention’s merchant and warship regimes, the national traffic regulation of 2019 and its visibility rules, IMO Assembly Resolution A.827(19), and the practical transit conditions.