Tsugaru Strait

Lore & Background

The Tsugaru Strait was named after the western part of Aomori Prefecture. Western maps prior to the 20th century referred to it as the Strait of Sangar. Japan's territorial waters extend only three nautical miles into the strait instead of the usual twelve, reportedly to allow nuclear-armed United States Navy warships and submarines to transit without violating Japan's prohibition against nuclear weapons. Despite this, the part considered international waters remains within Japan's exclusive economic zone, and the Seikan Tunnel is entirely under Japanese jurisdiction even though part is technically outside territorial waters.

Reader's Guide

The Tsugaru Strait holds strategic and ecological significance. Its reduced territorial waters limit facilitates transit by nuclear-armed vessels, reflecting post-war security arrangements. The strait is also a major zoogeographical boundary, Blakiston's Line, named after English explorer Thomas Blakiston, who observed that animals in Hokkaido were related to northern Asian species while those on Honshu were related to southern Asian species. The Seikan Tunnel, passing under the strait, connects Honshu and Hokkaido. The strait has also been the site of tragedy, such as the sinking of the ferry Tōya Maru in 1954, which killed 1,172 people. Ferry services continue to operate across the strait, and it is included in the Oceans Seven marathon swimming challenge.

Did You Know?

• The Tsugaru Strait was referred to as the Strait of Sangar on Western maps prior to the 20th century.
• Japan's territorial waters in the strait extend only three nautical miles, reportedly to allow nuclear-armed U.S. Navy vessels to transit.
• The Seikan Tunnel passes under the strait at its narrowest point, 12.1 miles between Tappi Misaki and Shirakami Misaki.
• The strait is the location of Blakiston's Line, a zoogeographical boundary based on animal species differences between Hokkaido and Honshu.