Russian authorities have confirmed that a Japanese fishing boat they seized Wednesday while fishing in waters off Russian-held, Japanese-claimed islands under a bilateral agreement, had violated rules under the accord.

The border security agency from Sakhalin in Russia's Far East, which effectively administers the disputed islands, said Thursday they have found 714 kilograms of rays on board the Shoyo Maru No. 68, although the catch was not declared in the ship's logbook as required.

The agency has commenced an investigation for administrative proceedings based on Russian law.

The captain of the 29-ton boat, which belongs to a fishery cooperative based in Hokkaido's Nemuro city, is expected to face disciplinary action.

(Supplied photo shows Shoyo Maru No. 68.)
[Photo courtesy of the Russian border security agency]

"From a humanitarian perspective as well, we will appeal to Russia to let (the boat) return as soon as possible," Chief Cabinet Secretary Yoshihide Suga said at a press conference in Tokyo on Thursday.

The boat, with six crew members, was inspected on Wednesday evening by Russian authorities in the country's claimed exclusive economic zone before being taken to Furukamappu, known as Yuzhno-Kurilsk in Russia, on Kunashiri Island. The island is one of the disputed islets called the Northern Territories in Japan and the Southern Kurils in Russia.

According to the Hokkaido government and fishery cooperative, onboard processing of flounder was banned from this year following an agreement made between Japan and Russia.

The fishery cooperative has claimed its boat, which had been carrying headless Kamchatka flounder, was seized by Russian authorities for processing the fish onboard.

The incident follows last month's seizure of five Japanese fishing boats, also from Nemuro, by the Russian border patrol authorities. The vessels and their 24 crew members were released after paying a fine.

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