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The Japanese coast guard says its patrol boats have been pushing back hundreds of North Korean boats trying to poach in fishing grounds rich with squid off Japan's northern coast.

Coast Guard officials said Tuesday they have forced more than 300 North Korean boats out of Japan's exclusive economic zone near Yamatotai since May.

The patrol boats used water cannons on 50 North Korean boats that ignored warnings.

Coast Guard footage obtained Tuesday showed North Korean crewmen on a wooden boat abandon a fishing rope after being sprayed water.

Japanese authorities have stepped up patrols in the area as North Korean poaching has surged in recent years.

Experts say Pyongyang's campaign to boost fish harvests has increased poaching by North Korean boats.