Inshore marine resources of the reefs and lagoons are harvested mainly for subsistence. The FSM's exclusive economic zone covers some 2.6 million sq. km (1 million sq. mi) of ocean which contain the world's most productive tuna fishing grounds. Although the FSM now has sole ownership of tuna stocks capable of a sustained yield of well over 100,000 tons per year, there is virtually no national participation in its exploitation. The total catch in 2000 was 27,974 tons, including 19,192 tons of skipjack tuna, 6,384 tons of yellowfin tuna, and 1,043 tons of bigeye tuna. The tuna catch is valued at about $200 million annually. The Micronesian Maritime Authority and the National Fisheries Corporation assist in the development and promotion of commercial fisheries. Pohnpei and Kosroe have embarked on the construction of cold storage and tuna processing plants, and the Yap Fishing Corporation began upgrading its fleet. Total fisheries exports were valued at $620,000 in 2000.