2008, while the latter uses 35% of its output to fuel the Longyearbyen Power Station. Since 2007, there has not been any significant mining by the Russian state-owned Arktikugol in Barentsburg. The Gruve 7 mine is scheduled to shut down in 2025. There has been test drilling for petroleum on land, but these did not give satisfactory results for permanent operation. Norwegian authorities do not allow offshore petroleum activities for environmental reasons, and the land formerly test-drilled have been protected as natural reserves or national parks. In 2011, a 20-year plan to develop offshore oil and gas resources around Svalbard was announced. Svalbard has historically been a base for both whaling and fishing. Norway claimed a exclusive economic zone (EEZ) around Svalbard in 1977, with of internal waters and of EEZ. Norway retains a restrictive fisheries policy in the zone, and the claims are disputed by Russia. Tourism is focused on the environment and is centered on Longyearbyen. Activities include hiking, kayaking, walks through glacier caves, and snowmobile and dog-sled safari. Cruise ships generate a significant portion of the traffic, including both stops by offshore vessels and expeditionary cruises starting and ending in Svalbard. Traffic is strongly concentrated between March and August; overnight stays have quintupled from 1991 to 2008, when there were 93,000 overnight stays. Research on Svalbard centers on Longyearbyen and Ny-Ålesund, the most accessible areas in the high Arctic. The Svalbard Treaty grants permission for any nation to conduct research on Svalbard, resulting in the Polish Polar Station and the Chinese Arctic Yellow River Station, plus Russian facilities in Barentsburg. The University Centre in Svalbard in Longyearbyen offers undergraduate, graduate, and postgraduate courses to 350 students in various arctic sciences, particularly biology, geology, and geophysics. Courses are provided to supplement studies at mainland universities; there are no tuition fees and courses are held in English, with Norwegian and international students equally represented. The Svalbard Global Seed Vault is a seedbank to store seeds from as many of the world's crop varieties and their botanical wild relatives as possible. A cooperation between the government of Norway and the Global Crop Diversity Trust, the vault is cut into rock near Longyearbyen, keeping it at a natural and refrigerating the seeds to . The Svalbard Undersea Cable System is a fibre optic line from Svalbard to Harstad, needed for communicating with polar orbiting satellites through Svalbard Satellite Station and installations