Two of the white sharks were tagged in Northern California and the rest were tagged off Baja California, said marine biologist Michael Domeier, president of the institute. The app coincides with a National Geographic Channel documentary "Expedition Great White", which aired last year. Despite the small sample size, Domeier said Santa Cruz ocean users might find the app useful in late summer to get an idea when the bulk of adult white sharks return. "You should not use the app to know where and when to go surfing," said Domeier. "But you can use it to know when they're in coastal waters and when they're not."