Whale watching for gray whales on migration began in the 1970s. There is some shore-based whale watching from headlands along the coast highway but not as much as in California, and revenues are probably minimal. Ten whale-watching companies, using 41 boats, offer whale watching from five different ports. Gray whales can be seen on the northbound migration from November to December or on the southward from February to April. Depoe Bay is the centre for whale watching, with more than 95 precent of the state's whale-watching visitors. Other ports are Newport, Charleston and Garibaldi. Average cost is $20 US for a three-hour tour, though in Depoe Bay, it is possible to see whales for $7 US on a one-hour tour. In 1991, an estimated 100 000 people went whale watching on gray whale tours.