Cornwall is a hotspot for basking sharks and they first turn up here. The migration follows the coastline and passes Land's End in spring. They are attracted by the high plankton concentration.
The season for basking sharks usually starts in May and last until October. Actually, the best time is mid-May until mid-July. However, there is no guarantee to spot these sharks. In 2017 the best time was April until the beginning of May. In 2018 the first sighting of two sharks was at the end of April. In recent years, fewer basking sharks were spotted. In 2019 two basking sharks were already seen on March 12 which is pretty early.
Very important are good weather conditions, a sunny day and calm wind to spot them on the surface of the sea and for snorkeling with them as well. Book your trip at short notice. First, check if basking sharks are already around the coast.