The sharks, the world’s second largest fish, after the whale shark, were sighted off the west coast along with the dolphins.
Oban company Basking Shark Scotland tracked them after a tip-off from fishermen that the fish had returned to their summer haunt.
Owner Shane Wasik took advantage of a settled weather forecast to go shark spotting with the company’s head guide, Luke Saddler.
The pair had the bonus of seeing scores of dolphins and minke whales.
Mr Wasik said they had passed a pod of more than 100 dolphins, within a mile, as they searched around the islands of the Inner Hebrides, where they found the sharks.
He said: “Four individuals were sighted, the largest at least eight metres (26 feet) long and male.”
The marine biologist added: “It was really exciting to see the basking sharks back in our waters, and great to have some large individuals.
“They undertake such huge migrations, it’s such a privilege to see them every summer.
“We’re looking forward to the shark season ahead and pushing on with our work with them.”
He added: “Basking sharks arrive in UK waters around spring, with many having completed a large offshore migration over winter. Usually they arrival between April and June.
“However, with the settled and sunny weather the Western Isles have had and the resulting plankton bloom, it was no surprise that sharks had arrived to take advantage of this food source.”
Satellite tagging has confirmed that basking sharks move thousands of miles during the winter in search of plankton blooms.
In 2007 a female basking shark was tracked for 88 days, swimming from the UK to Newfoundland, Canada, while a 2009 study tagged 25 sharks off the coast of Cape Cod in the US, with some crossing the Equator to reach Brazil and one spending a month near the mouth of the Amazon river.
The first sharks of the season to be recorded in Scotland are now sharing the west coast waters with an abundance of dolphins.
Mr Wasik said: “We started counting the first groups and got to around 60, then the second and third groups were just as big, so there were well over 100 dolphins.”
Ferry passengers travelling from Mull to Oban on Thursday also reported seeing a mass of dolphins, with the ship’s sonar equipment picking up images of 50.