MILBRIDGE, Maine — At the Milbridge town Marina Friday morning, Linden Perry bailed water from an old wooden skiff to ready it to fetch his lobster boat from its mooring in the Narraguagus River. The aging fisherman exchanged a few bits of conversation with James Robertson about outboard motors.

Robertson’s boat already was at the pier, and he was getting his vessel ready to go out into Narraguagus Bay and beyond. Unlike Perry’s work boat, the Captain Cole, Robertson’s gleaming, spotless Kandi Leigh would not be hauling any lobster traps. Robertson was getting his boat ready to take out a small group of tourists on an excursion.

Roberton is a fisherman — some of the time. But when he is not diving for scallops or urchins in the winter, he is fishing for tourists and offering them one of several types of short cruises on the Kandi Leigh.

He is proof that fishermen can develop add-on businesses catering to the many tourists who visit Maine each summer, as well as Maine residents, although it’s not for everyone.

There are other fishermen who operate similar ventures, including Stefanie Alley, a lobster fisherman from Islesford on Little Cranberry Island, south of Mount Desert Island.

Robertson, 41, used to be a lobster fisherman, too. He grew up in — and still lives in — Harrington. He inadvertently lost his license when the Department of Marine Resources changed to a system that required fishermen to renew their licenses annually in the mid-1990s. Robertson would have been required to apprentice again on another fisherman’s boat, but by then he was not interested in working for someone else. He continued to dive for urchins and scallops in the winter and dug worms and clams during the summer.

As he considered his options, he eventually hit on the idea of starting a tourist-related business to provide brief excursions on a lobster boat or to see lighthouses, sea birds or other wildlife, or scenic coastal areas. Robertson found there was a substantial market for people who want to take a boat tour to see puffins and other birds.

He launched the tour business in 2001, starting with cruises to see puffins and other sea birds on Petit Manan Island off the coast of Steuben; the tiny island is part of the Petit Manan National Wildlife Refuge and also is home to Petit Manan Light, the second-tallest lighthouse in Maine.

He blazed a trail in the region, according to Robertson. “There was nobody doing what I was thinking of doing at the time,” he said while discussing his business at his home on Thursday.

“It was really slow getting started,” recalled Robertson. “I had to let the business lose money,” he said, while he earned his living from fishing and digging clams and worms.

His business, Robertson Sea Tours and Adventures, has grown. Now he offers several types of cruises, including one that features a lobster bake on an island, and also private charters. Robertson also contracts with another boat captain who takes customers out for whale-watching cruises. The tour business accounts for the majority of his income, he said — 60-65 percent.

“Come June, I’m completely swamped,” said Robertson.

Alley, 62, started a tour business in 2005 that supplements her income from lobstering. She averages from five to eight lobster boat cruises per week and fits them around her lobster fishing schedule. Like Robertson, she is set up to carry no more than six passengers.

Alley was a presenter at a workshop in Machias last winter to provide information to fishermen about how they could get involved in the tourism industry. It was one of several workshops — others were held in Portland and Belfast — conducted by the Maine Sea Grant College Program. Natalie Springuel, a Maine Sea Grant liaison to the coastal community development program of the National Sea Grant Network who works out of the College of the Atlantic in Bar Harbor, is another source for fisherman or others interested in starting a business that provides tour-type services to tourists.

Robertson and Alley are Coast Guard certified and have a captain’s license. Their boats are certified to carry up to six passengers and must be equipped with certain safety equipment, although Robertson described the investment as “fairly minimal.” They also have insurance for carrying passengers.

Robertson markets his business a variety of ways. “It’s a good mix,” he said. “We have a good Web presence. We’re really active in social media,” such as Facebook and Twitter. He also distributes brochures at various places in the region. He gets business from referrals, too, such as from innkeepers.

Angus and Cheryl Day learned about Robertson’s tour business through the TripAdvisor website. They joined Robertson for a puffin-watching cruise with four other people, leaving from Milbridge about 9 a.m. Friday.

The Days, from Fort Collins, Colorado, were visiting in Maine for 10 days. They enjoy nature-related tours and activities, explained Day. His wife noted that “every review” for Robertson on TripAdvisor was positive. They considered other, similar cruises out of Bar Harbor, but she desired a smaller boat with fewer people.

Alley, who discussed her tour business by phone Friday while attending a church conference in Rhode Island, gets most of her customers by word of mouth, although she distributes brochures and also has a presence on the town’s website.

A business that serves tourists is not for everyone, observed Robertson. “You have to be able to talk to people and entertain them … Not everybody wants to do that.”

Robertson was circumspect about recommending a tourist-related venture as a secondary business for other fishermen. “Because it’s really a commitment,” he noted, and lobster fishing is a full-time job. A tour business may have appeal to someone who wants to exit the fishing industry, he said, or as a supplement to someone who wants to scale back their fishing operations. “It all depends on what level you want to be at,” added Robertson, who noted that he has a family to support.

Alley offered a similar assessment. Whether other fishermen would want to have a tourism-related business would depend on “what they like to do,” said Alley. Some fishermen want to focus on building up their lobster business, she noted — adding more traps, perhaps getting a bigger boat.

Both Robertson and Alley have found another reason for providing excursions.

“It’s rewarding in the sense that people rave about it,” said Robertson. “It’s the time of their lives. They see things they would never never see anywhere else.”

For Alley, “It was an opportunity to meet people and show people a way of life. I like that part.”