Recognized by his brown, leather hat, worn smooth by decades of fishing in salt air on Island shores, Mike Cassidy is an anchor of the Martha’s Vineyard Striped Bass and Bluefish Derby. Known by the Derby Hall of Fame as “the derby’s unsung hero,” Mr. Cassidy has volunteered for the venerable saltwater competition for more than 40 years.

Unlike most derby’s longtimers, Mr. Cassidy did not grow up casting his line into Island waters. Washing ashore 43 years ago, he is a relative newcomer.

Born the third of 10 children, Mr. Cassidy grew up in an 880-square foot house in Norwood. His father, a factory worker, spent his rare weekends off fishing, bringing each of his five sons along. Despite experiencing violent seasickness as a child, Mr. Cassidy said he never missed his turn catching haddock and cod in the waters around Boston. He first visited the Island in 1978 from his home in Walpole, while on a short-term contract to paint six houses on Mattakesett Way in Edgartown.

That summer, he watched an angler catch a striped bass on South Beach and was hooked. Reeling in his own 39-pound “striper” on his first night fishing South Beach, Mr. Cassidy fell in love with the Island. He returned a year later in pursuit of a full-time painting contract and thoughts of creating a new life on the Vineyard. But when his wife got cold feet about the transition, Mr. Cassidy spent the summer commuting to the Island for painting jobs.

The following year, the family — including three children ages seven, five and two — made a permanent leap across the Vineyard Sound. They packed up their pop-up tent trailer and spent the summer living at the Martha’s Vineyard Family Campground.

Mr. Cassidy competed in his first derby in 1980 and was head of the derby committee from 1992-1994. — Ray Ewing

Today, at 72 years old, Mr. Cassidy still works as a painting contractor, running the same business that first brought him to the Island.

“Every time I go up a 36-foot ladder, I can hear my mother saying ‘Michael, get down from there!’” Mr. Cassidy said, his typically soft timbre giving way to an imitation of his mother’s voice. “I started climbing trees when I was 10 years old and I still like to climb.”

In the fall of 1980, Mr. Cassidy happened upon the derby in full swing and registered to compete. Making his way to the dock that would soon become his second home for 35 days each year, Mr. Cassidy met longtime filetmaster John Crews “knees-deep in bluefish.”

Mr. Cassidy volunteered to help filet, but the derby legend, in what Mr. Cassidy called his “usual dryness,” told the eager newcomer, “I got no time to teach tonight.”

Returning night after night, Mr. Cassidy finally found Mr. Crews with a free moment and he soon became a regular volunteer at the filet station, preparing hundreds of thousands of pounds of fish over the decades to be donated to the Island’s elderly population.

In 1987, Mr. Cassidy was invited to join the derby committee, which he chaired from 1992 to 1994. He took a step back from the position after two years because he believes that “if you don’t know how to follow, you don’t know how to lead.”

Thirty six years later, Mr. Cassidy is one of the derby’s living legends. But unlike many other big names in the derby, he insists that any notoriety he receives is not because of his talents as an angler. He cannot remember a time when he held a spot on the leaderboard.

“I may hold the derby record for the person who’s caught the most bait and the least amount of fish,” he said of the mackerel he often reels in for other anglers to use on their own lures.

Despite his humility, Mr. Cassidy is a force while fishing. He participates in the competition each year, reeling in false albacore, bluefish, bonito and striped bass (when it was still a part of the derby). But landing a fish is not the goal, he said.

“It’s that initial feel — that initial strike,” he said. “It’s the not knowing what’s on the end of the line.”

It is also about the people who migrate to the Island each fall and the committed community that keeps the tournament afloat, he said.

“It’s only been 24 hours, and I already know it’s going to be a good derby,” Mr. Cassidy said during the second morning’s weigh-in of this year’s derby. “Not because of the fish that came through last night, but because of the people who came through.”

Mr. Cassidy is also proud of the millions of dollars in scholarships the derby has provided to Island high school graduates and the work he does with Cooper Gilkes, derby stalwart and owner of Coop’s Bait and Tackle, for the kid’s derby, which takes place this Sunday, beginning at 6 a.m. at the Oak Bluffs Steamship wharf.

“I believe that everyone should do some kind of community service,” he said. “This has been mine.”

In 2007, Mr. Cassidy’s daughter Samantha was diagnosed with lymphoma at age nine. During her 25 long months of treatment, the Make A Wish Foundation sent the Cassidy family to Ireland.

Last year, with his daughter healthy and with gratitude for the foundation, Mr. Cassidy sought a way to pay the kindness back. He organized a “fishing wish” with the foundation for 15-year-old Finn Sears of Ireland, whose ultimate wish was to “catch a big fish.” A group from the derby committee brought Finn to the Island and took him fishing on Chappaquiddick, where the boy reeled in a 165-pound brown shark.

“Be careful what you wish for,” Mr. Cassidy said to Finn when the young fisherman hauled his catch ashore.

In the future, Mr. Cassidy hopes to sponsor more trips for children who might not otherwise have the chance to fish. He also volunteers for the American Heroes Saltwater Challenge, which brings wounded veterans to the Island to fish every year.

The largest reward of volunteering for the derby, he said, is “the opportunity to be a part of something transformative for so many people.”

As the 78th derby continues, Mr. Cassidy said he will enjoy the long evenings at the Edgartown dock, watching Island anglers turn up with stories from their days in the surf and at sea, children drag in their first bluefish to be weighed in, and the stars illuminate the night sky in “a dome of magical light.”

“If we are living in a simulation, to whoever drew it up and put me here, I’d like to say thank you,” Mr. Cassidy said, his pale green eyes fixed on the morning fog rolling into Edgartown Harbor.