Leaders at the Martha’s Vineyard Striped Bass and Bluefish Derby confirmed Tuesday that a fish had been disqualified based on evidence that derby rules had been broken.

The 36.42-pound striped bass led the shore bass division for much of the tournament, but was knocked off the leader board on the final morning of the tournament by a larger fish.

The disqualified fish was weighed in by a nine-year-old boy from Chilmark on Oct. 12. His father, Lev Wlodyka, is a well-known fisherman who has often been on the leaderboard with large fish.

“We have sufficient evidence to realize a rule was violated,” derby chairman Ed Jerome told the Gazette Tuesday. He said he could not provide details except to say that the derby committee will consider evidence and make a decision about whether to impose sanctions as a result of the violation. The derby executive committee decided to disqualify the fish in the final hours of the competition Saturday evening.

Internal deliberations among the derby committee are kept private, Mr. Jerome said.

He also said the derby, which concluded its 71st year last weekend, is a well respected tournament, and the rare instance of rules violations are an unpleasant part of the job for volunteer committee members.

“It’s the last thing we want to do with the derby,” Mr. Jerome said. “The derby is fun to operate and to be part of. This is the one singular thing we totally dislike.”