BOSTON – A plan to aid the fishing industry by creating a new class of fishing days is lagging, say its authors, who worry it’s being thwarted by a rivalry between Maine and Massachusetts.

“I don’t know the history of Maine versus Massachusetts, but [the rivalry] is alive and well,” said Jackie Odell, executive director of the Gloucester-based Northeast Seafood Coalition.

The coalition’s plan creates so-called “B Days,” on which fishermen can target only healthy stocks, such as haddock. The extra days offset losses for fishermen absorbing a 24 percent cut in regular fishing days, which is intended to protect vulnerable fish, such as cod.

The plan was approved overwhelmingly by the New England Fishery Management Council last fall as part of a slate of tough new restrictions to stop overfishing, called Amendment 13, scheduled to take effect in May.

From the start, Maine fishermen protested the “B Day” plan, saying the healthy fish stocks off southern New England were so far away they would waste too much of their allotted time in transit. They said fishermen would abandon Maine en masse to move to ports closer to the healthy stocks.

The disagreement awakened talk of occasional disputes between two states that share fishing grounds and history. Maine was part of Massachusetts until it broke away in 1820.