BOSTON (AP) – Regulators have abandoned a 2008 deadline and will give fishermen at least nine extra years to rebuild lobster stocks that mysteriously crashed in southeastern Massachusetts and Rhode Island.

The cause of the crash in the late 1990s and early 2000s is unknown, and regulators are uncertain exactly what steps can revive the stock without wiping out lobstermen’s businesses.

But the original 2008 deadline for rebuilding the stocks is now considered unreachable, and fisherman will have until at least 2017, and perhaps until 2022, to bring back the lobster numbers, according to new rules proposed by the Atlantic States Marine Fisheries Commission, which manages the stock.

Among the possible rebuilding steps: increasing the size of lobsters that can be kept, adjusting gear to allow more lobsters to escape, or catch quotas.

“It very difficult. When you don’t know the problem, it’s hard to cure it,” said Vito Calomo, a proxy for state Rep. Anthony Verga, D-Gloucester. Calomo is a member of the multi-state board that will vote on the final rules in May.

Lobster stocks are considered healthy in Georges Bank and the northern waters off Maine and Massachusetts.

But a lobster crash came off southeastern Massachusetts and Rhode Island after overfishing, an oil spill in the mid-1990s and a disfiguring shell disease, though scientists never named a single cause. Between 1999 and 2002, the catch dropped from roughly 8.2 million pounds to about 3.8 million pounds.

The crash was simultaneous with a massive die-off in Long Island Sound, which lobstermen later blamed in part on pesticides sprayed in New York and Connecticut.

Recovery has been slow in both areas, which are part of the Southern New England lobster region. Estimates put the number of lobsters in the region at about 14 million, about 41 percent below regulators’ target of 23 million.

In its document outlining the proposed rules, the commission acknowledges it doesn’t know the reasons for the lobster decline or how much of a reduction in the catch is needed for stocks to recover.

Toni Kerns, a management plan coordinator with the commission, said regulators aren’t “completely flying blind” in devising rules because they work with lobster catch information and other data. But she said they are often forced to make decisions with extremely limited information.

With such uncertainty, the proposed rules lack specifics on how to help stocks recover, but instead lay out rebuilding timetables, and leave flexibility for regulators to try measures to help the stock.

Two of the proposed rules give fishermen until 2017 to reach the target for the lobster population, while two others give them until 2022.

The proposed rules also vary on the pace at which lobsterman must reduce their catch to a level that is considered safe for the long term health of the stock.

Two of the rules would require lobstermen to meet that level within two years. The others would give fishermen until 2017 or 2022, which would mean less immediate financial pain.

About 500 full and part-time lobstermen in the southeastern Massachusetts and Rhode Island area split 150,000 traps – down from 1.3 million permitted a few years ago, said Rhode Island lobsterman Lanny Dellinger, president of the Rhode Island Lobstermen’s Association.

Dellinger, who fishes out of Newport, said a recent survey showed a small increase in the number of lobsters in his area, and he’s hopeful the unexplained decline was just part of a natural cycle that’s on its way back up.

“I think we’ve made it through the hard time,” he said.