ROCKLAND — Maine’s booming lobster industry has a big problem involving a little fish.

The state’s iconic lobster fishery is healthy, having set records for volume and value in 2016. But the fishery for herring, a small schooling fish that lobsters love to eat, is another story.

Herring is suddenly the second-most valuable fishery in the state, and Maine’s most valuable species of fish, bringing in $19 million at the docks in 2016. It’s also the most popular bait used in lobster traps, and the climb in value corresponds with demand from the hungry lobster fishery and a drop in catch of herring off New England.

Scientists and fishermen are trying to figure out why Maine’s Atlantic herring catch – the largest in the nation – has fallen from 103.5 million pounds in 2014 to 77.2 million last year. The per-pound price of the fish at the dock has gone up 56 percent since 2014, and that price is eventually borne by people who buy lobsters.

“The whole dynamic of the fishery has changed,” said Jeff Kaelin, who works in government relations for Lund’s Fisheries, which lands herring in Maine.

Kaelin, and others who work in and study the fishery, thinks climate and the way the government manages herring may have played a role in the decline of catch. Atlantic herring are managed via a quota system, and regulators have slashed the quota by more than 40 percent since the early 2000s.

Last year, herring were also difficult to catch far offshore, where they are typically caught in large amounts, but they were abundant closer to the New England coast. This led to a bait shortage, because fishermen are only allowed to catch a certain percentage of their quotas in inshore waters.

It also fueled speculation that warming waters are preventing herring, which like the cold, from going farther out to sea, where it is warmer. Graham Sherwood, a research scientist with the Gulf of Maine Research Institute in Portland, said it’s tough to say whether warming waters are actually keeping herring close to shore in the near term.

But long term, the much-documented warming off New England is bad for the fish, he said.

“They are a cold water species. Ten, 20, 30, 50 years, it may no longer be hospitable to herring,” Sherwood said.

Federal and interstate regulators are looking at different strategies for how to manage the herring shortage. No radical changes are planned imminently.

It’s all happening at a time when demand for herring is possibly greater than it has ever been. The U.S. lobster fishery, which is also centered in Maine, has exploded in recent years, growing from 81 million pounds nationwide in 2007 to more than 130 million pounds in Maine alone last year. Processed lobster products are growing in popularity, and the Asian market for live lobsters has broken wide open.

That growth has driven up demand for bait, said David Cousens, president of the Maine Lobstermen’s Association. The price of herring to fishermen grew from $30 to $40 per bushel last year, Cousens said. Fishermen also use other types of fish, such as redfish and menhaden, but herring remain the overwhelming favorite, he said.

“They’ve cut the quotas in half and we’re using twice as much bait as we used to,” he said. “It’s a huge problem.”