Out of the bulging nylon net poured the residents of Frenchman Bay’s muddy floor: crabs, starfish, sea cucumbers, mystery fish with an alien look to them.

The catch filled the stern of Jon Carter’s boat with several inches of water and splashing aquatic life. Carter and his son, Shane, waded in quickly. As they scanned back and forth across the writhing deck, their gloved hands pulled out selected creatures and tossed them into a tank.

In a matter of minutes, the tank was filled with 35 skates and 18 long-horn sculpin — hardly appetizing, but exactly what Carter was looking for. The fish quickly made themselves at home in the live tank, hugging the bottom the way they would the ocean floor.

That, too, was what Carter wanted to see. It is his job to bring `em back alive.

For nine months a year, Carter catches conventional fare for the Bar Harbor market — lobster, scallops and occasionally shrimp.

But from June through August, Carter hauls fish only a scientist could love — dogfish, sculpin, skates. These odd-looking specimens go to the Mount Desert Island Biological Laboratory in Salsbury Cove, where they have been studied by biologists since 1921.

Carter has been fishing for the laboratory for more than 20 summers now, first as a crew member on one of the laboratory’s boats, then as skipper of its dogfish boat, and finally as the lab’s only supplier.

“I would say 95 percent of the investigators here are almost completely dependent on Jon Carter’s ability to catch fish,” said Don McCrimmon, associate director at the laboratory.

For years the investigators studied the whole fish. Then their search to understand the human kidney took them toward study of individual parts of the fish.

Now investigators at the laboratory are shifting their emphasis toward the developing science of molecular biology, using only the tiniest tissue samples. But none of this changes the basic supply needs of the laboratory: samples of Frenchman Bay’s indigenous population, alive and in good health.

“It’s conceivable we might need fewer samples in the future, but they will have to be in excellent condition,” McCrimmon said, adding that they will still need the fish fresh on a daily basis.

Carter has spent a lifetime learning to meet those specific needs. While he has it down to a science now, finding, catching and preserving the laboratory’s specimen’s has not always been easy.

“We used to put in 10 to 12 hours a day, seven days a week, just figuring out what to do,” he said.

“I learned right off in the beginning that the further out I go, the worse I do for what I want,” Carter said. The dogfish and skates that first attracted the laboratory to its site in Salsbury Cove are less plentiful now, but they still inhabit the waters off Bar Harbor and Gouldsboro.

Carter has also mastered the tricks of keeping the fish alive. First, instead of icing the fish, he puts them in a live tank, which he is still tinkering with to perfect circulation of the freshest, coolest ocean water.

Second, he has altered standard techniques for netting the fish. When dragging for skates, sculpin and flounder, he uses a shorter net, and leaves it on the bottom for shorter periods of time. And when he reels the net onboard — which he does more slowly than he might otherwise — Carter makes sure that the fish spend a minimum amount of time out of water.

“When they come aboard, we don’t waste too much time putting them in the tank,” he said. “We try not to put too much strain on them.”

The groundfish are then brought to Bar Harbor’s town pier, where they are transferred to live tanks aboard a pickup truck, and driven to Salsbury Cove.

Carter catches dogfish — the 3-foot-long sharks that are the laboratory’s staple — in his dragnet as well. Although they are fighting and flapping when the net comes in, he worries about the stress that dragging puts the dogfish under. Rather than take these dogfish for the lab, he throws them back.

Instead, Carter sets out a gillnet to catch dogfish, leaving it out only a couple of hours, and hauling it in by hand to make sure that the sharks suffer a minimum amount of pressure from the net. He then transports them by boat to the laboratory’s Salsbury Cove dock, where they are transferred directly to live tanks.

“The ability and willingness and intertest in getting these fish back to us in good health makes Jon very valuable to us,” McCrimmon said. “Jon really knows the waters of Frenchman Bay and the fish that are there.”

In return, the laboratory gives Carter a regular income that buffers him from roller-coaster prices and the vagaries of shellfish population. Carter says that his real love is still lobstering, but his contract with the laboratory provides him security and variety.

And, though Carter would never admit it, he thinks a bit like a scientist. His informal observations of the Frenchman Bay environment has made him a point man in the laboratory’s recent efforts to understand the bay and preserve it.

“He’s the guy that’s out there. He knows how the system is working,” McCrimmon said. “Just like we couldn’t do our work without a Frenchman Bay, we couldn’t do our work without a Jon Carter.”