LEWISTON – Scientists are cataloging the natural riches of the Gulf of Maine as the debate over offshore drilling intensifies.

President Bush has lifted an executive ban over offshore drilling. The issue has become prominent in the presidential campaign, and was on the Senate agenda before Democrats closed debate on the topic.

Don Perkins, president of the Gulf of Maine Research Institute, which has 30 projects in the works, said he has questions about the impact of oil drilling on critical fisheries habitat and the potential for seepage.

The international Census of Marine Life counts 3,317 species living in the Gulf of Maine. Chief scientist Lew Incze suspects there are hundreds if not thousands left to discover. Incze’s census doesn’t take a stand on drilling.

“It’s really quite dangerous to mix science and advocacy,” Incze said. “It’s still always a bit of a hit or miss as far as what types of reserves you hit.”

The Gulf of Maine Ocean Observing System says the offshore expanse is as deep as 1,500 feet in spots and home to 52 species of commercially harvested fish and shellfish. Lobster is by far the biggest crop with a catch valued at $270 million last year, more than half of the estimated half-billion-dollar fishing economy in Maine.

Despite decade-long predictions of an impending crash, “the resource is really, really healthy,” said Dane Somers, executive director of the Maine Lobster Promotion Council. Perkins said the gulf’s herring resource is robust and mackerel is very abundant.

Sea life in the gulf ranges in size from the endangered 100-plus-ton right whale to the tiny copepods that the right whale eats by the billions each day.

But Incze, who started the marine census in the gulf in 2003 as a pilot site for the international count, said there are still questions about why some stocks aren’t rebounding.

“All in all, the Gulf of Maine is doing pretty well. … At this point in our history, we are doing things in virtually every spot in the ocean in the Gulf of Maine. Someone is fishing, someone is traveling, someone is trying to lay a cable or a pipeline or is transporting oil or is discharging ballast from a ship or wants to mine gravel or wants to grow salmon or mussels,” Incze said.

“The question is, what’s the right amount, and where, and how.”

Members of Maine’s congressional delegation oppose drilling off the gulf.