PORTLAND – Even slight changes in temperature, salinity and weather patterns due to global warming could have a dramatic impact on marine life in the Gulf of Maine and, therefore, the state’s commercial fishing fleet, biologists and economists warned Thursday.

The daunting challenge, the speakers said, will be predicting and responding to those effects as the world enters the uncharted waters of climate change.

“We all want to get to that prediction. It’s what everybody demands, but that’s difficult to do, … and in the policy world, you can’t wait until all of this is clear,” said Lewis Incze, a senior research scientist at the University of Southern Maine.

Incze was part of a conference on climate change in the northwest Atlantic Ocean held at the Gulf of Maine Research Institute.

The purpose of the conference – organized by the University of Maine School of Law’s Center for Law and Innovation and GMRI – was to spark a dialogue among biologists, state and federal regulators, educators, economists and others on policy issues related to global warming.

Fisheries experts who spoke Thursday morning stressed that there are still many uncertainties about how rising global temperatures will affect species in the Gulf of Maine. But they said evidence is mounting that changes are coming, or are already here.

Andrew Pershing of UM’s School of Marine Sciences detailed how he and a colleague found evidence that low-salinity meltwater entering the far Northern Atlantic in the early 1990s had major effects throughout the oceanic food chain.

The “freshening” caused a massive bloom in a type of tiny crustacean that, in turn, fed a population boom in herring. But endangered right whales that feed on the rice-sized crustaceans experienced sharply lower reproduction success.

More freshwater is expected to enter the Atlantic as worldwide temperatures rise, with the biggest increases expected near the poles.

That can change water circulation as well as stratification of water layers, affecting the tiny sea creatures that are at the bottom of the food chain, Pershing said.

“This is, I think, one of these major changes in the North Atlantic that people looking at [and] ecosystems are going to have to wrestle with,” Pershing said.

As ocean and weather conditions change, the Gulf of Maine can expect some species to struggle and other new species to move in, said Kevin Friedland, director of the Cooperative Marine Education and Research Program run by the University of Massachusetts and the National Oceanic and Atmospheric Administration.

That may mean cod will continue to decline while species such as hake or even Spanish mackerel may establish themselves in the gulf, he said.

All of this will have dramatic implications for Maine and New England’s fishing industry, speakers predicted.

Dan Holland, a research scientist who studies economic issues with GMRI, said the region’s stringent fishing regulations have resulted in more specialized fishermen.

But as a consequence, this lack of diversification may leave them more vulnerable to rapid changes in the fisheries. The changes will also necessitate more management cooperation between the U.S. and Canada, he said.

“We should be thinking about new fisheries that are emerging, whether because of climate change or other factors,” Holland said.

Those changes may also force states and the federal government to make tough choices on what species are worth fighting the hardest to save from total collapse and which must be left to nature, said Robert Johnston, an economics professor at the University of Connecticut and director of that state’s Sea Grant College Program.

“In a changing climate, you may not be able to protect all of the resources that you want to, so how do you decide where to spend that money?” Johnston said.

A live blog of the conference can be found at http://lawandinnovation.blogspot.com.