Spring is arriving earlier than it used to in the Gulf of Maine, increasing average water temperatures and affecting the migratory patterns of fish species that are key to Maine’s marine ecosystem and coastal economy, according to a new federal report.

Over the past eight years, the date that scientists use to mark the transition to spring based on water temperature has gotten earlier by roughly two weeks for oceans off the northeastern and mid-Atlantic states. Likewise, the date for the transition to fall is falling later in the year, according to the report by the National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center.

A similar trend is playing out in the Gulf of Maine.

“The spring transition date, currently identified as mid-May, is likely to shift to early April, and the fall transition, currently identified as mid-November, will likely shift well into December,” NOAA oceanographer Kevin Friedland said in a statement about the “Ecosystem Advisory” report. “This implies that the summer portion of the year, based on the transition temperatures, will increase by nearly two months to about 240 days. The extended summer period will have a significant impact on the living marine resources on the shelf. Organisms living in the Northeast Shelf ecosystem will have to deal with the challenges of a longer summer and competition from warm tolerant species entering their habitats.”

Released every six months, the NOAA report attempts to show how changes in water temperatures are affecting fisheries from North Carolina to Maine.

The spring thermal transition date for the Gulf of Maine fell around May 20 this year, according to NOAA. While dates fluctuate year to year, the date in the Gulf of Maine had been holding relatively steady at around June 1 from 1982 to 2006. As a result of the change, marine organisms from northern shrimp to lobster are changing behavior even as species typically found to the south, such as black sea bass and squid, are moving into Maine waters.

“The idea that spring is starting earlier and fall is ending later is really important and certainly something we have seen here in Maine,” said Andrew Pershing, chief scientific officer at the Gulf of Maine Research Institute, who was not directly involved in the NOAA study. “And it has a direct impact on the lobster fishery and the other fisheries we have here.”

In fact, the NOAA report predicts that both the spring and fall transition points could continue to change by another three to four weeks by 2100, which would mean nearly two additional months of warmer weather for coastal areas from North Carolina to the Canadian Maritimes.

Those findings, combined with other research on water temperatures and shifting fish migration, illustrate how conditions are changing in northeastern oceans.

Gulf of Maine water temperatures during the first six months of 2014 were lower than the record-setting levels of 2012 but were still above the long-term mean. Oceans off the coasts of southern New England and mid-Atlantic states saw larger temperature drops from 2012, illustrating the complexities of even regional climate systems.

The Gulf of Maine Research Institute, in research released earlier than the NOAA report, found that water temperatures in the gulf are rising faster than those in 99 percent of the world’s oceans.

Climate change may be a hotly debated topic among politicians but New England fishermen say they are already seeing big changes in the marine environment. Maine’s current lobster boom is attributed in large part to the fact that the lobster population center is creeping steadily northward in search of cooler waters. At the same time, species such as Atlantic cod and northern shrimp that were once mainstays of the Maine coastal economy are so depleted off Maine that federal regulators have shut down the fisheries.

Maine fishermen are also dealing with spiny dogfish, green crabs and other species that have moved in and are now disrupting or displacing more commercially viable species. Meanwhile, there are growing concerns that rising acidity levels in the oceans due to elevated carbon dioxide levels in the air could affect the shell-making abilities of lobsters, clams and other shellfish.

Earlier this month, federal regulators canceled the Gulf of Maine shrimp season for a second year in a row. While research continues, scientists believe the warming gulf is likely a key culprit in the collapse of the shrimp population.

The Gulf of Maine shrimp population took a major hit in 2012 when average ocean temperatures along the northeast coast hit a 150-year high. As a result, the number of spawning-age shrimp in the gulf today remains extremely low even if the survival rate of shrimp born last year was “fairly good,” according to Maggie Hunter, a marine resource scientist at the Maine Department of Marine Resources who monitors the species.

Those were key factors in the Atlantic States Marine Fisheries Commission’s decision to cancel the upcoming winter shrimp season in order to allow the population to continue to rebound. The season was canceled last year, too.

“Things are going to get worse for at least a year before they get better,” Hunter said.

The NOAA report also contains some potentially alarming results about phytoplankton, a tiny marine organism that is a critical component to the oceanic ecosystem. The spring bloom of phytoplankton in the Gulf of Maine was so small in 2014 that it barely registered as a bloom based on the way NOAA tracks the beginning and end of the growth spurts. That could have implications on species – including shrimp – that depend on phytoplankton.

NOAA’s Friedland said many commercial species reproduce in winter and fall so that young emerge in time to benefit from the spring bloom.

Pershing said the NOAA report shows that even when conditions close to shore look normal, as they did this year for much of Maine, the story about the whole gulf is much more complex.

“I think it underscores how quickly this ecosystem has changed and how these changes are persistent,” Pershing said.