PORTLAND, Maine (AP) — This year’s marine heat waves and spiking ocean temperatures foretell big changes in the future for some of the largest fish in the sea, such as sharks, tunas and swordfish.

The rising temperatures of the oceans are especially dangerous for these fish because warming makes their open-water habitats less suitable, scientists who study the species said. Loss of habitat could largely remove some of the most important predators — and some of the most commercially important seafood species — from the ocean.

One recent study, from Woods Hole Oceanographic Institution in Massachusetts, predicts that some large species could lose 70 per cent of their habitat by 2100. It’s a sign that this year’s high temperatures aren’t an anomaly but a warning about what the ocean’s future could hold with climate change.

Species of large fish such as marlin and skipjack live in areas that are among the fastest warming ocean regions, projected to increase by up to 10 degrees Fahrenheit (six degrees Celsius) by the end of the century, said Camrin Braun, a marine scientist and an author of the Woods Hole study. That much warming would prompt widespread redistribution of the animals, potentially fundamentally changing sea ecosystems, Braun said.

“Across the board, with life histories so different, we see this consistent signal of loss of habitat,” Braun said. “For sure, their habitat will change. How they respond to that is an open question.”

The heating of the world’s oceans is a longstanding focus of climate scientists, and warming has accelerated this year. Earlier this year, the global average ocean sea surface temperature jumped two-tenths of a degree Celsius (0.36 degree Fahrenheit) in a period of a few weeks, surprising even scientists who have grown accustomed to surging temperatures.

Temperatures the world over were hotter than any time in recorded history in July. Some scientists have placed the blame for the warm year at sea on this year’s El Nino climate pattern on top of human-induced climate change.

For large species of fish, the protracted warming can be disruptive because of their own thermal preferences, said Janet Duffy-Anderson, chief scientific officer of the Gulf of Maine Research Institute in Portland, Maine. Large fish are often highly migratory, and increased warming could result in the species moving to northern or deeper waters in search of more ideal temperatures, she said.

The Gulf of Maine, located off New England and Canada, is warming especially quickly.