Climate change is taking its toll on big fish, the ocean’s main predators

Portland, Maine — This year’s marine heatwaves and rising ocean temperatures portend big changes ahead for some of the sea’s largest fish, such as sharks, tuna and swordfish.

Scientists who study this species said that rising ocean temperatures pose a particular danger to these fish because rising temperatures make their habitats in open waters less suitable. Habitat loss can remove some of our top predators — and some of our most commercially important seafood species — from the ocean.

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

Camryn Brown, a marine scientist and researcher, said that large species of fish such as marlin and skipjack live in areas that are among the fastest warming in the oceans, and temperatures are expected to increase by up to 10 degrees Fahrenheit (6 degrees Celsius) by the end of the century. . Author of the Woods Hole study. This significant warming would lead to a widespread redistribution of animals, which could radically change marine ecosystems, Brown said.

“Across the board, with varying life histories, we see this consistent signal of habitat loss,” Brown said. “Certainly, their environment will change. How to respond to that is an open question.”

The warming of the world’s oceans has long been a focus of climate scientists, and global warming has accelerated this year. Earlier this year, the global average ocean surface temperature jumped by two-tenths of a degree Celsius (0.36 degrees Fahrenheit) in just a few weeks, surprising even scientists accustomed to rising temperatures.

Temperatures around the world were hotter than ever in recorded history in July. Some scientists have blamed the warm year at sea on this year’s El Niño climate pattern as well as climate change caused by human activity.

For larger fish species, prolonged warming could be troublesome because of their thermal preferences, said Janet Duffy Anderson, chief scientific officer at the Gulf of Maine Research Institute in Portland, Maine. Larger fish are often highly migratory, and warming may cause species to move 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.

“I think what we’ll see is a shift in its distribution,” Duffy Anderson said. “We will see a shift in the distribution of marlin and tuna species.”

Large fish are important to the health of the oceans because many of them, such as white sharks, are apex predators and serve as vital parts at the top of the food chain. But some are also economically important to humans as food.

The U.S. swordfish catch was worth about $23 million at docks in 2022 and millions more at supermarkets, restaurants and seafood stands. Albacore tuna have grossed more than $36 million at the docks.

Changes in the distribution of large fish may require major adjustments in the way fishing industries are regulated, said Brown, the associate scientist at Woods Hole. The coming warming “is likely to have significant social and economic impacts on fishing fleets that target” these fish, especially in the southeastern United States, home to lucrative fisheries for species such as bluefin tuna and swordfish, his study said.

Fishing vessels will also need to adapt their strategies by fishing in different places or at different times of the year, said Toby Curtis, a fisheries management specialist at the National Oceanic and Atmospheric Administration who worked on the Woods Hole study. Curtis said the climate models used in the study can help predict and plan for the scale of changes.

The effect of rising water temperatures on fish is complex and the subject of much scientific research. A study published in the scientific journal Nature in August found that marine heatwaves are “not the dominant driver of change” in some species that live near the ocean floor. The study shows that the negative impacts of marine heat waves may be unpredictable, the study authors said.

Thoughtful leadership and management will be necessary to deal with changes in fish distribution without catastrophic results, said Jeb Brogan, campaign director at the conservation group Oceana. He said fish populations depend on healthy habitats, and losing suitable habitat could lead to the species being lost completely.

“If we don’t realize this is coming, it will lead to poor outcomes across the board,” Brogan said. “This is a wake-up call to fisheries managers on both sides of the Atlantic… that we need to change the way these fisheries are managed so that we can adapt, be proactive and conserve fish stocks as they change.”

The potential loss of large fish is one of many consequences of ocean warming that scientists have sounded the alarm about this year. One scientific study said that the collapse of ocean currents that transport heat northward across the North Atlantic could occur by mid-century. In Florida, ocean researchers working for the federal government said coral reefs are losing their colors weeks earlier than usual due to record temperatures.

The threat to big fish is another wake-up call to focus on ocean management in the era of climate change, said Penny Baker, vice president of conservation at Seattle-based environmental group Island Conservation.

“If you’re missing these components in these large fish species, it’s a missing gap in the ecosystem,” Baker said.


Follow Patrick Whittle on X, formerly Twitter: @pxwhittle


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(Tags for translation) Climate and Environment

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