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SDSU teamed up with the Woods Hole Oceanographic Institution, NOAA and other institutions to model the impact of warming oceans on large migratory fish.

By Susanne Clara Bard

New research published in Science Advances shows climate change is causing widespread habitat loss for some of the ocean’s top fish predators, driving these species northward. The shift is expected to significantly impact the food web, fisheries and coastal communities.

“Climate change is expected to cause the status quo for where these species are and how they live to fundamentally change,” said lead author Camrin Braun, an assistant scientist and marine ecologist at the Woods Hole Oceanographic Institution (WHOI).

The research was led by WHOI, with collaboration from San Diego State University, the National Oceanic and Atmospheric Administration (NOAA), and several other U.S. institutions.

The researchers studied 12 large fish species — including several types of sharks, tuna and billfish — inhabiting the waters of the Northwest Atlantic coast from Haiti to the Maritime provinces of Canada, as well as the Gulf of Mexico, areas undergoing rapid changes in sea surface temperatures.

These species spend a lot of time traveling — sometimes across entire ocean basins,” said SDSU biologist and conservation ecologist Rebecca Lewison. “They play important ecological roles in regulating other species, in changing the abundance of other species.”

Species Changes

The study modeled two types of shifts in the fishes’ habitat due to climate change: shifts that have already occurred and predicted future habitat shifts based on climate models. Satellite data from NASA plays an important role in tracking these shifts .

Sea surface temperatures are expected to rise by 1-10 degrees F by 2100, according to the Intergovernmental Panel on Climate Change.

“Certain species are very sensitive to changes in ocean temperature,” said Lewison. “What that often means is that a part of the ocean that was one temperature has now shifted consistently to another, and that’s how fish lose habitat.”

The study revealed that suitable habitat for most of the species studied — including yellowfin tuna, shortfin mako sharks and white marlin, among others — is expected to decrease in the coming years. Some species could lose up to 70% of their habitat. But the habitat of a few species, like blue marlin, is actually expected to expand somewhat over time.

Some species may be more adaptable than others, according to Lewison. However, the habitats of all of the species in the study show a significant northward shift in habitat, to cooler waters.

“Ocean temperatures off of Florida hit all-time highs recently,” said Lewison. “These highly migratory species do not want to be in that water.”

The northward shift could spell problems for the fisheries that depend on these species for their livelihoods.

“Fishermen are noticing that there are shifts, that there are changes,” said Lewison. “They’re noticing in certain places they have to travel farther to the fishing grounds, and that a lot of these warming episodes are really having a big impact.” The changes could mean some vessels out of certain ports may lose access to certain species, causing fisheries and fishing communities to suffer, she added.

Lewison said the research team was careful to ensure that the work resonated with the fishing community and the data they collected were representative and accurate.

Dynamic Management

Historically, strategies for managing fish have been static. But it’s important to treat marine systems as dynamic and changing, and in some places that change is happening faster than expected, said Lewison. The good news is that this study and others like it are providing the scientific data needed for marine conservation and fisheries management efforts.

“Dynamic ocean management is a new approach that a lot of management agencies — both in the US and overseas — have been embracing,” she said. “When we think about climate change, it’s easy to think about changes that are coming in the future. One of the important things about our research is that it demonstrates that climate change is here now. We are already dealing with it both on land and in the oceans. And there is so much data and science we can use to support climate readiness and climate resilience.”

The research was supported by a NASA Ecological Conservation program grant, the NOAA Integrated Ecosystem Assessment Program, the Postdoctoral Scholar Program at WHOI, and the Dr. George D. Grice Postdoctoral Scholarship Fund at WHOI.

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