In Hot Water

Warming ocean waters are one of many climate change consequences, and scientists have observed fish migrating to stay within their preferred temperature range. Janet Nye, a UNC-Chapel Hill marine scientist, wants to understand how a warmer environment will affect these animals to help fisheries better prepare for the future.

October 12th, 2021

It wasn’t long after Glenn Skinner learned to walk that he learned to fish. Growing up in Morehead City, like many others in the area Skinner comes from a long line of commercial fishermen.

“I’ve made some form of income every year since I was 3 years old off the water,” he says. “I’d go with my dad and whatever I caught he sold and paid me for it.”

Skinner grew up catching anything that was bringing in money that year — from clam and oyster to flounder and crab. These days, he enjoys recreational fishing and is the executive director of the North Carolina Fisheries Association, acting as an advocate for the commercial fishing industry.

“There’s still a lot of families that are three, four, five-generation commercial fishing families, and the loss of fishing would destroy a lot of the fishing communities up and down the coast here,” he says.

In the face of climate change, these coastal communities have a multitude of challenges ahead of them. One threat is ocean warming — the focus of UNC marine scientist Janet Nye.

More than 90 percent of the global warming in the past 50 years has occurred in the ocean, which acts as Earth’s coolant, absorbing most of the heat that is trapped in the atmosphere due to the build-up of greenhouse gases. While this slows rising temperatures of the planet more broadly, the oceans are reaching a breaking point, as evidenced by issues like sea level rise, ocean heat waves, coral bleaching, and the melting of glaciers and ice sheets.

This increase also affects the animals living in these ecosystems. Fish are cold-blooded, meaning their body temperature is determined by the water around them. Temperature changes can have numerous impacts on them, from growth and reproduction to the timing of migration. Marine scientists have observed some species move further north or south — towards their respective pole — to stay within cooler waters.

Nye studies the temperature tolerances of fish to determine the highest and lowest temperatures different species can withstand. Ultimately, these limits determine where a fish can thrive or, at least, survive.

“If we can understand how climate change is going to affect our coastlines and the people on the coast, we can better prepare for the future,” she says.

Her team conducts experiments by increasing or decreasing water temperature in a small fish tank by about 32 degrees Fahrenheit in one hour. When the fish loses its equilibrium it starts to tip over, and they know a limit has been reached.

While oceans are not going to undergo dramatic temperature changes in such a short amount of time, this rapid assessment helps Nye’s team understand how temperature affects the abundance of certain fish species. They can plug their data into population, ecosystem, and global-climate models to determine how it affects reproductive success, growth, and distribution, among other factors, which can help fisheries managers determine harvest limits.

“The coast contributes greatly to North Carolina’s economy so we really want to be able to anticipate how that’s gonna affect the fish and help fishermen respond to that so they can plan for the future,” Nye says.

Nye says working with fisheries is essential to find solutions to climate change and other environmental problems. She is working to build relationships with local fisheries and also using census data to identify coastal communities that are most vulnerable to climate change and need the most help adapting to changing ocean conditions. Skinner says he can get on board with this type of teamwork.

“I think the only way we’ll figure this out is to get fishermen and researchers to work together,” Skinner says. “Fishermen are like canaries in the coal mine — we’re the first ones to notice when a species starts to decline. We see fish kills and water quality issues on a regular basis. We see the seagrass disappearing. This is stuff we need to collaborate on to ensure the science is solid because our livelihoods rely on it.”

Janet Nye is an associate professor in the Department of Earth, Marine, and Environmental Sciences within the UNC College of Arts & Sciences.

Glenn Skinner is the executive director of the North Carolina Fisheries Association.