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Climate change threatens California freshwater fish. We can do something about it, experts say.

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Nutria, a giant South American rodent, is an invasive species in California’s San Joaquin River Delta. The California Department of Fish and Wildlife has a plan to exterminate animals, but it will take more money and staff.

Fish die-offs in freshwater lakes are an increasing threat in California, and experts say climate change is to blame.

Researchers from UC Davis and Reed College in Portland, Ore., found a strong link between fish deaths in freshwater lakes in Wisconsin and hot summers. They predict that fish die-offs will double by 2050 and quadruple by 2100 in Wisconsin.

Andrew Rypel, a UC Davis wildlife, fish and conservation biology researcher, said we should expect similar effects in California.

He told The Bee in an interview that California lakes may be even more vulnerable to the effects of climate change than those in Wisconsin, because they host many sensitive cold-water species.

“Freshwater species are uniquely challenged by climate change,” Rypel said. “Marine fish or migratory waterfowls, like ducks, can just move north as climate change occurs, but fish in lakes... they can’t really do that: migrating isn’t an option.”

But Rypel said there are ways to protect Californian fisheries - a $5.2 billion industry that employs nearly 40,000 people every year, according to the American Sportfishing Association. We can’t control water temperatures, Rypel said, but we can make fish populations stronger.

“This is actually a big focus in California, they call it resilience: adding resilience to the fish population,” he said.

Why and where are fish dying?

“We know very little about how climate change is going to affect lakes and lake fisheries,” Rypel said. “This study is one of the first that tries to connect the dots.”

Turns out, Rypel said, that fish kill-offs are pretty easy to predict: the higher the summer temperatures, the more the fish deaths.

“Fish breathe oxygen just like we do and oftentimes bad conditions temperature-wise can also be bad oxygen-wise,” he explained, “so if you’re a cool-adapted species of any variety, warm temperatures are generally not good for you and you could be subject to kill.”

The California Department of Fish and Wildlife has also been looking into the effects of climate change on freshwater fish populations. In a 2014-2017 report, the department studied fresh waters in counties across the state. In the Central Valley, they focused on three counties: Butte, Sacramento and Yuba.

They found that high summer temperatures were not only worsening the quality of the water, but drying out freshwater bodies that hosted endangered species. “The effects of the drought often resulted in higher water temperatures,” officials wrote in the study. “Aquatic species were frequently stranded as streams dried.”

Even when the 2011 drought ended in March 2017, temperatures still rose above 59-64 degrees Farenheit (15-18 degrees Celsius), endangering salmon and steelhead. That’s the same year that officials in Lake County, north of Sacramento, found “dead fish islands about the size of three football fields,” KTVU reported.

Officials detected hundreds of fish kill-offs during the study in all three counties and five freshwater bodies they analyzed: Butte Creek, Big Chico Creek and Feather River in Butte County; American River in Sacramento County; and Yuba River in Yuba County. And they predicted the problem could worsen.

“Future climate change predictions suggest that these threats may increase in frequency and severity in the coming years, potentially adversely affecting fish and other aquatic resources,” according to the report.

What can we do about it?

Rypel says that to prevent fish die-offs, we’ve got to make fish more resilient. “How do you do that? Well, you can’t really control the temperature,” he said, “so what you have to work on factors you can control.”

The UC Davis study found that the two main factors to pay attention to are harvest rates and land use. An easy fix, Rypel said, is to add vegetation around lakes to protect them from contamination. “Phosphorus pollutants like fertilizers that enter the lake can exacerbate the frequency of fish kills,” he said, “so finding ways to mitigate or lessen the amount of phosphorus that enters the lake could be very important.”

Local communities could also “soak up some of that pollution” by creating more public lands that have high proportions of wetlands.

“If you know that certain lakes are going to be especially vulnerable to climate change, those are places where you want to incentivize ... people to work towards better land use: that’s the key, and that’s the way we should be thinking about this,” Rypel said.

And if people don’t care about the effects fish die-offs will have on the environment, he encourages them to consider the more tangible advantages of protecting California fisheries.

“There’s an argument for doing what’s right,” he said, “but there’s also an economic argument to it: (this) is going to affect the economy and we need to come up with ways to mitigate the effect.”

Meanwhile, efforts to monitor water temperatures, water flows and fish populations continue, the California Department of Fish and Wildlife told the Bee in a statement. “Having identified areas where additional resources are needed allows our agency to prioritize watersheds and species specific data collection that is needed to manage that population,” Senior Scientist Tracy McReynolds said.

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Caroline Ghisolfi, from Stanford University, is a local news reporter for The Sacramento Bee, focusing on breaking news and health care. She grew up in Milan, Italy.
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