Climate is Changing – and so are Salmon

River temperatures in the Pacific Northwest are rising and salmon aren’t doing so hot.

Many scientists and fisheries managers are concerned that unless something is done, it is not clear that salmon and the surrounding billion-dollar industry will be able to keep up with climate change.

This February, a coalition of environmental organizations sued the Trump Administration for failing to mitigate these warming waters. They assert that under Scott Pruitt, the Environmental Protection Agency (EPA) has neglected its duty under the Clean Water Act to address “temperature pollution” in the Columbia and Snake Rivers in the Pacific Northwest.

Snake River Waterkeeper is one of the organizations involved in the suit. Instead of hoping rivers don’t get hot enough each year to kill hundreds of thousands of fish like in 2015, says Snake River Waterkeeper Executive Director Buck Ryan, “we’re demanding that agencies make a plan to lower temperatures so endangered populations can spawn and recover.”

In the summer of 2015, the majority of the 500,000 migrating sockeye salmon in the Columbia River died while returning to their spawning grounds, an event many federal and state fisheries biologists attribute to unusually warm waters. Mary Peters, a microbiologist who works for the U.S. Fish and Wildlife Service, told The Seattle Times, “The water temperatures in the Lower Columbia are physiologically unsustainable for salmon […] It’s crazy.”

Though the current administration is not prioritizing climate change mitigation, the science is clear that climate is warming and warmer temperatures are not ideal for most cold-water fish. As climate change continues to alter salmon habitat, how might these populations respond?

How are salmon plastic?

Species generally adapt to environmental change in three ways: through the slow process of evolution; by moving to a new location with a more suitable climate; or by becoming ‘plastic.’ Plastic adaptations don’t involve actually turning into plastic, but rather, they allow organisms to adapt to conditions several ways, including the ability to turn specific genes on or off based on different environmental conditions.

Warmer waters have already driven plastic shifts in salmon populations in the Pacific Northwest. For example, according to a study conducted by scientists from the National Oceanic and Atmospheric Administration (NOAA), an endangered population of Snake River Chinook salmon has changed the timing of its migration in response to a warming climate. Salmon in this population migrate downstream earlier in years when they experience warmer temperatures in fall and spring.

That may not seem catastrophic, but in addition to shifting salmon migration behavior, warmer waters can make different salmon populations more susceptible to disease, speed up or slow down their growth and development, and pose challenges to egg development.

High temperatures can also affect salmon heart function. When temperatures rise, activities like swimming or searching for food require more energy, and with higher energy demands come higher oxygen demands. If the heart cannot beat fast enough to supply the oxygen required, the salmon is in trouble.

Western University senior researcher Dr. Bryan D. Neff collaborated with a team of Canadian scientists to investigate this link between temperature and heart rate. They wanted to know whether salmon could increase their maximum heart rates to adapt to higher temperatures.  This response would be an example of a plastic adaptation.

Dr. Neff and his team raised salmon under two different temperature scenarios: current and 4 degrees Celsius warmer. Neff chose 4 degrees because that’s the amount the Intergovernmental Panel on Climate Change says we’re in for by 2100 if we fail to curb our current rate of emissions

Scientists then subjected both groups to warmer temperatures, and the salmon showed a plastic response. Compared to salmon raised in cooler waters, salmon raised in warmer conditions were better off; their hearts exhibited a higher maximum heart rate and were more capable of keeping up with the higher oxygen demands in warmer waters.

Plastic adaptation in a changing climate

Dr. Neff and his collaborators also designed their study to investigate whether these heat tolerant genes could be passed down. Their results reveal that the fish’s genes greatly influence their hearts’ ability to tolerate heat. This study is the first to show that a Pacific salmon has both the physiological and the genetic possibility of adapting to rising temperatures.

The question remains, however, as to whether salmon adaptation can keep pace with a rapidly changing climate. If not, they will not survive into the future.

Without salmon in the Pacific Northwest, humans would lose a billion-dollar fishing industry, hundreds of thousands of jobs, and a species of significant cultural value.

Ecosystems that support salmon would also suffer. For example, the endangered Southern Resident orca population depends on salmon for sustenance, and forests surrounding salmon streams depend on spawning salmon nutrients to fertilize their growth.

Ultimately, warmer waters threaten these cold-water fish, and climate change may continue to inflict devastating impacts on these populations now and into the future. The survival of salmon should not hinge how quickly they can adapt to human-induced environmental change.

Featured image courtesy of NPS/ S. Huffman