Pink salmon could be another animal threatened by global warming and climate change around the world, according to a new study. Acidification of freshwater systems, mostly driven by carbon dioxide in the atmosphere, is driving downward pressure on populations of the fish.

University of British Columbia researchers examined pink salmon for 10 weeks, from when they were in eggs until they would migrate to the open ocean. One group of the fish were raised in water much like that found in the wild today, while the other group lived in water containing levels which could be present in freshwater sources a century from today.

Researchers found that fish raised in acidic water were not able to smell their surroundings as well as those in the control group. This ability is necessary for the animals to find food and avoid predators. The journey taken by salmon, well-known for swimming to their ancestral homes to mate, could also be affected by dropping pH levels in water.

Ocean acidification has been studied extensively by environmentalists, although not as much attention has been paid to the role of increasing concentrations of acid in ponds, lakes, and rivers.

"Most of the work on acidification has been in the ocean, yet 40 percent of all fish are freshwater. We need to think about how carbon dioxide is affecting freshwater species. We found that freshwater acidification affects pink salmon and may impact their ability to survive and ultimately return to their freshwater spawning grounds," Colin Brauner from the University of British Columbia said.

The study also found that pink salmon raised in acidic environments are less able than normal to utilize oxygen while undergoing physical exertion. This deficit could hinder their ability to escape predators, researchers noted.

"The increase in carbon dioxide in water is actually quite small from a chemistry perspective so we didn't expect to see so many effects. The growth, physiology and behavior of these developing pink salmon are very much influenced by these small changes," said Michelle Ou, lead author of the study.

Salmon entering the ocean for the first time are still small when they arrive, and could be disproportionately affected by lower-than-normal PH levels in the global ocean.

Future research will examine how increasing levels of acid in water will affect other species of salmon, as well as possible long-term effects of the acidity.

Analysis of how pink salmon could be affected by the increase in acid in freshwater sources around the world was published in the journal Nature Climate Change.