In 2013 researchers Chris Sergeant was doing some routine monitoring of water quality on the Sitka’s Indian River when he noticed something unusual on the oxygen monitor.
The span style=”font-weight 400 ;”>”It was close to zero. It was extremely, very low,” Sergeant added. “And there were fish dying. Coho juveniles and cutthroat trout. Also, a large portion of adult salmon were strays from the hatchery.”
The stream was clogged, full of fish that were unable to get enough oxygen. Such deaths of salmon have been documented for more than 100 years, yet their causes aren’t understood well. A new research conducted by Sergeant as well as his team of researchers suggests an increasing number of salmon raised in hatcheries within Southeast Alaska could put pressure on miles of salmon streams, which are already at risk because of climate changes.
“We have a lot of salmon breathing in too high levels of oxygen,” Sergeant said. “It’s unnaturally high in number of salmon.” .”
The water that flows through streams and rivers contains oxygen dissolved in it that fish and salmon breath through their gills. If the fish don’t receive adequate oxygen supply, they may drown. In less severe cases the lack of oxygen may hinder salmon’s difficult journey upstream.
The span style=”font-weight 400 ;”>”They could not reach the spawning grounds on sufficient time, or even have the necessary time for them to reproduce,” Sergeant said. “So there’s lots of subtle effects that can occur as well as massive death-offs .”
Scientists have warned for a long time that hatchery salmon be in competition with wild salmon for resources such as oxygen. For more than 50 years the hatchery industry across Alaska has increased, particularly for chum and pink salmon.
These populations are expected to return to their hatchery once they spawn. However, they tend to wander into streams that are wild. The study’s researchers say it can put salmon that are wildthat includes species with higher value such as coho, chinook and sockeye at greater chance of being smothered.
The study includes over 10,000 miles of habitat for wild salmon within Southeast Alaska that are close to hatchery release sites, thereby creating the possibility of overcrowded streams.
As for hypoxia, the risk for salmon is exacerbated because of climate change that is caused by humans. Temperatures rising across this region are linked to the death of salmon in recent years. Furthermore, the warmer water is less able to hold oxygen.
If hot temperatures are accompanied by drought conditions, salmon streams are predisposed to hypoxia. The reason is that a good salmon habitat is arid and swiftly flowing. This kind of water is oxygen-rich.
The span style=”font-weight 400 ;”>”The more the water twirls and foams like a rapid, the greater chance that it will exchange energy with the air,” Sergeant said. “That tumble motion of water is in essence injecting oxygen .”
Climate change is likely to bring more rain to Southeast Alaska overall, but the region is facing an increasing risk of drought. Extreme rainfall is likely to be accompanied by more dry times particularly in the summer. The decline in snowpack in the mountains can create drought.
Based on Ryan Bellmore, a US Forest Service researcher who co-authored the study snowpack can be described as an account on the bank of the watershed.
“span” style=”font-weight 400 ;”>”And we’re more likely to be in an economic red zone,” Bellmore said.
Water is preserved in the mountains of the north during the winter, and slowly melts through the spring and summer months to feed the streams and rivers. Without it, streams that are fed by salmon might dry up and slow down during the summer temperatures, which can lead to a drop in oxygen levels.
And as climate change places stress on Southeast Alaskan watersheds, cramped conditions could continue to choke wild salmon.
