During a year of severe drought and record heat in the west, many dead Chinook salmon were found along Bart Creek in Chico, California.
California's Chinook salmon (salmon) is disappearing. Every spring, these fish swim into the creeks of California's Central Valley. There, they reach the cold waters, where they lay their eggs or lay their eggs. Then they die, completing their life cycle. (The life cycle is all the changes that occur in a living organism throughout its lifetime.) ）
Salmon have been doing this for hundreds of years. However, that is now changing. The creek became too warm. Some places are 10 degrees above average. This is due to the high temperatures in the area. And, due to the drought, the water level in the creek is too low. (Drought is when an area receives less rain than normal.) It will happen for a long time. ）
Figure 1. During their annual migration, Chinook salmon swim upstream along the Sacramento River from San Francisco's Golden Gate Bridge through the northern part of the Central Valley.
This spring, an estimated 16,000 Chinooks migrated from the Pacific Ocean to the creeks of the Central Valley. (Migration is the movement of a group of animals from one place to another.) Salmon that migrate in the spring are called spring salmon. Of the 16,000 people who traveled, about 14,500 died. It's all thanks to the valley's hot and low-flow waterways.
Now, these conditions are just as serious a threat to winter migration. Salmon that migrate to rivers in the winter are called winter salmon. It is too early to measure the impact of drought on winter migration. However, experts fear that this could be equally catastrophic.
Colin Purdy works for the state Department of Fish and Wildlife. He is the Environmental Program Manager for Fisheries. He said they want to see enough salmon survive this winter.
But much of the western United States is in drought. Many places have documented the hottest July in history. In California, dry brown landscapes have become the norm. The state has experienced huge wildfires, deadly mudslides and new demands for water supplies.
Drought is also punishing California's abundant wildlife, from birds to bears. Wildlife is also threatened by destructive human engineering and dangerous climate change. (Climate is a weather pattern over a long period of time, usually 30 years or more.) ）
"Salmon is basically like a canary in a coal mine, giving you an idea of what's going on in a freshwater system," John McManus said. He runs the Golden State Salmon Association. As salmon disappear, so may many other creatures in the area.
Image 2. Jason Roberts (left), manager of california's Department of Fish and Wildlife, and biologist Matt Johnson look for salmon on the upper Sacramento River
The Sacramento River is wide and fast-flowing. It is the only winter salmon habitat in the world. (Habitat is the natural environment of living things.) ）
Every December, thousands of Chinook salmon leave the frigid Pacific Ocean. Swim about 325 miles (523 kilometers) upstream into cooler waters. For thousands of years, melting snow and ice from the Sierra Nevada have cooled the sea. This year's snowfall is about half the annual average.
Every year, many salmon return to the same waters as their ancestors to spawn. But some can't because of the low water flow. Drought has made the situation worse. In addition, almost every river or stream in the central valley has a dam. On the Sacramento River, the Shasta Dam insulates salmon from cooler lakes and rivers further north.
To solve this problem, the government built fish ladders and elevators to help the fish cross the dam. But the Chinook population continues to decline.
A long-term plan to help them is currently being discussed. The plan is to reintroduce the Chinook River into parts of the Sacramento River above the dam. But given that salmon populations are already under threat, doing so is both expensive and risky.