In previous research, Perkin and Gido found that river fragments less than 100 kilometers make it difficult -- if not impossible -- for certain fish species to survive.
"Some fish species will release their eggs into the river and these eggs have to drift downstream for a certain distance to develop," Gido said. "They basically cannot persist in fragments less than 100 kilometers."
Additionally, reservoirs and ponds behind dams often are stocked with nonnative fish, such as largemouth bass, that can move into the stream fragments and prey on native fish. This increases the effects of shrunken rivers.
"As the water levels decline, if you have a nonnative predator in the system, then the predators' effects are much stronger and have a more drastic effect on fish," Gido said. "We have seen a gradual decline in native diversity over time. The drought exacerbates any of the effects because with fragmentation, if the stream is dry and the water is lower, the fish are unable to move around a barrier."
Gido said countermeasures, such as removing nonnative fish predators, may prevent more native fish from disappearing. Nonnative predator removals are currently under way in the San Juan and Gila rivers, Gido said.
"It might not be something that you can do all the time, but during drought conditions it might be possible to remove predators to give native fish a chance and maintain diversity," Gido said.
Maintaining diversity is important to maintain healthy river ecosystem functions, Gido said. As part of the ecosystem, fish can influence the cycling of stream and river nutrients. Streams filter nutrients that flow to rivers or other large bodies. When this balance is off, too many nutrients can result in negative effects, such as harmful algae blooms.
A lot of native species of fish also provide recreational opportunities,
|Contact: Keith Gido|
Kansas State University