Study shows significant loss of fish habitat by mid-century
FRISCO — Big sections of vulnerable stream habitat for native fish in the Southwest are likely to disappear by mid-century as global warming causes stream flows to dwindle.
By 2050, stream-drying events could increase by 17 percent, and the number of zero-flow days could go up by 27 percent in the Verde River Basin, affecting species like speckled dace (Rhinichthys osculus), roundtail chub (Gila robusta) and Sonora sucker (Catostomus insignis).
The drying trend will fragment aquatic habitat, hampering feeding and spawning. Some populations that are already isolated may very well disappear, said Ohio State University researcher Kristin Jaeger, an assistant professor at the School of Environment and Natural Resources.
“We have portions of the channel that are going to dry more frequently and for longer periods of time,” Jaeger said. “As a result, the network will become fragmented, contracting into isolated, separated pools.
“If water is flowing throughout the network, fish are able to access all parts of it and make use of whatever resources are there,” she said. “But when systems dry down, temporary fragmented systems develop that force fish into smaller, sometimes isolated channel reaches or pools until dry channels wet up again.”
This study covers climate change’s effects on surface water availability from precipitation and temperature changes. It does not take into account any withdrawals of groundwater that will be needed during droughts to support the estimated 50 percent or more increase in Arizona’s population by 2050.
“These estimates are conservative,” said Jaeger, who conducted the study with co-authors Julian Olden and Noel Pelland of the University of Washington. The study is published in the Proceedings of the National Academy of Sciences.
The modeling suggests the biggest impacts to streamflows can be expected during the critical spring spawning season, when fish travel longer distances to access necessary habitat.
Flowing portions of the system will diminish between 8 and 20 percent in spring and early summer, producing lengthier channels that will dry more frequently and over longer periods of time. These changes will reduce available habitat for fish and force them to travel longer distances for resources once channels rewet, Jaeger said.
The fish are already subject to stressors on the system, including both surface and groundwater extraction for irrigation and drinking water, loss of habitat and the introduction of nonnative species that prey on the native fish, Jaeger said. The overall system’s connectivity is also already compromised, as well, because of existing dry conditions in the American Southwest.
“These fish are important cogs in the wheel of this greater ecosystem,” Jaeger said. “Loss of endemic species is a big deal in and of itself, and native species evaluated in this study are particularly evolved to this watershed.
“In this river network that currently supports a relatively high level of biodiversity, the suite of endemic fish species are filling different niches in the ecosystem, which allows the system to be more resilient to disturbances such as drought,” she concluded.