Fish in southwest facing dire straits.

• Position: Ecosystems - Brief article

Fish species native to a major Arizona watershed may lose access to segments of their habitat by 2050 as surface water flow is reduced by the effects of climate warming, suggests research published in the Proceedings of the National Academy of Sciences. Most of these fish species, found in the Verde River Basin, already are threatened or endangered. Their survival relies on easy access to various resources throughout the river and its tributary streams. The species include the speckled dace, roundtail chub, and Sonora sucker.

A key component of these streams is hydrologic connectivity--a steady flow of surface water throughout the system that enables fish to make use of the entire watershed as needed for eating, spawning, and raising offspring. Models that researchers produced to gauge the effects of climate change on the watershed suggest that, by the mid 21st century, the network will experience a 17% increase in the frequency of stream drying events and a 27% increase in the frequency of zero-flow days.

"We have portions of the channel that are...