Rio Grande Cutthroat Trout’s Varied Life History Strategies May Help Species Respond to Climate Change

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In a new study supported by the NCASC, researchers look for variation in life history patterns across stream conditions in the remaining range of a threatened endemic fish.

Yellow, red, and green fish with spotted tail and white underbelly lays across man’s wet, gently cupped hands.

Rio Grande cutthroat trout collected by Willow Creek, New Mexico. Photo by Chris Kitcheyan, USFWS.

(Public domain.)

As temperatures around the world continue to rise, cold-loving species are being increasingly driven into new or shrinking ranges in search of cooler climates. High elevation regions, such as those on mountaintops, can serve as “climate refugia” for species unable to cope with lowland heat. For example, the Rio Grande cutthroat trout, the highly-threatened state fish of New Mexico and the southern-most subspecies of cutthroat trout, is now confined to only a few Rocky Mountain streams in Colorado and New Mexico after experiencing an 88% decrease in range size over the last 150 years. Yet even if species find mountain refuges, their new environments can alter their growth, development, and survival in ways that could have important evolutionary consequences.

In a recent paper published in Ecology of Freshwater Fish, NCASC fish biologist Abigail Lynch and other USGS and State coauthors explored how stream conditions in climate refugia waterways affect the growth and maturation of Rio Grande cutthroat trout. The researchers surveyed fish across eight sites in New Mexico in streams representative of the range of temperatures, flow rates, and trout densities across the species’ current range. The researchers then combined the data from their mark-recapture study with a previous study on trout age structure to build demographic models estimating the maturation of Rio Grande cutthroat trout in warm and cold streams.

They found that trout in cooler streams matured more slowly and grew larger than trout in warmer streams (although the confidence intervals of the growth models overlapped). Furthermore, trout with these slower life histories were more likely to survive longer and grow larger in cooler streams, while the opposite was true in warmer streams. This indicates that Rio Grande cutthroat trout can exhibit adaptable traits in their life history strategies, potentially conferring differential reproductive benefits across the new environmental conditions the species will experience in the face of climate change. These findings can be used to inform the conservation and management of Rio Grande cutthroat trout populations vulnerable to the effects of climate change and invasive species.

This study was part of the larger NCASC funded project "The Effects of Drought on Rio Grande Cutthroat Trout: The Role of Stream Flow and Temperature."

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