Distinctly Montana Magazine

D I S T I N C T L Y M O N T A N A M A G A Z I N E • S P R I N G 2 0 1 9 84 M O N TA N A i n T R O U T IN GENERAL, HOW WILL TROUT POPULATIONS IN MONTANA FARE IN 2049? Climate projections show that in 30 years, Montana's streams and rivers will get and stay warmer for longer periods of time. Earlier and diminished spring runoff resulting in lower annual average flow levels throughout the year will drive those temperature changes. at's bad news for trout. Trout habitat and range will shrink. e shift from native trout species to non-natives will, in many places, be exacerbated. Due to the stresses of reduced habitat, changing food webs, higher water temperatures, the higher concentrations of water-borne contaminants that are likely to occur with diminished flows (less dilution), and the trend of increasing human movement between waterways means diseases that affect trout are likely to threaten fish health and increase mortality. ese factors are part of what is driving Trout Unlimited's well-established work to improve stream flows, restore habitat, and, generally, keep Montana's waters clean and cold. LET'S TAKE IT SPECIES BY SPECIES—CUTTHROAT, BROWN, RAIN- BOW AND OTHER RELATED FISH. WHAT'S THE OUTLOOK? Montana's native westslope and Yellowstone cutthroat trout will both face similar challenges in the future. As has happened in the past 30 years, so will go the next 30. Both of these species of native cutthroat trout are dependent on cold, clean water, as well as long reaches of connected and complex habitat. As mainstem rivers and major spawning tributaries warm and experience longer periods of lower flows, the range and population of both species of cutthroat face reduction. It's harder to predict what impact on cutthroat reproduction earlier and changing spring runoff will have on these spring- spawning fish. It's likely that their life-cycles will be nar- rowed to fewer and fewer tributaries that maintain the spring spawning habitat and year-round cold temperatures that allow cutthroat to survive. Pure westslope cutthroat range is likely to continue shrinking in western Montana and virtually disap- pear in the upper Missouri. Yellowstone cutthroat, which once were prevalent down their namesake river to the confluence of the Tongue River, will retreat farther into the headwaters of the Yellowstone and isolated stream and lake systems in Yel- lowstone National Park. In addition to shrinking ranges and populations of native cut- throat, these populations are at jeopardy of becoming increasingly hybridized with rainbow trout. Because rainbow trout tolerate higher water temperatures and can spawn in more varied habitat, this wild species of trout will have higher survival, invade more native trout water and, hence, hybridize with native species. e fate of brown trout is also uncertain. While brown trout can tolerate warmer water conditions, they are fall spawners. Because low, summer flows are likely to extend later into the fall, brown trout might lose spawning habitat and be out- competed by spring spawning species. In the last few decades, surveys in many Montana trout streams show brown trout mov- ing higher into watersheds. at trend might be reversed if the upper reaches of river systems fail to maintain flows conducive to brown trout spawning in the fall. Endangered bull trout are more dependent on very clean, cold water than westslope cutthroat. In many ways, bull trout are the best indicator of the health of coldwater streams. In addition to needing very cold, clean water in which to spawn, bull trout tend to migrate long distances during their life-cycle. As temperatures warm and sources of truly cold, clean water diminish, bull trout will lose more spawning habitat and the long stretches of connected habitat necessary for migration. ese trout concerns drive our organization's work. We are invested in and successful at protecting and restoring tributary streams that are the natal waters for native and wild trout, as well as the supplies of cold, clean water to our mainstem rivers. Our work has led to improvements in native and wild trout habitat and population numbers in systems like the Black- foot and Clark Fork Rivers. yea rs 3 IN ADDITION TO LOWER FLOWS, WARMER WATER TEMPERATURES, AND EARLIER AND LESS SPRING RUNOFF, TROUT POPULATIONS WILL BE AFFECTED BY DISEASES THAT THRIVE IN THOSE SAME CONDITIONS. ROBERT RATH

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