Rainbow Trout: Global Invaders (Part 2 of 2)

June 2019

This year there was a bounty on rainbow trout in the South Fork of the Snake River in southeastern Idaho. The river, known for its robust native population of cutthroat trout, is one of the last strongholds for Snake River/Yellowstone cutthroat trout in the Rockies. But hybridization between native cutthroat and rainbows threatens the genetic makeup of cutthroat, so much so that Idaho Fish and Game are electroshocking and removing rainbow trout completely. Anymore, this situation is not uncommon. Though rainbows are desirable as a hatchery species, rainbow trout are also invaders. They are more adept at foraging and more aggressive than many other species where they are introduced, interbreed-and-hybridize with cutthroat trout, and prey on native fish and invertebrates.

Additionally, as Man’s (aquatic) Best Friend, they have followed us around the world. Rainbow trout are now common across the globe, found on every continent except Antarctica. As scientists have started to recognize the largely destructive effects rainbow trout have on native ecosystems, they are now considered a global biodiversity threat. The International Union for the Conservation of Nature (IUCN, a leading organization in biodiversity protection) has black-listed rainbow trout as #63 of the top 100 most invasive alien species in the world. (If you were curious, brown trout also make the list at #82). There are even some places where the presence of rainbow trout simply isn’t tolerated. Some lakes in the High Sierras have lost populations of native frogs from trout predation. The trout were so good at eating the frogs that simply finding fish in a lake was a strong indication no native frogs would be present. Still, rainbow trout are proliferated and introduced to lakes, and streams, in hopes of bringing in revenues for fisheries programs.

So exists a disconnect between the angler’s expectations for what freshwater conservation should be, and what scientists might suggest. Enhancing coldwater fisheries doesn’t always coincide with protecting biodiversity. As anglers, we need to acknowledge that rainbows (and browns) are here to stay, but just don’t require the same special attention as native species. These native species are what makes ecosystems unique, and fun to explore. Here in the Western United States, we have multiple treasured watersheds with native cutthroat trout and endangered fish. Let’s try to keep these places as they are, free from the global invaders. After all, the trout-angling world wouldn’t be as exciting if all we had was a world full of genetically tailored rainbow trout.

Sources:

• Wright, S. 2019. Keeping Rainbow Trout Out of the South Fork Snake River. Boise State Public Radio. https://www.boisestatepublicradio.org/environment/2019-06-05/keeping-rainbow-trout-out-of-the-south-fork-snake-river
• Global Invasive Species Database. 2013. 100 of the World’s Worst Invasive Alien Species. http://www.iucngisd.org/gisd/100_worst.php
• Williams, T. 2015. Purging Trout to Save Frogs. The National Wildlife Federation. https://www.nwf.org/Magazines/National-Wildlife/2015/AugSept/Conservation/Trout-Versus-Frogs
• Invasive Species Initiative. Accessed 2021. Rainbow Trout. Crawford, S. Muir, A. 2007. Global introductions of salmon and trout in the genus Oncorhynchus: 1870-2007. Review in Fish Biology and Fisheries. 18. https://link.springer.com/article/10.1007/s11160-007-9079-1
• Muhlfeld C. et al. 2019. Global Status of Trout and Char: Conservation Challenges in the Twenty-First Century. American Fisheries Society.