Theresa O’Halloran: On cutthroat trout
Cutthroat trout (oncorhynchus clarkii) is a species of freshwater fish in the salmon family. The name “cutthroat” refers to the distinct red color on the underside of the fish’s lower jaw. They are native to clear, cold rivers, lakes and ponds of western North America, and they are actually the only type of trout native to the state of Colorado.
This time of year, cutthroat trout begin spawning. Spawning is the reproductive process in which fish and other aquatic animals release eggs and sperm into the water. In Colorado, native cutthroat spawn in the spring during snowmelt when water temperatures reach 44-46 degrees. During this time, female cutthroat will locate a site with clean gravel and limited fine sediments to dig out a redd, or a nest, with her tail. The female will deposit her eggs in the finished redd and wait for a male to fertilize them with his sperm. Male cutthroats will often fight one another for the best spawning territory and will be seen with brilliant red coloring on their undersides. Unlike salmon, cutthroat trout and other trout species do not die after spawning and can participate in this reproductive process several times in their life.
Adaptations
Cutthroat trout, as well as other trout species, have special adaptations that help them survive in the wild. One adaptation of cutthroat is their great sense of smell. They have special holes called “nares” that help them smell different chemicals in the water. With their nares, cutthroat trout are able to distinguish between natural food and an angler’s artificial food. Cutthroat trout, as well as other fish species, are also able to use their talented noses to find their way back to their streams of origin. Another adaptation of cutthroat trout is their sight. Due to the position of their eyes on their bodies, trout have particularly good vision when they are looking up (but not when they are looking side to side). As a result, they can easily dodge predators, such as bears, birds and humans. They also have excellent close range vision and can see in color, so a fly-fisherman’s imitation fly won’t necessarily fool them. Lastly, cutthroat trout have excellent hearing. Trout have inner ears that allow them to hear like humans do. They also have special organs called “lateral lines” that allow them to feel sounds by picking up frequency vibrations through the water. These lateral lines help trout navigate underwater in order to find food, avoid obstacles and escape predators.
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Despite these admirable adaptations, the native cutthroat trout in Colorado have been unable to protect themselves from ecological change. Historically, there have been four subspecies of cutthroat trout found in Colorado. These are the Greenback cutthroat, Colorado River cutthroat, Rio Grande cutthroat and Yellowfin cutthroat. The Greenback cutthroat is native to the Arkansas and South Platte rivers. The Colorado River cutthroat is native to tributaries of the Green and Colorado rivers. The Rio Grande cutthroat is native to the Rio Grande River drainage in southern Colorado and New Mexico. The Yellowfin cutthroat, now extinct, was native to Twin Lakes.
Fate of Yellowfin
The fate of the Yellowfin cutthroat trout was a fate that was neither unexpected nor unique among Colorado’s cutthroats. Both habitat degradation and the introduction of non-native fish (particularly the introduction of rainbow, brown and brook trout in the late 1800s) have significantly diminished the historic ranges of Colorado’s cutthroat trout. Once widely distributed, cutthroat trout populations in Colorado are currently isolated to a limited number of headwater streams and lakes. All three remaining cutthroat subspecies are either currently listed or in the process of being listed under the Endangered Species Act.
This time of year during spawning, cutthroat trout are particularly sensitive to the disruptions that have occurred in their native habitats. Upstream vegetation loss by logging and livestock can increase sedimentation, which reduces oxygen absorption and overall survival of fertilized eggs. In addition, introduced non-native trout, including brook trout that spawn in the fall, will prey on the young immature cutthroats.
Fortunately, there have been collaborative efforts among state and federal resource agencies to develop and direct cutthroat recovery and conservation programs for each of the three remaining native species in Colorado. Thanks to their efforts, as well as increasing public awareness and support, we are still able to enjoy the presence of cutthroat trout in our streams, rivers and lakes.
Here on the Western Slope, you might be in for an adventure if you are looking for a Colorado River cutthroat trout. Look out for them in isolated headwater streams and lakes. If you are able to find a cutthroat with its bright red spawning colors, count yourself lucky. While there may be plenty of fish in the sea, there are definitely not plenty of cutthroat trout in Colorado.
Theresa O’Halloran is a naturalist at Walking Mountains Science Center.