Cutthroat Trout

Description

With such diversity of cutthroat trout subspecies, there are a wide range of spotting patterns and other observable characteristics that can make it difficult to differentiate between subspecies. That said, there are some generally observable traits that define a cutthroat. First, in cutthroat trout, the “cutthroat” mark on the lower edge of the jaw is typically bright red or orange, giving the appearance of a bleeding throat. Additionally, when compared with rainbow trout, cutthroat typically have larger black spots on their bodies that get denser (and more irregularly shaped) as you move towards the tail. Further, inland subspecies of cutthroat trout do not have significant spotting on the top of their heads, which rainbow trout and rainbow trout /cutthroat trout hybrids do.

Distribution

The cutthroat trout is the native trout species to much of the western U.S., with agreat deal of diversity owing to natural geographical boundaries that isolate many unique subspecies of cutthroat. While the universe of cutthroat trout subspecies is always evolving with new genetic research, most scientists recognize at least 10 distinct subspecies within western U.S. (link to https://westernnativetrout.org) In Colorado, there are at least three subspecies, including the Rio Grande cutthroat trout (native to the San Luis Valley), the Greenback cutthroat trout (native to the South Platte drainage), and the Colorado River cutthroat trout (native to the many Colorado River headwater streams and rivers). In fact, Colorado Parks and Wildlife (the fish and wildlife management agency in Colorado) recently discovered a unique lineage of cutthroat trout.

Biology

Cutthroat trout are spring spawners, and they will initiate spawning in response to warming water temperatures and increasing daylight hours. Once eggs have been put down in the gravel, it takes about a month for the eggs to hatch, and another 3 weeks or so for the juvenile cutthroat trout to emerge from the redd. Interestingly, while cutthroat trout are typically better cold-adapted than other trout (e.g. rainbow and brown trout), stream temperatures can sometimes be too cold for natural reproduction to occur if the window from hatch to the onset of winter is too brief for those juvenile trout to build sufficient energy stores to survive the winter. In small streams with limited food, cutthroat trout rarely live longer than 3-4 years, but in bigger waters (particularly high mountain lakes), they can live much longer and get much larger because the cold temperatures lower their metabolic rate for much of the year. The feeding habits of cutthroat trout are similar to other trout species in similar habitats, in that they largely rely on eating insects for much of their lives, but may become piscivorous as they get larger.

Conservation

Throughout the western U.S., the cutthroat trout has been extirpated from much of its native range due to human causes such as pollution (e.g. mining), deforestation, and stocking of non-native fish. In Colorado, all subspecies of cutthroat trout occupy less than 15% of their historic distributions. Regarding non-natives, cutthroat do not typically compete well with brook and brown trout, and due to the similar timing with rainbow trout spawning, they can hybridize and dilute the cutthroat trout genetics within the population over time. As such, to be viable populations over time, cutthroat trout need to be physically isolated from non-native trout species via a barrier, natural (e.g. a significant waterfall) or man-made. Another major looming threat for cutthroat trout is climate change. As noted above, cutthroat thrive within a relatively narrow range of water temperatures, and so some habitats may becometoo warm (or dry) in an uncertain climatic future. Fortunately, Colorado has many watersheds that are currently much colder than what is stressful or lethal for cutthroat trout, and so all future reintroductions of cutthroat should target large watersheds that have adequately cold temperatures and ample streamflow to buffer the effects of climate change. One great example of this is work is the reclamation work that is happening in the Great Sand Dunes National Park and Preserve for Rio Grande cutthroat trout.