Oncorhynchus clarki behnkei
A Snake River Finespotted Cutthroat from a small high gradient stream in the Rockies.
The Snake River fine spotted cutthroat is native to the Snake River drainage between Jackson Lake and the Palisades Reservoir in Wyoming. Above and below this area the predominant fish is the Yellowstone cutthroat, however what is odd is that before the construction of the dam on Jackson Lake and Palisades Reservoir, there were no barriers to isolate the two types of cutthroat from each other. It is thought that the fine spotted form of cutthroat diverged from the Yellowstone cutthroat during the last ice age when it likely was isolated in the Snake River (Behnke 1992). Modern genetic testing is unable to differentiate between the large spotted Yellowstone cutthroat and fine spotted and further supports this recent divergence of the two subspecies (Loudenslager and Kitchin 1979; Novak et al. 2005). The Snake River fine spotted cutthroat can attain sizes in excess of 20 inches and 3 pounds and are known for their fighting ability.
Snake River finespotted cutthroat occur as lacustrine, fluvial and stream resident populations. The fluvial component is the most widespread life history form of this trout and is found in the Snake River and its larger tributaries between Jackson Lake and Palisades Reservoir. These fish typically reach sexual maturity at three to four years of age, with about ten percent of a given spawning run being composed of five or six year old repeat spawners (Trotter 2008). River dwelling populations of these trout may spawn within the main channel of the river or make migrations up tributaries to spawn. In the Snake River itself spawning success is limited due to high spring flows and sediment loads, which has led to spring fed tributary streams being predominately used for spawning (Kiefling 1978). Fish in the Salt River drainage typically migrate to spring feed tributaries between March and June (Joyce and Hubert 2004) and similar patterns have been seen in the Snake River. Spawning generally occurs in riffles less than a foot deep to provide eggs with enough oxygen to survive. After spawning the mortality rate is about fifty percent but is offset by a higher than usual survival rate for the eggs (Trotter 2008).
Young of year trout typically utilize slower moving stream margins with cover as habitat until the are big enough to establish territories for themselves (Hubert and Joyce 2005). By age one and at a size of about four inches the juvenile migrate to the main river. Once in the riverine environment the growth rate for finespotted cutthroat is fast and by age three they typically reach a size of 11 to 14", about a 20% faster growth rate that that of the cutthroat in Yellowstone Lake (Trotter 2008). Snake River finespotted cutthroat feed primarily on aquatic and terrestrial insects until they reach an age of three, at which time they begin to feed heavily on fish as well. As fall progresses into winter and water temperatures drop the metabolic rate of trout drops and feeding and growth are greatly diminished. Finespotted cutthroat in the mainstem Snake River respond to these temperature drops by seeking out pool habitat for overwintering until temperatures rise about 34 degrees Fahrenheit, at which point they begin to utilize runs more (Harper and Farag 2004).
There are a number of lakes and ponds throughout the range of the Snake River finespotted cutthroat, which support lacustrine populations of these fish. These fish exhibit a similar life history to that of other lake dwelling cutthroat populations with adults requiring tributary streams as spawning habitat. When stocked in lakes outside their native range finespotted cutthroat show an incredible ability to adapt to a wide variety of environments and food sources. Stream resident populations of finespotted cutthroat occur in many spring creeks as well as higher gradient tributaries to the Snake River. These fish exhibit similar food source preferences and spawning times as fluvial individuals. It appears that this subspecies may not be as well adapted to high gradient mountain streams others are, as introductions to this type of habitat have not fared as well as would be expected (Mullan 1975
Out of all of the subspecies of cutthroat, the finespotted is perhaps doing better than any of the others. Today it is still the dominant trout throughout most of its native range, which may be partially due to the fact that finespotted cutthroat do not readily hybridize with rainbow trout. However it is thought that some of this resistance to hybridization and the habitat partitioning between the large and finespotted forms of cutthroat may be breaking down. This has been indicated in recent years by an increasing amount of cutthroat with an intermediate sized spotting pattern found in the Snake River and its tributaries (Novak et al. 2005). Also where brook trout have been introduced to high gradient mountain streams they have replaced the native finespotted cutthroat. In the Snake River system habitat alterations have also had an impact on the cutthroat. While a large portion of the river lies within the boundaries of Grand Teton National Park, farming, logging and dams have had an impact on the drainage. The construction of the dam on Jackson Lake has been shown to have impacted the dynamics of the river system, but reducing flood activity and natural channel movement (Marston et al. 2005). Critical spawning habitat on spring creeks has also been impacted by channelization and increased sediment loads. Efforts have are currently being made to restore degraded stream habitat throughout the basin and the cutthroat appear to be responding positively.
Today the Snake River finespotted cutthroat is the most widely stocked subspecies of cutthroat and as such are found well outside of their native range. Part of the success of these introductions is due to their coexistence with numerous prey species in the Snake River, which allows the finespotted cutthroat readily adapt to new environments (Behnke 2002). Beyond this studies have shown that finespotted cutthroat also have a greater resistance to whirling disease than other subspecies of cutthroat or rainbow trout (Sipher and Bergersen 2005). This coupled with the fact that they grow fast and can attain relatively large sizes makes them a popular choice with fisheries agencies
The trait that makes Snake River fine spotted cutthroat so unique is their spots, which are smaller than those of any other type of trout in western North America. These spots typically look like a sprinkling of pepper and are profusely distributed across the body with the highest concentration towards the caudal peduncle. The coloration of the lower fins on fine spotted cutthroat typically varies from that of the Yellowstone cutthroat and are more of a deep red or orange color. Most of their other traits tend to be similar to Yellowstone cutthroat, with brownish yellow, greenish bronze or even a silvery coloration. The gill plates are generally an orangish-pink coloration and they have reddish-orange cutthroat marks below the lower jaw.
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