Trout in Emigration Creek

The Bonneville cutthroat trout (Oncorhynchus clarki utah) is the only native trout species to the state of Utah. They can be identified by the red, yellow, and orange markings on their lower jaw. The Bonneville cutthroat have more evenly distributed and larger spots than other trout species. It is a dull colored trout. The Bonneville cutthroat also has basibranchial teeth, which disappear when it hybridizes with other trout species.

The Rainbow trout (Oncorhynchus mykiss) is only native to the Pacific coast, but it has been successfully introduced throughout North America. The distinguishing marks on a rainbow trout vary from fish to fish but they all have a red or pink body stripe that appears when they spawn.

The Bonneville cutthroat is named for the great Pleistocene lake in which they originated. Lake Bonneville covered much of Utah during the last ice age. As the temperature increased the lake started to dry up. The salinity of the lake increased as it dried, and the trout took to the freshwater streams and lakes of the area. All that remains today of Lake Bonneville is the Great Salt Lake and the Bonneville Salt Flats. The Great Salt Lake is much too salty for the native trout species to survive in it.

Rainbow trout have been introduced to every continental state in the U.S. They have been widely introduced in Canada extending all the way into the Yukon Territory. They are also present in Mexico.

Like other cutthroat trout, the Bonneville cutthroat spawns in the spring. Spawning usually takes place when the water is between 43-59 degrees F. Trout change color when they are about to spawn. A female will seek out a slowly moving stretch of water. It is here that she will begin to build the redd, a nest for the eggs. She begins by lying on her side. She starts moving her tail back and forth causing gravel and other material to be moved out of the way. She keeps doing this until she has a redd that is four to six inches deep.

After the redd is finished the female swims over the top of the redd and waits for a male to join her. They deposit eggs and milt into the redd she has built, where fertilization will occur. The male swims off to the side and the female goes slightly downstream where she lays on her side and covers the redd with gravel, thus creating a new redd. The female may or may not use this new redd. A male and female are capable of repeating this process many times.

The eggs hatch in about three weeks at a temperature of about 54 degrees F. The newly hatched trout depend on their yolk sac for nourishment and as they grow the yolk sac slowly disappears.

The process of spawning is virtually the same for the Rainbow trout. Spawning is triggered by warmer water temperatures, which occur in spring from February to June. The amount of eggs a female lays is directly related to her size. Eggs should be incubated between 41 and 59 degrees F.

Trout will eat almost anything that will fit in their mouths. Since they are visual eaters, trout feed mostly at dawn and dusk when the light reflects off of the water allowing them to see their prey. In Emigration Creek, the trout eat segmented worms, snails, water striders, and mayfly and caddisfly nymphs and adults. A good source of food is also smaller, newly hatched fish, and terrestrial insects that fly close to the surface of the water or fall in and drown such as ants, wasps, and grasshoppers.

As part of a larger national study, an electro- shocking survey to census all fish in the stream from 1200 E. to 1300 E. (approximately 1/8 of a mile) was done by on September 15, 2000 by a U.S. Geological Survey Team. They found only 12 Rainbow trout in Emigration Creek. The results are given in the table below. This information is courtesy of U.S.G.S. biologist Elise Giddings.

Species of Trout	Total Length (inches)	Weight (g)
rainbow trout	6.96	54.0
rainbow trout	8.56	96.0
rainbow trout	10.4	182.0
rainbow trout	6.56	48.0
rainbow trout	9.20	138.0
rainbow trout	7.92	74.0
rainbow trout	10.6	203.0
rainbow trout	9.76	180.0
rainbow trout	4.16	180.0
rainbow trout	9.44	160.0

These data indicates that Emigration Creek fish are of different ages based on their length. We don't know if there is natural reproduction in the creek. Some may be sexually mature while others may have been hatched in the spring. Alternatively, the fish may have been recently introduced by Utah Division of Wildlife Resources, as part of an urban fishery program. However, rainbow trout have been "planted" in the creek at least two times during the past ten years by Westminster College. There have been recent, unconfirmed reports of the presence of Bonneville cutthroat trout in Westminster's section of the creek. Bonneville cutthroats are known to occur in the upper drainage of Parley's Creek and in Red Butte Creek drainages, but we are not aware of reports from the Emigration Creek watershed.

For more information on local hatcheries or fisheries, contact the Utah Division of Wildlife Resources:

The native Bonneville Cutthroat trout populations in almost all streams in Utah have hybridized extensively with the introduced Rainbow trout. When they hybridize, the basibranchial teeth of the cutthroat disappear. The hybrid trout individuals apparently compete for food and space resources and eventually the native species is displaced from their native stream habitats. There is a great deal of interest in analyzing the DNA of relict and hybrid populations of Bonneville cutthroat trout in Utah.

The chemical and physical characteristics of the water is also a big factor in determining whether the trout are able to survive. If the temperature becomes too warm or it lacks oxygen, they will disappear.