The Brown Trout (Salmo Trutta) is torpedo shaped with a typically brassy brown color on top, fading to a creamy or golden belly. The brown spots are mainly on the head, upper body and dorsal fin, but do not extend into the tail. About halfway down the sides the spots often have a lighter color halo and some of those spots will be red. The spots do not extend down onto the belly.
Brown Trout are commonly 12 to 20 inches long and weigh a couple pounds. The Montana state record Brown Trout weighed 29 pounds and last year a new world record Brown Trout was caught in Michigan and tipped the scales at over 41 pounds. They can live to an age of 20 years.
Coming to North America
While the Brown Trout is mainly a freshwater species, some will migrate to the sea and spend much of its life there and then return to freshwater to spawn. Of those that migrate from the sea, only a small percent will be able to repeat the cycle.
The ones that live in lakes usually move into streams to spawn in the fall. Brown Trout are considered to be native to Europe and western Asia and were widely introduced to North America in 1883 and in 1889 to the Madison River, a prime trout stream flowing west out of Yellowstone National Park and then north to help form the Missouri River.
The results of plant, fish or animal introductions are not always seen favorably. It is usually long after the fact that we become aware of the consequences. Today, keeping native ecosystems whole and free of invasive species is seen as the best way to keep those communities healthy.
Warm water temperatures can cause a reduction of dissolved oxygen levels which can cause fish kills. The trout need to be able to get to turbulent, more oxygenated water. Water pollution and field wash from agricultural fertilizers can increase habitat problems.
Awareness of the potential problems led to efforts to overcome them. Submerged rocks, undercut banks and overhanging vegetation provide protection from predators, sunlight and warmer temperatures.
Brown Trout are active during both day and night and feed when the opportunity arises. They feed on invertebrates off the bottom, other fish, frogs, mice, birds and insects flying just above the water’s surface. The high portion of insect larvae, pupae, nymphs and adults in their diet is why the flies of fishermen are made to imitate these food sources. Caddis, stonefly and mayfly are among the favorite flies used locally. The artificial fly must also be made to imitate the appropriate behavior to be most successful. Why do some fishermen have all the luck?
In The Bighorn
Well, it is not just luck. Fishing in the Bighorn River helps because it is one of the best trout streams in the country. In 1987, trout populations reached a record high of almost 11,000 trout per mile. In 1997, new records were established with 2,300 rainbow trout per mile and 8,800 brown trout per mile.
However in the height of the drought in 2003, brown trout set record lows of only 492 per mile and not enough rainbows were recaptured to make valid population estimates. Higher water years have helped populations start a comeback, but more good water years are needed to return the Bighorn River to a world class fishery.