Markings and Coloration
The brook trout can be recognized by the wavy lines, or vermiculations, on its dark, olive-green back–the same pattern created when the sun shines through rippled water to cast shadows on the bottom. The result is a camouflage enabling the brook trout to avoid predators from above such as kingfishers and herons.
The brook trout also typically has many pale yellow spots and a few small red spots surrounded by blue halos on their sides. They’ve also been described as the only trout with light spots against a dark background, as the brown and rainbow trout have the opposite spotting pattern (dark spots on a paler background).
The brook trout’s pectoral, ventral, and anal fins are starkly edged in white, which again is unique among other common trout. The white is the main giveaway. Even when the brook is motionless, the white-edged fins will call your attention to the fish. The highly visible, white-edged fins are a definite disadvantage when it comes to the brook’s predators.
Another characteristic is a relatively large head and mouth, and the head may amount to one quarter of the body length on adult fish.
During their fall spawning period, the lower flanks of males become brilliant orange and older males may develop a slightly hooked lower jaw.
If you are still in doubt after checking all the previous characteristics, feel along the center of the mouth’s roof with your fingertip. The vomerine bone has teeth in a small cluster at its forward end. If you find teeth all along the roof of the mouth, you didn’t catch a “brookie”.
Because the brook trout is deep bodied in proportion to it’s length, it can swim efficiently in water as shallow as their body depth. Their maneuverability is an asset in capturing a wide variety of foods in waters of all depths. The powerful, long run of a large rainbow or brown when first hooked is almost always absent with large brook trout, which tend to a bull-dog tugging and twisting fight near the bottom. Such a fight is part of their nature, determined in turn largely by their shape.
Brook trout prefer cold, clear streams and are the most cold tolerant of all common trout.
Brookie Range and Habitat
As a general case, brooks are native to the northern half of the eastern United States in addition to eastern Canada. There are some brook-trout populations as far south as Georgia along the Appalachian spine, but these have been in decline since at least 1900 and probably earlier, when both logging and overfishing destroyed trout habitat at lower elevation and the more accessible areas of highland streams. In Great Smoky Mountain National Park on the Tennessee-North Carolina border, where log-ging was essentially eliminated with the park’s establishment in 1936, brook-trout populations have continued to decline. The apparent cause is competition from rainbow trout that were first introduced to this area in 1910 and are slowly displacing the remaining brook trout higher and higher into the region’s headwater streams. These head-water areas could be the brook trout’s last refuge here as the rainbows’ upstream movement may be finally limited by physical barriers such as waterfalls or other obstacles created by Park personnel on behalf of the brook trout.
Brook trout are inherently cold-water fish, and can perform well within a temperature range of 40 to 68 degrees Fahrenheit. However, brook trout have been shown to feed at temperatures as low as 34 degrees, and the lethal temperature limit of the brook seems to be around 30 degrees.
The upper limit of a brook trout’s tolerance is somewhere between 72 and 77 degrees, which is often reached in the middle and southern portions of its range in late summer. However, to feed or avoid a predator the brook might venture briefly into warmer water–but not for long.
Where rainbows are more open-water oriented than brook trout and depend on insects at or near the lake’s surface, brook trout typically feed more at a stream’s bottom.
Few brook trout survive to age four in the wild, so are generally the shortest lived trout. The growth of the brook trout varies, depending on such things as habitat, water temperature, and competition from other fish. Even in productive waters, the brook will rarely weigh more than 3 pounds by the end of their third year.
Brook trout at spawning time appear to be severely stressed by the catch-and-release process. The implication is that they should be left unmolested at this season, even though catch-and-release rules on some brook-trout waters permit year-round fishing.
The restoration efforts of Park resource managers have led them to closing some streams and tributaries to all fishing, and ensuring natural barriers such as waterfalls are adequate to prevent the brown and rainbow trout from migrating upstream.