Brook trout

Appearance

Fisheries biologist Robert Behnke describes three forms of the brook trout. A large lake form evolved in the larger lakes in the northern reaches of it range and is generally piscivorous as adults. A sea-run form that migrates into salt-water for short periods of time to feed evolved along the Atlantic coastline. Finally, Behnke describes a smaller generalist form that evolved in the small lakes, ponds, rivers and streams throughout most of the original native range. This generalist form rarely attains sizes larger than 12 inches or lives for more than 3 years. All three forms have the same general appearance. The brook trout has a dark green to brown color, with a distinctive marbled pattern of lighter shades across the flanks and back and extending at least to the dorsal fin, and often to the tail. A distinctive sprinkling of red dots, surrounded by blue haloes, occur along the flanks. The belly and lower fins are reddish in color, the latter with white leading edges. Often, the belly, particularly of the males, becomes very red or orange when the fish are spawning.

The species reaches a maximum recorded length of 86 cm and a maximum recorded weight of 6.6 kg . It can reach at least seven years of age, with reports of 15 year old specimens observed in California habitats to which the species has been introduced. Typical lengths vary from 25 to 65 cm , and weights vary from 0.3 to 3.0 kg . Growth rates are dependent on season, age, water and ambient air temperatures, and flow rates. In general flow rates affect the rate of change in the relationship between temperature and growth rate. For example in spring growth increased with temperature at a faster rate with high flow rates than with low flow rates.

Naming

* Aurora trout, , is a subspecies native to two lakes in the Temagami District of Ontario, Canada.

⤷  Silver trout, , is an extinct trout species last seen in Dublin Pond, New Hampshire, in 1930. Considered by fisheries biologist Robert J. Behnke as a highly specialized form of brook trout.Although brook trout populations are under stress in their native range, they are considered an invasive species where they have been introduced outside their historic native range.

Status

Brook trout populations depend on cold, clear, well-oxygenated water of high purity. As early as the late 19th century, native brook trout in North America became extirpated from many watercourses as land development, forest clear-cutting, and industrialization took hold. Streams and creeks that were polluted, dammed, or silted up often became too warm to hold native brook trout, and were colonized by transplanted smallmouth bass and perch or other introduced salmonids such as brown and rainbow trout. The brown trout, a species not native to North America, has replaced the brook trout in much of the brook trout's native water. Brook trout populations, if already stressed by overharvest or by temperature, are very susceptible to damage by the introduction of exogenous species. Many lacustrine populations of brook trout have been extirpated by the introduction of other species, particularly percids, but sometimes other spiny-rayed fishes.

In addition to chemical pollution and algae growth caused by runoff containing chemicals and fertilizers, air pollution has also been a significant factor in the disappearance of brook trout from their native habitats. In the U.S., acid rain caused by air pollution has resulted in pH levels too low to sustain brook trout in all but the highest headwaters of some Appalachian streams and creeks. Brook trout populations across large parts of eastern Canada have been similarly challenged; a subspecies known as the aurora trout was extirpated from the wild by the effects of acid rain. Today, in many parts of the range, efforts are underway to restore brook trout to those waters that once held native populations, stocking other trout species only in habitats that can no longer be recovered sufficiently to sustain brook trout populations.

Habitat

Brook trout are native to a wide area of eastern North America, but increasingly confined to higher elevations southward in the Appalachian Mountains to northern Georgia and northwest South Carolina, Canada from the Hudson Bay basin east, the Great Lakes–Saint Lawrence system, the Canadian maritime provinces and the upper Mississippi River drainage as far west as eastern Iowa. Their southern historic native range has been drastically reduced, with fish being restricted to higher elevation, remote steams due to habitat loss and introductions of brown and rainbow trout. As early as 1850, the brook trout's range started to extend west from its native range through introductions. The brook trout was eventually introduced into suitable habitats throughout the western U.S. during the late 19th and early 20th century at the behest of the American Acclimatization Society and by private, state and federal fisheries authorities. Acclimatization movements in Europe, South America and Oceania resulted in brook trout introductions throughout Europe, in Argentina and New Zealand. Although not all introductions were successful, a great many established wild, self-sustaining populations of brook trout in non-native waters.The brook trout inhabits large and small lakes, rivers, streams, creeks and spring ponds. They prefer clear waters of high purity and a narrow pH range and are sensitive to poor oxygenation, pollution and changes in pH caused by environmental effects such as acid rain. The typical pH range of brook trout waters is 5.0 to 7.5, with pH extremes of 3.5 to 9.8 possible. Water temperatures typically range from 34 to 72°F . Warm summer temperatures and low flow rates are stressful on brook trout populations—especially larger fish. Brook trout have a diverse diet that includes larval, pupal and adult forms of aquatic insects , and adult forms of terrestrial insects that fall into the water, crustaceans, frogs and other amphibians, molluscs, smaller fish, invertebrates and even small aquatic mammals such as voles.

The female constructs a depression in a location in the stream bed, sometimes referred to as a "redd", where groundwater percolates upward through the gravel. One or more males approaches the female, fertilizing the eggs as the female expresses them. A majority of spawnings involve peripheral males which directly influences the amount of eggs that survive into adulthood. In general the larger the number of peripheral males present the more likely the eggs will be cannibalized. The eggs are slightly denser than water. The female then buries the eggs in a small gravel mound; they hatch in 95 to 100 days.

Coasters

A potamodromous population of brook trout native to Lake Superior, which run into inflowing rivers to spawn, are called "coasters". Coasters tend to be larger than most other populations of brook trout, often reaching 6 to 7 pounds in size. Many coaster populations have been severely reduced by overfishing and habitat loss by the construction of hydroelectric power dams on Lake Superior tributaries. In Ontario and Michigan, efforts are underway to restore and recover coaster populations.

Salters

When Europeans first settled eastern North America, semi-anadromous or sea-run brook trout, commonly called "salters" ranged from southern New Jersey, north throughout the Canadian maritime provinces and west to Hudson Bay. Salters may spend up to three months at sea feeding on crustaceans, fish and marine worms in the spring not straying more than a few miles from the river mouth. The fish return to freshwater tributaries to spawn in the late summer or autumn. While in saltwater, salters gain a more silvery color, losing much of the distinctive markings seen in freshwater. However, within two weeks of returning to freshwater, they assume typical brook trout color and markings.

Cultural

Brook trout are also commercially raised in large numbers for food production, being sold for human consumption in both fresh and smoked forms. Because of its dependence on pure water and a variety of aquatic and insect life forms, the brook trout is also used for scientific experimentation in assessing the effects of pollution and contaminated waters.