The brook trout (Salvelinus fontinalis) is a species of freshwater fish in the salmon family Salmonidae. It is native to Eastern North America in the United States and Canada, but has been introduced elsewhere in North America and to additional continents. In parts of its range, it is additionally known as the eastern brook trout, speckled trout, brook charr, squaretail, or mud trout, amongst others.[3] A potamodromous population in Lake Superior is known as coaster trout or, simply, as coasters. The brook trout is the state fish of nine states: Michigan, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Vermont, Virginia, and West Virginia, and the Provincial Fish of Nova Scotia in Canada.

Systematics and taxonomy

The brook trout was first scientifically described as Salmo fontinalis by the naturalist Samuel Latham Mitchill in 1814. The specific epithet "fontinalis" comes from the Latin for "of a spring or fountain", in reference to the clear, cold streams and ponds in its native habitat. The species was later moved to the char genus Salvelinus. Though commonly called a trout, the brook trout is thus actually one of the chars, which in North America additionally include the lake trout, bull trout, Dolly Varden, and the Arctic char.

There is little recognised systematic substructure in the brook trout, but two subspecies have been proposed. On the additional hand, three ecological forms are distinguished.

Subspecies

The aurora trout, S. f. timagamiensis, is a subspecies native to two lakes in the Temagami District of Ontario, Canada.[4] The silver trout, (Salvelinus agassizii or S. f. agassizii), is an extinct trout species or subspecies last seen in Dublin Pond, New Hampshire, in 1930.[5] It is considered by fisheries biologist Robert J. Behnke as a highly specialised form of brook trout.

Ecological forms

Robert J. Behnke describes three ecological forms of the brook trout. A large lake form evolved in the larger lakes in the northern reaches of its range and are ordinarily piscivorous as adults. A sea-run form that migrates into saltwater for short periods of time to feed evolved along the Atlantic coastline. Finally, 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 in (30 cm) or lives for more than three years. All three forms have the same general appearance.

Hybrids

The brook trout produces hybrids both with its congeners Salvelinus namaycush and Salvelinus alpinus, and intergeneric hybrids with Salmo trutta.[7]

The splake is an intrageneric hybrid between the brook trout and lake trout (S. namaycush). Although uncommon in nature, they're artificially propagated in substantial numbers for stocking into brook trout or lake trout habitats.[8] Although they're fertile, back-crossing in nature is behaviorally problematic and quite little natural reproduction occurs. Splake grow more than brook trout and become piscivorous sooner and are more tolerant of competitors than brook trout.[2]

The tiger trout is an intergeneric hybrid between the brook trout and the Eurasian brown trout (Salmo trutta). Tiger trout occur quite rarely naturally, but are at times artificially propagated. Such crosses are almost always reproductively sterile. They are popular with a large number of fish-stocking programmes because they can grow quickly, and might help keep rough fish populations in cheque due to their highly piscivorous (fish-eating) nature.[2]

The sparctic char is an intrageneric hybrid between the brook trout and the Arctic char (S. alpinus).[11]

Description

The brook trout has a dark green to brown color, with a distinctive marbled pattern (called vermiculation) of lighter shades across the flanks and back and extending at least to the dorsal fin, and most often to the tail. A distinctive sprinkling of red dots, surrounded by blue halos, occurs 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 quite red or orange when the fish are spawning.

Typical lengths of the brook trout vary from 25 to 65 cm (9.8 to 25.6 in), and weights from 0.3 to 3 kg (0.66 to 6.61 lb). The maximum recorded length is 86 cm (34 in) and maximum weight 6.6 kg (15 lb). Brook trout 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. 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 instance, in spring, growth increased with temperature at a faster rate with high flow rates than with low flow rates.[2]

Range and habitat

Brook trout are native to a wide area of Eastern North America, but are 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 LakesSaint 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 streams 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. throughout the late nineteenth and early 20th centuries 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,[11] in Argentina[2] and New Zealand.[2] Although not all introductions were successful, a great a large number of established wild, self-sustaining populations of brook trout in non-native waters.

Habitat

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 like 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.[2] Water temperatures ordinarily range from 34 to 72 °F (1 to 22 °C). Warm summer temperatures and low flow rates are stressful on brook trout populations—especially larger fish.[2]

Coasters

A potamodromous population of brook trout native to Lake Superior, which migrate into tributary rivers to spawn, are called "coasters".[3] Coasters tend to be larger than most additional populations of brook trout, most often reaching 6 to 7 lb (2.7 to 3.2 kg) 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.[24]

Salters

When Europeans first settled Eastern North America, semianadromous 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 might 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 salt water, salters gain a more silvery color, losing much of the distinctive markings seen in freshwater. Notwithstanding within two weeks of returning to fresh water, they assume typical brook trout colour and markings.

Ecology and reproduction

Diet

Brook trout have a diverse diet that includes larval, pupal, and adult forms of aquatic insects (typically caddisflies, stoneflies, mayflies and aquatic dipterans), and adult forms of terrestrial insects (typically ants, beetles, grasshoppers and crickets) that fall into the water, crustaceans, frogs and additional amphibians, molluscs, smaller fish, invertebrates, and even small aquatic mammals like voles.

Reproduction

The female constructs a depression in a location in the stream bed, at times referred to as a "redd", where groundwater percolates upward through the gravel. One or more males approach the female, fertilising the eggs as the female expresses them. A majority of spawnings involve peripheral males which directly influences the number of eggs that survive into adulthood. In general, the larger the number of peripheral males present, the more likely the eggs will be cannibalized.[3] 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.

Angling

The brook trout is a popular game fish with anglers, particularly fly fishermen.

Until it was displaced by introduced brown trout (1883) and rainbow trout (1875), the brook trout attracted the most attention of anglers from colonial times through the first 100 years of U.S. history. Sporting writers like Genio Scott Fishing in American Waters (1869), Thaddeus Norris American Anglers Book (1864), Robert Barnwell Roosevelt Game Fish of North America (1864) and Charles Hallock The Fishing Tourist (1873) produced guides to the best-known brook trout waters in America. As brook trout populations declined in the mid-19th century near urban areas, anglers flocked to the Adirondacks in upstate New York and the Rangeley lakes region in Maine to pursue brook trout. In July, 1916 on the Nipigon River in northern Ontario, an Ontario physician, John W. Cook, caught a 14.5 lb (6.6 kg) brook trout which stands as the world record.

Today, a large number of anglers practise catch-and-release tactics to preserve remaining populations, and organisations like Trout Unlimited have been in the forefront of efforts to institute air and water quality standards sufficient to protect the brook trout. Revenues derived from the sale of fishing licences have been used to restore a large number of sections of creeks and streams to brook trout habitat.[28]

The current world angling record brook trout was caught by Dr. W. J. Cook on the Nipigon River, Ontario, in July 1915. The 31 in (79 cm) trout weighed only 14.5 lb (6.6 kg) because, at the time of weighing, it was badly decomposed after 21 days in the bush without refrigeration. [3] A 29 in (74 cm) brook trout, caught in October 2006 in Manitoba, isn't eligible for record status after it was released alive.[4] This trout weighed about 15.98 lb (7.25 kg) based on the accepted formula for calculating weight by measurements, and it currently stands as the record brook trout for Manitoba.[4]

Artificial propagation and aquaculture

Brook trout are additionally commercially raised in large numbers for food production, being sold for human consumption in both fresh and smoked forms.[4] Due to its dependence on pure water and a variety of aquatic and insect life forms, the brook trout is additionally used for scientific experimentation in assessing the effects of pollution and contaminated waters.

Conservation 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 a large number of watercourses as land development, forest clear-cutting, and industrialization took hold.[33] Streams and creeks that were polluted, dammed, or silted up most often became too warm to hold native brook trout, and were colonised by transplanted smallmouth bass and perch or additional introduced salmonids like 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 quite susceptible to damage by the introduction of exogenous species. Many lacustrine populations of brook trout have been extirpated by the introduction of additional species, particularly percids, but at times additional spiny-rayed fishes.

In addition to chemical pollution and algae growth caused by runoff containing chemicals and fertilizers, air pollution has additionally 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 a few Appalachian streams and creeks.[4] 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.[4] Today, in a large number of parts of the range, efforts are underway to restore brook trout to those waters that once held native populations, stocking additional trout species only in habitats that can no longer be recovered sufficiently to sustain brook trout populations.

Organizations like Trout Unlimited and Trout Unlimited Canada[24] are partnering with additional organisations like the Southern Appalachian Brook Trout Foundation,[4] the Eastern Brook Trout Joint Venture,[4] and state, provincial, and federal agencies to undertake projects that restore native brook trout habitat and populations.

As an invasive species

Although brook trout populations are under stress in their native range, they're considered an invasive species where they have been introduced outside their historic native range.[4][4][5] In the northern Rocky Mountains, non-native brook trout are considered a significant contributor to the decline or extirpation of native cutthroat trout (Oncorhynchus clarki) in headwater streams.[5] Non-native Brook trout populations have been subject to eradication programmes in efforts to preserve native species.[5][5] In Yellowstone National Park, anglers might take an unlimited number of non-native brook trout in a few drainages. In the Lamar River drainage, a mandatory kill regulation for any brook trout caught is in effect.[44] In Europe, introduced brook trout, once established, have had negative impacts on growth rates of native brown trout (S. trutta).[11]