Natural History of the
Brook Trout (Salvelinus fontinalis)

Salvelinus fontinalis
illustration by Ellen Edmonson from "A Biological Survey of the Champlain Watershed" (1930)
 

Brook Trout are born in cold freshwater streams. As they mature they may move down into larger streams or into coldwater lakes. The life cycle is completed when the adult fish move upstream again to reproduce by spawning. In a few populations along the coast the Brook Trout may move into saltwater as they mature. These populations are anadromous just like the Atlantic Salmon.

Life Cycle: Brook Trout Life Cycle

During the summer months adult Brook Trout are usually found in larger streams and lakes. In late summer and early fall as the length of the day begins to shorten the Brook Trout begin to migrate out of the lakes and up the larger streams into the smaller headwater steams. Here they seek out a spawning location in gravel beds in streams with cold, well-oxygenated water. Brook Trout seem to seek out areas where upwelling springs occur. The streams are usually fairly shallow, but not so shallow that the bed will be damaged by ice during the winter. Some Brook Trout may remain in lakes and spawn in gravel beds over upwelling springs.

Spawning usually begins in October and continues into the fall. In New York the peak of the spawning is in November. In spawning the female Brook Trout prepares a depression in the gravel of the stream using her tail fin. This depression is called the redd. Hovering over the redd the female releases 15-60 pea sized eggs into the redd. As the eggs settle into the redd the male, who hovers nearby, releases a cloud of sperm, or milt, and the eggs are fertilized. The female then uses her tail fin to sweep the gravel back over the eggs and then moves on to construct another redd. The total number of eggs a female lays depends on her size, larger females laying more eggs. A half pound female will usually lay about 400-600 eggs.

Brook Trout are not genetically programmed to die after spawning as are the Pacific species of salmon. Spawning is however difficult and dangerous and many fish do die during spawning.

The length of the incubation period varies according to the temperature - at lower temperatures the incubation period is longer. For example, in 35 Fº water, the incubation period is about 144 days; in 50 Fº water, the incubation is only 44 days. The effect of temperature on the length of the incubation period is adaptive. No matter when during the fall/winter the eggs are laid, it allows the eggs to hatch in March and April when food for the larvae becomes abundant.

Newly hatched trout are referred to as alevin. They somewhat resemble tadpoles because of the pendulous yolk sacs protruding from their undersides. Alevin remain in the protective gravel of the redd as they use up the stored nutrients in the yolk sac.

When the nutrients are gone the young salmon emerge ("swim-up") from the gravel. At this stage they are referred to as fry. The fry leave the redd area and move to shallow water where they can find some protection from predators. After several weeks a series of dark vertical bands called parr marks appear along the sides of the young trout and they are now referred to as parr. The Brook Trout lose these marks as they grow, eventually becoming juveniles, then adults.

Prey and Predators:

Brook Trout will eat almost any small animal they can get in their mouths. They are carnivores and they are opportunistic. As tiny fry they feed mainly on microscopic crustaceans and then later on small insect larvae. As parr they begin to feed on mid-sized insect larvae such as mayfly or caddis fly larvae. As juveniles they begin to include larger insect larvae, and as young adults begin to feed on small fish. Larger adults feed mainly on fish such as minnows and sculpins. A complete list of what they eat is essentially a list of everything that is available. Brook Trout are cannibals and often eat smaller members of their species.

Because they use eyesight to hunt their prey, most feeding takes place during the day, especially in the early morning. On nights when the moon is bright, feeding may also take place at night.

The Brook Trout are themselves food for many predators. Larger fish, especially larger Brook Trout, are the most important predator. Other predators include river otters, herons, and kingfishers.

Brook Trout Decline and Restoration:

Brook Trout originally lived in northeastern North America, as far south as Georgia in the Appalachian Mountains, as far north as arctic Canada, and as far west as the upper midwest. The onset of land clearing for lumber and for agriculture in the 1700's, and especially in the 1800's, meant the beginning of hard times for Brook Trout. There were three main factors that led to the decline in both the ranges of the Brook Trout and in the numbers found in the areas where they were still present:

Attempts to restore the Brook Trout have proceeded in two ways: 1) As a part of a general drive to reduce pollution in the nation's waters; 2) And by controlling the number of fish removed by anglers and at the same time adding additional fish raised in hatcheries.

Much of the emphasis in controlling the amount of pollution reaching our rivers and streams has been to reduce the amounts of pollutants from well defined (point) sources. Factories have been forced to put waste treatment facilities in place that recapture the polluting chemicals before they can be returned to a water body. And cities and towns have been forced to install sewage treatment systems to reduce the amounts of pollutants released from domestic sewage. Much less work has been done to reduce chemical pollutants that enter the water as part of the general runoff (nonpoint sources).

Emphasis is just beginning to be placed on reducing the sediments that enter the waters. Many major sources of sediments are still poorly controlled. Emphasis on providing tree cover along stream banks to shade the waters and prevent their warming is also just beginning. Most of the progress so far has come from the efforts of a few government agencies and from voluntary efforts by landowners.

Overfishing has been dealt with in two ways. First, government agencies in charge have set up a "fishing license" system which limits the number of fish the angler can take and for the most part prohibits commercial or market angling. This helps to reduce the pressure on the Brook Trout population. However, even with this the large number of people fishing removes fish from the popualtion faster than reproduction can replace them. A second practice is also needed:

Both state and federal agencies produce fish for anglers in hatcheries. Breed fish are stripped of their eggs or sperm, then fertilization and development occur in the controlled hatchery environment. Because there are no predators and because abundant food can be supplied many more fish can be produced than would in nature. These fish can be released into streams as fry, as parr, as juveniles, or even as adults which can be caught by anglers as soon as they are released.

The release of these domesticated trout is somewhat controversial, but it cannot be doubted that the practice allows many more anglers to successfully participate in the sport than the natural productivity of the stream could support. An additional advantage is that it allows the fish to be stocked in streams where the water quality is too poor to allow natural breeding, but where it is good enough for survival after the more sensitive hatching portion of the life cycle has passed.

Brook Trout in Legend

One story about the Brook Trout comes from the Shikellemus Indians.

References:

Carlander, K.D. 1969. Handbook of Freshwater Fisheries Biology, Volume 1. Iowa State University Press, Ames, Iowa, 752pp.

Karas, N. 1997. Brook Trout. Lyons Press, New York, 371pp.
 


 
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