Featured Creature: Brook Trout

What might well be considered the most beautiful freshwater fish, beloved by anglers and everyone else, especially when dressed up in its fall spawning colors?

The ‘brook trout,’ of course, or salvelinus fontinalis, which is actually a char!

Photo from On The Water

 

Where do we find this beauteous creature?

Brook trout, otherwise known as brookies, eastern brook trout, speckled trout, brook char, squaretail, or even mud trout (though I’ve never heard them called that last one), are native in the Northeastern part of North America with the greatest abundance of wild brook trout in the state of Maine. Indeed, Maine is the last true stronghold for stream dwelling populations of wild brook trout, supporting more than twice the number of intact subwatersheds as the other 16 states in the eastern Appalachian mountain range combined. 

According to fisheries biologists, there are two genetically distinct brook trout consisting of northern and southern strains, separated by the New River drainage in southwest Virginia. The southern strain is often referred to as speckled trout and is less diverse, making these brook trout populations more fragile to change and catastrophic events than the northern variety.

Brook trout have also been introduced as exotic or ‘invasive’ non-native species elsewhere in North America (find a history of these efforts here), as well as in many parts of Iceland, Europe, and Asia. A migratory population in Lake Superior is known as “coasters,” while an anadromous (sea-run) subspecies in the New England coastal rivers of Maine and Massachusetts is locally designated as “salters,” which used to range as far south as New Jersey.

The brook trout has the honor of having been named the state fish in nine U.S. states, which include Michigan, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Vermont, Virginia and West Virginia; it is also the Provincial Fish for Nova Scotia in Canada. This fish is clearly beloved by anglers everywhere!

U.S. native and introduced ranges of brook trout

What’s in a name?

Despite the ‘trout’ in its name, brook trout are actually part of the char branch of the family tree. Char, trout, and salmon are all related as part of the salmon family (salmonidae) and subfamily (salmoninae), but if you’re strict about classification, you might start to think brook trout are misnamed. 

As a char it is most closely related to lake and bull trout, Dolly Varden trout and Arctic char, but not actually to other trout. Char are distinguished from other trout and salmon species by the absence of teeth on the roof of the mouth, the presence of light colored spots on a dark colored body, their smaller scales, and differences in skeletal structure. In contrast, the true trout have light base coloration with a pattern of dark spots.

What about appearances?

The color of brook trout actually depends on the conditions of their habitat. The typical brook trout has a dark green to brown color, with a distinctive marbled pattern (called vermiculation) of lighter shades and a sprinkling of red dots, surrounded by blue halos, adding variety and beauty. The brook trout has belly and lower fins that are reddish in color with white along the edges, and have square or slightly forked tail fins.

During fall breeding time, male brook trout will develop a slightly hooked jaw and brighten up in its orange-red areas. Non-breeding adults are similar except that their pale patterning has less contrast, their red spots are pale or unapparent and their orange or red lower sides are pale to absent. Spawning season gives brook trout a good reason to dress up, breaking out their best.

Young Native Appalachian brook trout
Photo from factfile.org

Usually, full-grown brook trout vary from 10 to 26 inches with weights from 2/3 to 7 pounds, but the maximum recorded length and weight of this fish was 34 inches and 15 pounds! Brook trout can reach seven years of age, with reports of 15-year-old specimens observed in certain areas in California where they were introduced. 

Their growth rates depend on season, age, water and ambient air temperatures, and stream flow rates. For example, springtime growth rates curiously increase with temperature at a faster rate with fast flowing water than at lower stream flow rates, perhaps due to higher oxygen levels available to the fish. And across different stream-dwelling populations of brook trouts, having closed canopy forest cover is crucial to their long-term success. The more intact forested area, the better!

What do they eat, and what eats them?

Unlike other members of the salmon family, brook trout have no teeth on the roof of their mouth, but that doesn’t stop them from eating a wide array of food sources. The only apparent limitation in the diet of brook trout is likely the size of their intended prey. Their diet includes nearly any aquatic or terrestrial invertebrate or vertebrate of suitable size that either occurs naturally in the stream or happens to fall in. In turn, they are preyed upon by northern water snakes, mink, kingfishers, herons, snapping turtles and the occasional otter. 

Brook trout feed on aquatic insects of various kinds as well as small freshwater shrimp and other crustaceans, minnows and molluscs. The larger ones will also eat frogs and even swimming mice or voles. Talk about a wide diet! Brook trout are primarily twilight feeders and therefore most active near dawn and dusk. During mid-day hours, brook trout are more likely to retreat to deeper waters or shaded areas if available to provide some overhead security when they are not feeding. Behaviorally, brook trout are aggressive predators but are cautious and easily spooked.

Photo from Bangor Daily News

How do brook trout reproduce?

Brook trout normally mature in two years but may spawn after one year. Spawning is generally triggered by decreasing day length and water temperature, usually between September and October. Pre-spawning starts with the male brook trout attempting to drive a female brook trout towards the spawning area. Females dig out shallow redds (depressions in gravel streambeds) into which they deposit their eggs. The eggs are then fertilized by any males that can push their way into the game. While the female brook trout is digging, the male brook trout continue their courtship activity, darting alongside the female and quivering, swimming over and under her and rubbing the female with their fins. Each male fish also spends a great deal of time and effort driving off other males during this process.

After spawning the female covers the eggs (up to 5,000 per female) with gravel. Brook trout eggs must stay silt free and get continuous amounts of oxygen rich water in order for the eggs to survive. So the female uses her body and tail to disturb enough upstream gravel to carefully cover the redd or nest to protect it from egg-consuming predators, of which there are many eager takers. After hatching and developing in their gravelly nests, they emerge sometime between February and April.

Young-of-the-year brook trout normally seek shelter in submerged aquatic vegetation or shallow water near the shoreline after they hatch, to avoid their many predators, which includes larger brookies. If they’re not careful, they could even be eaten by their own parents!

Dealing with human impacts

Brook trout have a low tolerance for pollution, temperature increases and acidity. They can thus be used as a test – like canaries in a coal mine – for healthy aquatic conditions. They prefer clear waters of high purity and a narrow range of acidity (pH) and are sensitive to poor oxygenation, pollution, and changes in pH caused by environmental effects such as acid rain. Water temperatures in their habitats can typically range from 34 to 72 °F, but this means that warm summer temperatures and low flow rates with poor oxygenation are extremely stressful for brook trout populations, and most especially for the larger specimens.  

Within their native range, brook trout have been observed making upstream movements in early spring, summer and late fall, and downstream movements in late spring and early fall. This is one of the reasons that dams have been so destructive to trout habitats, both in preventing their movement to the refuge of cold water during warm summer months, but also because still water trapped behind dams accumulates a lot more heat than when these rivers are allowed to flow freely, undammed. 

Flood and drought events are likely the leading causes of sudden and dynamic change within brook trout populations. Additional external stressors such as over-harvesting, the presence of a non-native predatory fish population, disease outbreaks and changes in water chemistry due to acidification could result in the loss of a brook trout population from local streams over time. 

Brook trout have been the beneficiaries of a large-scale restoration partnership known as the Eastern Brook Trout Joint Venture supported by Trout Unlimited and many other fisheries conservation agencies. For example, stream restoration efforts have included riparian forest buffer plantings and the insertion of woody debris, both of which have improved water quality and cooled stream temperatures benefitting wild trout found in these waters. A riparian buffer is a zone of trees and vegetation between water and an open, upland area. They shade the water, stabilize banks, and intercept surface runoff. Studies show that water temperature is 10 degrees cooler in streams that are lined with buffers, which can make all the difference in brook trout survival. The insertion of woody debris helps to provide brook trout with safe niches to hide and thereby protect themselves from predators. 

Red Brook restoration – placing woody debris into trout habitat (Photos: Warren Winders)

There is a very good reason that conservation organizations such as Trout Unlimited focus on the restoration, protection and preservation of cold-water fisheries. These are ways to maintain and enhance angling and other recreational opportunities, and to cultivate the development of healthy riverine ecosystems. That’s why I became a Lifetime Member of this great organization many years ago!