Hunting during the dark hours, brown trout stop, listen, then attack their prey

UNLOADING LUMBER from the truck on a sunny, hot afternoon last August, I heard an uncommon commotion in the pond below the house. Speckled trout were rising quietly for insects under the cover of overhanging sumac trees, but something or things were noisily prowling the lily pads along the western shore.

The work could wait. I opted to cast a fly instead. On the fifth cast the line stopped. A tussle followed that eventually resulted in a 16-inch (40 cm) long sea-run brown trout on the dining table. Bless her frog-chasing heart, she tasted every bit as good as salmon.

Native throughout Europe and western Asia, and first introduced to Newfoundland in 1884, this particular Nova Scotian brown trout came from German and Loch Leven (Scottish) ancestral stock imported in 1923. As naturalized citizens, brown trout now inhabit some watersheds in three of the Atlantic provinces, the exception, thus far, being PEI. This may change. Their sea-run lifestyle has some populations of browns expanding along our coastlines—it’s probably only a matter of time before browns are unfortunately counted in the annual PEI fish kills caused by agricultural chemical runoff into its rivers.

Brown trout (Salmo trutta) are currently found in much of North America, from Finland south to North Africa, west to Iceland and east to Afghanistan.

They are named for the brown or golden-brown hue along their bodies. Beauties to behold, their backs and sides are adorned with dark spots sometimes circled by pale halos and with rusty-red spots. A small fatty fin on its back, ahead of the tail, has a reddish hue not found on other trout. Sea-run specimens are more silvery, with less visible spotting. Brown trout share the same genus with Atlantic salmon (Salmo salar). As populations of Atlantic salmon in the Maritime provinces decline, brown trout numbers may increase.

Brown trout prefer cool, clear rivers and lakes with temperatures of 12 to 19°C. They are able to withstand slightly higher water temperatures than native speckled trout, an advantage in the recent hot summers. More wary and elusive than other trout species, brown trout often spend daylight hours hiding in undercut banks, under rocks, beneath overhanging vegetation or among tree debris washed into pools. They also find cover under the ripples of surface water turbulence, in deep pools and will occupy large, downstream sections of river that are rarely frequented by native trout.

Daytime anglers using standard speckled trout fishing techniques may not realize that brown trout exist in a river. While working as a fisheries biologist, I once received a letter from concerned anglers about the lack of fish in a remote Nova Scotia lake. That particular watershed was home to sea-run brown trout that had become dominant in the lake. Speckled trout retreated to streams flowing into the lake to avoid being eaten by the larger brown trout.

It’s refreshing when a fish species does not behave as outdoor writers or biologists predict. The August brown trout surprised me for several reasons. It was a new species for the pond, and the harbour where I live. This female, who would have been three to five years old, swam up the small stream from the estuary, through a salt marsh, and holed up in the pond. She avoided the great blue herons, otters, mink, and mergansers that arrive there regularly to fish. And she was chasing frogs at mid-day.

A brown trout often hunts at twilight and throughout the night, even in darkness with no moon. It will cruise along slowly, listening. When it senses something moving, the fish stops, tensing its body so it makes no pressure waves underwater. Then it waits. The potential food object moves along, creating its own pressure waves and noises in the water. Brown trout use their internal ears and lateral lines (water pressure sensors along the sides of their bodies) to determine the direction the object is headed, then swim toward it. At a distance of about two feet (60 cm) from the prey, a brown trout sees it for the first time on a dark night and quickly attacks. Rather than swallow something unknown, it strikes repeatedly with closed jaw blows to stun it. At this point injured prey would begin to emit vibrations, a panic odour and the smell of blood. This enables the trout to identify it. If this fails to happen, something is wrong!

If the object is an angler’s fly, the brown trout will detect an unnatural odour and body. It may follow the fly, smelling its wake for a short distance, then reject it, turning away. After listening with inner ears, and interpreting the pressure waves with its lateral lines to intercept possible prey, a brown trout uses its senses of sight, smell and touch to strike, but not necessarily consume, potential prey.

Besides frogs, the pond’s minnows, young trout, worms, leeches, insects, and salamanders would be on an adult brown trout menu. A swimming mouse could meet a quick end. Indeed, the northern water shrews run the 10-foot (3 m) distance between an island here and the shore over the water’s surface to avoid predators.

Adult brown trout sometimes find and stay in the same watery lair year after year. During each breeding season, October to February, they begin to move upstream. Females find a spawning site that is either spring-fed, at the head of a riffle (shallow, fast-moving water) or located at the lower end of a pool. There she excavates a nest (redd) using her body to make a depression in clean gravel.

Her eggs are laid, then fertilized by a male in the redd. She covers them in gravel before the adults return downstream. Water flowing through the stones supplies oxygen to the fertilized eggs over the winter as they develop. Hatching occurs in the spring. When yolk-sacs are absorbed and water temperatures rise to 7 to 12° C, the fry emerge from the gravel and begin to hunt for aquatic insects.

Young brown trout are aggressive and soon establish territories in quiet pools or shallow, slow flowing waters where older trout are absent. They can grow rapidly, reaching sizes of 6.5 inches (16.5 cm) in their first year.

After spending two or three years in the stream of their birth, brown trout move downstream to a lake, main river or harbour. Some turn silver and migrate out to sea, where they grow quickly. These adults return to rivers and streams to spawn. Brown trout live for up to 14 years, much longer than speckled trout. For several years I operated a fish fence in a local river in eastern Nova Scotia during the period from spring ice-out to winter freeze-up. All fish traveling upriver were guided into one pen, the downriver movers into another. Some were tagged and then released. One brown trout returned three years in a row. The last time it weighed 13 pounds (6 kg).

I plan to store my assembled fly rod in the barn during angling season. Who knows what spring will bring!