Watching fish in their underwater habitat has fascinated me since early childhood. My biological research as an adult included monitoring their populations and assessing aquatic habitats.

Over the last 50 years there have been some significant changes in eastern Canada’s freshwater fisheries. The traditional, favourite freshwater fish of Maritime anglers were the Atlantic salmon (Salmo salar) and speckled trout (Salvelinus fontinalis). Recently, these cold-water fish populations have unfortunately been dealing with some serious and ongoing challenges. 

A brief natural history

Many cold-water habitats in eastern North America are warming up. That favours species that can survive in warm waters, which hold less oxygen. When water temperatures reach 20° Celsius, trout and salmon develop breathing issues. At 25°C, these fish begin to suffocate underwater. Many rivers in New Brunswick and Nova Scotia now regularly reach 30°C.

     Warming water prompts trout and salmon to seek out any remaining cold-water refuges in their waterway. Squeezed into cool spots, they become vulnerable to predators, like kingfishers and humans.  

Waterways in Prince Edward Island (PEI) tend to be cooler because many are spring-fed. Nevertheless, water tables in PEI soils are being lowered by irrigation for agriculture purposes. In addition, pesticide runoffs from fields periodically poison fish populations.

Loons are significant predators of yellow perch

Habitat changes

Many habitats for salmon and trout in rivers and streams along the Atlantic coast of Nova Scotia were eliminated by acid rain decades ago. Unfortunately, the soils that could improve acidic levels in those waterways have not recovered in recent times. Liming has helped some waterways, but it’s costly.

Historically, over the summer, many lakes developed a deeper, well-oxygenated cool water layer used by cold water fish underneath a warm upper surface layer. In more recent times, excessive runoffs of nutrients and chemicals from clear-cuts, agricultural activities, improper septic fields, and other developments have settled into those deep-water layers. The chemicals often take up the oxygen in the cool water layer, rendering the zone uninhabitable for trout or salmon. Excessive amounts of nutrients also cause an overabundance of algal and plant blooms.

Nova Scotia is a peninsula narrowly connected to the North American continent, dotted with shallow lakes and short rivers to the sea. In earlier times, marginal trout habitats were productive because they were enhanced by a sea-run component and had less competition because fewer freshwater fish species managed to migrate there in the 12,000 years since the last ice age.

Each watershed receives nutrients from its surrounding forests. That process feeds and maintains aquatic food chains. An individual lake is able to support a limited mass of fish. Put another way, lakes are somewhat like a bus, each with capacity limits, and removing their forests reduces their capacities for fish populations.

In recent decades, four-wheel drives, ATVs and new forestry roads into the last road-free areas have increased access and fishing pressure. Centuries of trout and salmon angling, where untapped yellow perch and white perch populations reside in the same waterway, now have reduced trout/salmon populations. Empty living spaces created by successful trout angling seasons open up new breeding opportunities for white perch, yellow perch and white sucker populations. The three species tolerate warmer water and can out-feed and out-breed the remaining speckled trout.

     Yellow perch have a major natural predator, loons. When pursued, yellow perch swim in an evasive, zig-zag manner that loons have mastered. A pair of loons raising two chicks on a lake can consume an estimated 1,000 pounds (454 kg) of fish over a six-month period!

     Sadly, acid rain and human activities during their breeding season have decimated many loon populations. If you live on a lake with loons, you can help. See Saltscapes 2002, Volume 3, Number 3, “Loons: The cry of a changing wilderness”.

In summary, many lakes that once hosted healthy trout populations, augmented by sea-run fish, evolved into warmer water lakes populated mostly by white and/or yellow perch, with a small, remaining trout population. Historically, populations of European brown trout and western rainbow trout have been introduced to the Maritimes. Some populations have become well-established and are spreading where habitat conditions remain favorable.

Then began the mostly illegal, irreversible introductions of warm-water, fish-eating fish.  

Introduced nuisance fish: bass and chain pickerel

Decades ago, television fishing shows featuring largemouth bass (Micropterus salmoides) and smallmouth bass (Micropterus dolomieui) caught the attention of many East Coast anglers. These big fish looked like fun, and releasing them alive became fashionable. 

Bass boats are equipped with tanks that keep fish alive. Transporting fish by trailer to another lake and releasing them became easy, but illegal. With former favourite trout lakes now full of perch, some anglers requested smallmouth bass introductions. Nova Scotia introduced smallmouth on an experimental basis. An eastward wave of illegal introductions erupted. Bass readily eat perch, young trout and salmon, endangered Atlantic whitefish, and frogs, salamanders, ducklings and other aquatic species not previously exposed to this kind of aquatic predator. 

The Miramichi River, renowned for its Atlantic salmon fishery, currently has a spreading, illegal introduction of smallmouth bass in its Miramichi Lake area. Government-backed efforts to use a pesticide called rotenone to eradicate all gill-breathing aquatic creatures in that part of the watershed are being strongly opposed. This spraying was supposed to happen in mid September. If it does, the bass kill will be incomplete, and collateral ecological damage will be major.

     Perch-filled lakes in western NS had another illegal introduction roughly 70 years ago. The saga of chain pickerel (Esox niger) parallels the smallmouth bass story, with salmon, trout and Atlantic whitefish disappearing from fragile habitats. This fish-eater also plays Pac-man with waterfowl, reptile and amphibian populations.

Dams, climate change

New Brunswick’s Saint John River is an ecologically-diverse, freshwater jewel, akin to the Danube and Rhine rivers in Europe. It once hosted excellent trout and salmon fishing. As a Fredericton teenager on the riverbank in the 1960s, I frequently watched scores of salmon jumping on quiet evenings. Then the Mactaquac dam, constructed above Fredericton, cut off the annual upriver migration of many species to spawn. Lakes behind dams have more exposed surface area to hot air. Summer water temperatures in the lower river now soar to 30° C. The environmental nature of the river gradually shifted from favouring cold water fish to warm water fish species. Voracious bass, including striped bass (Roccus saxatilis) are unfortunately faring all too well.

Muskellunge (Esox masquinongy), a larger cousin of the chain pickerel, were introduced many years ago into a Quebec lake that drains into the Saint John River. These fish-eating fish have become established in the entire river. Decades ago, a 42-pound female was netted by fisheries biologist Peter Cronin in the Jemseg River. “Muskies” join a list of exotic animal and plant species that have become established. Chinese mystery snails were sold in Fredericton pet stores in the 1960s. Now these snails are in the river, too.

PEI has no known illegal introductions of bass or pickerel but does have goldfish and koi issues. The island’s Winter River, for example, has an out-of-control goldfish population. Gradually losing their glitter over generations, goldfish become carp, and can grow to 70 pounds (32 kg) or more.

Relentless forest extraction is exacerbating the effects of climate change in all of Eastern Canada, by heating and drying up eastern waterways. Many forest-based nutrients that once sustained aquatic food chains are also being removed with the woodpiles or being flushed downstream from clear-cuts, following heavy rains. 

To maintain healthy freshwater fisheries, all three provincial governments need to focus on ecological watershed/land management as one unit. That would slow and eventually stop the degradation of forests and the aquatic habitats that support eastern freshwater fisheries.