Throughout the Canines Assisting Conservation series, we have looked at how trained dogs have been on the front lines of conservation protecting imperiled species.  We have also examined how dogs are assisting with the eradication or spread prevention of noxious alien species.  However, never has our target species needed both conservation and eradication.  The brook trout (Salvelinus fontinalis) is our first species that is in the unusual position of needing support in its native habitat, while at the same time needing control in other parts of the country.  

Brook trout, otherwise known as Eastern brook or speckled trout, or simply by the nickname “brookie,” are native to the freshwaters of the Eastern United States and Canada.  Measuring between 9-25 inches on average, this medium-sized relative of salmon is a generalist consumer, eating a wide variety of insects, amphibians, smaller fish, mollusks, and other invertebrates.  Their appetite for larval, pupal, and adult insects is an important method of controlling these pest populations, so brook trout are often used as indicator species of healthy stream habitats.  Although brookies can tolerate a wider range of water conditions than most other salmonids, they are still restricted to cold, clear water free of pollution.

Soil erosion, fertilizers, and particularly acid rain all pose threats to brook trout populations.  As East coast human populations continue to thrive near rivers, pollution and temperature also increase within these waterways due to commercialization and riparian zone destruction.  Being sensitive to water clarity and temperature, brookies are being forced into the cleaner, colder streams of the higher elevations in the East.  With less and less suitable habitats available, brook trout populations have been steadily declining for decades. Many state wildlife agencies have protections in place or even recovery goals regarding imperiled eastern brookies.

Brook trout are a favorite catch of anglers, so beginning in the 1850s the fish or their eggs were intentionally transported to Western waterways where they are not native.  Well-meaning fishermen had no idea they were releasing what would become one of the West’s worst aquatic noxious species.  The invasion did not stop there, though.  Brook trout have been introduced to every continent except Antarctica due to their popularity among sportsmen.

Unfortunately, these alien invasions have caused significant detriment to native populations of fish and amphibians.  In the Western US, brook trout have outcompeted the native cutthroat and bull trout by overcrowding streams and consuming their insect prey.  Some studies have shown up to a 36% reduction in food resources for native species in streams containing the invasive brook trout.  Additionally, sixteen amphibian species have been documented as decreasing or locally extirpated directly due to this increased brook trout consumption of insects.

Due to these detrimental effects, many states have imposed control measures on invasive brook trout including unlimited bag numbers or even required kill mandates for any brookie caught.  Still, brook trout continue to expand across Western waterways causing damage wherever they go.  As with any wildlife control attempt, the most difficult hurdle is locating the species to be controlled.  Traditional methods of inventorying stream occupants are through electrofishing or setting fish traps, both of which cause harm to the native fish as well as the target noxious species.  If brook trout are found, then eradication methods include complete electrofishing of all stream occupants or spraying deadly toxins into the water.  Both methods kill all fish within the area, further reducing native populations.

A better method for locating noxious brook trout was needed.  Such a technique could also be used to assist native brook trout conservation in the Eastern US.  Creative biologists wondered if the olfactory abilities of dogs might be able to detect differing scents of separate fish species.  Conservation canines have already been incorporated into studies on whales, so living submerged in water might not be an obstacle for the dogs.  Turns out, dogs can detect the presence of brook trout adults and even eggs with great accuracy!  Former WERC biologist Megan Parker was one of the researchers who refined this olfactory detection method that is now being used across the country to find brookie locations.

With the assistance of trained dogs, conservationists can now accurately survey existing populations of brook trout among their native waterways in the East.  Once found, protections can be established for these critical habitats, promoting survival and expansion of the important aquatic predator.  Likewise, the brookie-seeking dogs can also find noxious alien populations of brook trout in Western waterways, allowing wildlife managers to contain the spread of the invader or set up elimination practices that minimize impacts upon native fish species.  The locator abilities of conservation canines have been the largest success story of both brook trout conservation as well as eradication since studies began on the species.  Our canine friends are helping make waterways healthy again across North America.