Scientists study salmon stocking methods

By Mike Lynch

Scientists are taking a new approach in their Atlantic salmon stocking efforts in the Lake Champlain watershed. 

This fall a crew from the U.S. Fish and Wildlife Service began netting salmon to collect data about their journey up the Ausable, Boquet and Saranac rivers during their annual spawning run. The work is part of a new 9-year study researchers are undertaking that relies on parentage-based tagging, a novel method of tracking fish that identifies their familial roots using DNA.

“The big picture goal of the study is to evaluate different stocking practices that we can use to restore landlocked Atlantic salmon,” said biologist Kurt Heim, who is heading the federal study.

Heim said one of the main goals is to evaluate Altantic salmon with different DNA that are being stocked in rivers. One group of salmon has what he calls “maximum genetic diversity,” while the others have genes that have shown to have a high level of tolerance to low thiamine (also known as B1 vitamin) levels in their systems.

Salmon in Lake Champlain that eat a lot of alewives, a small invasive fish, have been found to develop low thiamine levels. Studies have shown that adult salmon with low thiamine levels can struggle to migrate during the fall spawning run, their eggs often fail to produce salmon or fry have lower survival rates.

Scientists are also studying how fish of varying ages adapt to being stocked. The federal hatcheries in Vermont stock salmon of different life stages, including as fry, which are fish that have recently emerged from eggs, and 1-year-old smolts.

The scientists are hoping that by better understanding stocking methods they can add fish to the Lake Champlain watershed that are more likely to reproduce successfully in the wild. 

Atlantic salmon were extirpated from the Lake Champlain watershed in the 1800s because of overfishing, dams and pollution. In recent decades, state and federal agencies have made efforts to restore their population. A program to control salmon-sucking sea lamprey was put in place, a dam in Willsboro was removed, and studies have been undertaken to understand the fish. 

Collecting fish and DNA

On an average weekday in late September and throughout October, Heim’s crew, which is based in Essex Junction, Vt., ferried across Lake Champlain to visit the New York rivers to study salmon. 

Weather permitting, they set up nets on Mondays on the three rivers, and then checked them for fish the next four days. The nets were removed on Fridays for the weekend. 

The net crossed the entire river and guided fish toward the center where they were captured. When there were fish in the net, the crew took the gear to shore, where they used a handheld net to scoop the fish and put them in plastic bins filled with water. 

From the shore, crew members weighed and measured the fish and took a DNA sample from one of the fins. The fish was then released. 

In addition to using overnight nets, which they have stopped doing for the season, the crews have also been using another technique. The method relies on them putting a net in a pool for less than a minute before it is retrieved. They finish up that netting procedure this week. 

Either way, once a fish is caught and a DNA sample taken that info is added to the U.S. Fish and Wildlife’s database. If a fish they catch has been stocked for this particular study, they will find its parents’ DNA in their database. A salmon lays thousands of eggs.

The first young fish for the project were stocked in New York rivers this past spring.

“We’re going to know from this study how effective fry stocking is at producing adult Atlantic salmon that return to rivers,” Heim said. “It’s really about learning which techniques in our toolbox are working the best.”