Follow the Fish

Hauser and Holter reservoirs are two of the most popular fishing destinations in Montana. Combined, the two reservoirs see about 120,000 angler visits each year.

NorthWestern Energy is committed to keeping those fisheries healthy.

“These reservoirs provide an incredible amount of recreation and revenue to the state economy,” said NorthWestern Energy Biologist Grant Grisak.

Protecting fish populations and enhancing fish habitat are some of the requirements included in the Federal Energy Regulatory Commission license that directs the operations of the dams on the Missouri River.

We partner with Montana Fish, Wildlife and Parks to harvest eggs from wild rainbow trout at Holter Lake, raise the eggs into trout and stock them in Holter and Hauser reservoirs.

STEP 1: ELECTROFISHING

On an evening in April, Grant joined two FWP biologists to capture fish at Gates of the Mountains on Holter Reservoir.

The fish capture is done through electrofishing. An electrical current is sent into the water, which temporarily stuns the fish, causing them to float to the surface. The fish are scooped up with a net and kept in holding nets in the lake.

The biologists captured 300 fish over three nights, which is generally enough to meet the requirements for stocking Canyon Ferry, Holter and Hauser.

STEP 2: TROUT EGG TAKE

Once the fish are captured, a group of FWP biologists gather on the shore at Gates of the Mountains to harvest eggs from the fish.

“A typical rainbow trout has about 3,200 eggs,” Grant said.

The group collected about 400,000 rainbow trout eggs, which were mixed with sperm collected from male fish.

In addition to harvesting eggs and sperm, the weight and length of each fish is recorded and samples are collected to monitor fish health.

STEP 3: THE HATCHERY

The fertilized eggs are transferred to the Big Spring Trout Hatchery in Lewistown, Montana.

At the hatchery, the eggs are placed into an incubator where they’re monitored every few days. After 50 to 60 days, the eggs hatch and the fry swim out of the incubator and into a large trough.

After another 14 days, the fish develop mouth parts and begin eating feed.

“From that point on, they monitor their growth and health until they’re ready for planting,” Grant said.

As the fish grow, they are moved into larger troughs. Depending on how much they feed the fish, biologists can be fairly precise about how big they will be at a certain point in time.

STEP 4: FISH MARKING

By June, the fish are about 4 inches long, and at this point, they’re marked to identify their strain.

The Lewistown hatchery primarily raises two strains of rainbow trout – Arlee trout from the hatchery in Arlee, Montana, and Eagle Lake trout, a strain that originated in California.

The Arlee trout are marked by removing the fish’s adipose fin.

“It’s a non-essential fin on their back,” Grant explained. “It’s a non-lethal mark that’s noticeable to a biologist.”

When trout eggs are harvested from Holter, biologists only capture non-Arlee trout. So if they see a fish missing its adipose fin, they throw it back. That means the eggs harvested at Holter are most likely from Eagle Lake trout.

To mark the Arlee trout, fish are corralled in an outdoor raceway and then placed into small tubs, where a little anesthetic is added so the fish are easier to handle. Fish marking is a major undertaking. In all, about 230,000 fish have to be handled, and it takes upward of 30 people working most of a week to tackle the task.

STEP 5: STOCKING

In mid-September, FWP employees from the hatchery in Lewistown start hauling fish and releasing them in Holter, Hauser and Canyon Ferry. The fish are about 4 months old and 8 inches in size, big enough that they have a good likelihood of surviving in the wild.

“The smaller the fish is, the more vulnerable they are to predation by other fish,” Grant said.

They stock both Arlee and Eagle Creek trout. These two strains of rainbows are stocked in Helena-area reservoirs because they grow to a large size quickly, they survive well in these reservoirs and are easily caught by anglers.

The fish are transported from the hatchery in large, specially designed trucks that can hold about 9,000 to 11,000 8-inch fish. Oxygen is constantly flowing through the water tanks on the trucks to keep the fish healthy in transit. Once they reach the reservoirs, the fish are transferred into the lake via a long tube that attaches to the trucks’ tanks.

In all, the hatchery stocked about 400,000 rainbow trout in Holter, Hauser and Canyon Ferry reservoirs. Another 300,000 fish from other hatcheries around the state are released in the reservoirs.

THE RESULT: A THRIVING FISHERY

On odd years, Grant and his colleagues electrofish below Hauser Dam to monitor fish populations. They always find some large rainbows with missing adipose fins.

“Those are all fish that came through the Lewistown hatchery,” Grant said.

“There are massive fish down there.”

NorthWestern Energy’s involvement

The partnership of funding, equipment and staff allows both NorthWestern and Montana FWP to maintain valuable public recreation opportunities like rainbow trout angling at Hauser and Holter reservoirs.

NorthWestern Energy funds a portion the salaries for FWP staff who work throughout the fish stocking process and some operational costs. We also provide our boat, equipment and personnel to help.

We provide funding for monitoring of the fisheries at Holter and Hauser, which is done through gill netting and creel surveys. Gill netting allows biologists to monitor the fish population and provides data on fish size and species prevalence. Creel surveys are done by asking fishermen about how many fish they caught, what kind and how many hours they spent fishing.

All of this is done to maintain the healthy fisheries enjoyed by thousands of anglers every year.