The South Fork a bastion for bull trout, anglers

They can grow to more than three feet long, weigh up to 20 pounds and live for 10 years. For many anglers, they’re the light-tackle thrill of a lifetime.

They’re bull trout, the grizzly bear of the underwater world, gobbling up native whitefish and cutthroat trout in a single gulp with their enormous mouths.

For all their underwater prowess, bull trout are a vulnerable fish. They need cold, clean, water and they don’t do well when faced with competition from non-native predators like lake trout.

In areas where non-native lake trout have been introduced, the native bull trout are struggling to survive.

The South Fork of the Flathead above the Hungry Horse Reservoir is one of the last bastions for the iconic fish, noted Montana Fish, Wildlife and Parks fishery biologists Mark Deleray and Leo Rosenthal. A member of the char family, they were once called Dolly Varden, named after a dress pattern from the 1800s. Char differ from trout in that they have light colored spots over a darker body, while a trout has black spots on a lighter body.

In 1978, the name was changed to bull trout, Deleray noted. Another closely related fish is still called Dolly Varden, but runs up rivers in Alaska from the ocean, while the bull trout is a freshwater-only fish.

The Hungry Horse Dam has provided a refuge of sorts for the South Fork bull trout population. The dam keeps non-native lake trout out of the ecosystem and the river system largely drains unmolested wilderness waterways, rife with the cold water upwellings that bull trout need to spawn.

The fish are fluvial, meaning they generally grow to adults in lakes and spawn in the smaller rivers and streams. The Big Salmon Lake bull trout fishery in the heart of the Bob Marshall Wilderness is completely separated from the south Fork and is genetically distinct. They fish will spend two to four years as juveniles in streams and rivers, grow to adults for several years in lakes and then return to the same rivers and streams where they hatched to spawn again.

The South Fork is one of the few places in the U.S. where anglers can still legally fish for bull trout. Bull trout were listed as threatened under the Endangered Species Act in 1998, but in 2004, under an agreement with the U.S. Fish and Wildlife Service, FWP started a program to allow limited fishing for bull trout in the Hungry Horse Reservoir and South Fork of the Flathead.

In the reservoir an angler can keep two fish per year and have to keep a “catch card” record of the fish they catch. Using data from the catch cards, Rosenthal said 80 to 90 percent of the fish caught in the reservoir are released.

On an annual basis, about 250 to 400 fish are caught and released each year in the South Fork and 600 to 800 in the reservoir.

FWP biologists keep close tabs on the health of the fishery. They routinely count redds in certain tributaries every year and in some years, they do basinwide counts. Redds are spawning beds in the gravel. The female excavates a large gravel bed and lays her eggs in it. By counting the redds, biologists can get a good idea of the health of the population.

The South Fork fishery continues to remain robust. Youngs Creek, which is the headwaters of the South Fork, routinely has counts of 70 to 80 redds, the White River, 65 redds, Big Salmon, 84 redds. But bull trout can be fickle. Danaher Creek, which forms the other half of the South Fork headwaters, usually has less than 10 redds.

The redd data over the years in the South Fork has seen ups and downs, but averaged over time has been flat, Rosenthal said.

“Which is good news,” he said. It means the population is stable, even with angling.

Counting redds is tough work, Rosenthal noted. Just to count the redds in the White River, it takes two biologists, a pair of horses and an entire day. The horse travel is about 14 miles and the foot travel is an additional 10 to 12 miles, off trail and through streams littered with downfall.

“We get done about dark,” Rosenthal said.

There are some concerns about the South Fork fish, climate change could warm the waters, making them unsuitable for the fish. But based on data being compiled by a doctorate student, that doesn’t appear to be the case, yet.

The geography of the Bob may prove to be a buffer for bulls. In addition, the use of lightweight packrafts is causing an increase in use of the river. So far the added angler pressure doesn’t appear to be having an impact on the fish, but FWP is keeping tabs on it.

Rosenthal urged anglers to treat any bull trout they catch in the river gently. If possible, don’t even lift them from the water when taking a picture.

“These are delicate fish,” he said.