Flathead Bull Trout holding their own, biologists say

Bull trout populations in Flathead Lake and the three forks of the Flathead River system are stable, Montana Fish, Wildlife and Parks biologists are saying.

The trout aren’t doing as well in other drainages of the state, however. Locally, the native trout aren’t faring as well in the Swan Lake drainage, where non-native lake trout are having an impact.

But the Flathead is holding its own.

“When we look at the overall population in Flathead Lake, it’s pretty stable,” noted FWP biologist Kenny Breidinger in a recent interview.

Lake trout have always been the main nemesis of bull trout. Lake trout out-compete native bull trout for habitat and have reproductive advantage in that they spawn in lakes, while bull trout will swim for miles into headwaters streams to spawn and then return to the lake.

One particularly bright sign in the North Fork population was last year 28 redds were counted in Coal Creek.

Biologist count redds in select streams each year as a way to gauge bull trout populations. A redd is a bull trout spawning site. The fish use their tails to excavate gravel, making a depression in the stream bed where fish lay their eggs in the gravel.

The resulting depressions, as long as the water is clear, are easy to spot.

The high numbers in Coal Creek could mark a stream on the mend, as in past years it often had just a few redds and sometimes, none, during counts.

Biologists don’t just count redds, however. They also do surveys in the lake and survey streams for young bull trout as well.

To be sure, bull trout numbers aren’t what they used to be in the Flathead. Before lake trout took over the Flathead Lake ecosystem, bull trout were far more numerous and the Hungry Horse News archives are filled with photos of large fish being caught in both the lakes and rivers.

After an initial decline, however, bull trout have stabilized, albeit at lower populations. It is illegal to intentionally fish for bull trout in the Flathead, with one exception — the South Fork of the Flathead above the Hungry Horse Dam and in the Hungry Horse Reservoir itself.

In the reservoir, anglers can keep two trout per season, with only one in possession. Anglers must obtain a free catch card and record the data as required on the card.

In the South Fork of the Flathead proper, it’s catch and release only, with a season that ends on July 31.

The idea there is to keep anglers from pursuing spawning fish.

Folks who are photographing fish are urged to have their camera ready and to release the fish as soon as possible. A fish that’s handled for even one or two minutes has a 33% greater chance of dying. The best thing to do is handle fish with wet hands are barely lift from water, if at all.

Barbless hooks make it easier to release fish.

Fish catch and release rates are good, noted FWP biologist Leo Rosenthal, ranging from 350 to as many as 700 annually.

Anglers release most of the fish, even when they can keep them in the reservoir, Rosenthal noted. The annual take is about 40 to 50 fish annually.

The reservoir and South Fork do not have lake trout — the Hungry Horse Dam keeps them from migrating up stream.

The greater challenge is the Swan Lake drainage. FWP tried netting out the lake trout to suppress populations for nine years a few years ago, but it wasn’t effective, Rosenthal noted.

In Yellowstone National Park, they’ve started using lake trout against themselves. In an experimental procedure, pelletized lake trout carcasses were spread on known spawning sites.

Preliminary results look promising, but the effort has just begun.

Biologists didn’t have enough carcasses to treat the entire lake, so they turned to pelletized soy and wheat gluten pellets, according to a story in the Jackson Hole News and Guide.

The pellets rot on the bottom of the lake at the spawning bed, depriving it of oxygen, which, in turn, kills the lake trout embryos.

Rosenthal said FWP will wait to see final analysis of the Yellowstone work before it would consider lakes in this area for the procedure.