Confederated Salish-Kootenai Tribal officials say things have changed to a point where more needs to done, including netting of non-native lake trout, to save native bull and cutthroat trout in the Flathead Lake.

When netting was first discussed in 2006, it was prudent to be cautious and explore other means of suppressing the lake trout population, a group of tribal officials said during a press conference Monday in Polson.

Since then, much has been learned about the ecology of Flathead Lake and its connected river system, and that knowledge is now embodied in a 650-page draft environmental impact statement outlining several alternatives to further reduce lake trout numbers and begin increasing bull trout numbers, said Barry Hansen, the tribes’ lead biologist on the project.

“Despite our best efforts, we haven’t brought about an increase in native fish abundance,” Hansen said.

Most notable among those efforts has been the fall and spring Mack Days fishing events, with anglers in recent years removing more than 40,000 lake trout a year.

The catch has included tagged fish that have provided an “enormous” data sample that led to a 2010 population estimate of 1.5 million lake trout in the system, Hansen said. Bull trout, meanwhile, are estimated to number around 3,000 adult fish.

Despite Mack Days and millions of dollars spent on habitat improvements and conservation, there has been no change in the trajectory of the bull trout population, and that is what is driving the proposals for netting on Flathead Lake, Hansen said.

“The limiting factor, the driving factor holding them down, is predation by non-native fish,” Hansen said.

The environmental study offers a status quo alternative that would involve continuing Mack Days events and the general fishing season, which produce an annual estimated harvest of about 70,000 fish.

However, Hansen said Mack Days are not likely to continue without netting as a complement because they have not succeeded in suppressing lake trout to the extent that would benefit bull trout.

The study includes three alternatives that would seek to reduce the adult lake trout population by 25 percent, 50 percent or 75 percent over  a period of 50 years or more.

Those alternatives would involve removing 84,000, 112,000 or 143,000 lake trout annually by deploying increasing lengths of gill or trap nets. Those numbers all include the 70,000 fish harvested by anglers annually.

“We think this is a very modest proposal” that will not lead to total restoration of bull trout or total eradication of lake trout, Hansen said.

Any proposal to gill-net on Flathead Lake is bound to encounter opposition, however. Montana Fish, Wildlife and Parks, for starters, already has sounded off with its concerns.

In an official position statement, the agency characterizes gill netting as an “aggressive” measure that is not necessary because the bull trout population is 60 percent above a “secure” level, as defined in an expired co-management plan that was in place between the tribes and the state for most of the last decade.

The position statement also asserts that there is “a high level of uncertainty” with population modeling. “We believe that the analysis underestimates the risk to bull trout from gill netting actions and overestimates the benefit to bull trout,” it states.

State officials are “very concerned” about bull trout mortality from gill netting, also referred to as “by-catch.”

“Of course, by-catch is a big issue,” Hansen acknowledged. It can be mitigated by timing and location of netting efforts, the net mesh size and using adaptive approaches to netting.

According to the environmental study, a by-catch of 221 bull trout annually is predicted under the first netting alternative, 338 bull trout for the second and 467 bull trout for the third.

Hansen said by-catch would be monitored closely and if it was deemed excessive, “we would have to suspend netting.”

Lake whitefish also are predicted to be impacted. The environmental study states by-catch would be 35,000, 105,000 or 182,000 whitefish under the respective alternatives.

Critics frequently say that gill netting will have a detrimental impact on all fishing, particularly with lake trout, the prominent sport fish on the lake. “We also believe that the impacts to the recreational fishery are underestimated” by the tribes, the Montana Fish, Wildlife and Parks position statement says.

Tom McDonald, the tribes’ fish and wildlife division manager, contends that there will be recreational and economic impacts if nothing more is done to suppress lake trout. If bull trout, currently listed as a threatened species, are classified as endangered, there could be substantial costs.

“It’s simply not enough” to continue with the status quo, he said. “The evidence suggests [bull trout] are not increasing.”

McDonald said that for years state and tribal fisheries managers have been taking a risk in hoping that the bull trout population would persist.

At any time, there has been the potential for an unpredictable “cascading collapse” of the bull trout population, and now tribal officials want to do more to reduce that risk, he said.

The study can be viewed and public comments can be submitted through Aug. 5 online at: www.mackdays.com.

Reporter Jim Mann may be reached at 758-4407 or by email at jmann@dailyinterlake.com.