Biologists Trawling for Swan Lake Interlopers

By Beacon Staff

SWAN LAKE – State fishery biologists will trawl their nets through Swan Lake this summer, snagging invasive lake trout in a continuing effort to reduce the numbers of non-native fish.

The plan involves gill netting fish during a three-week period from late August into September. Biologists with the Montana Department of Fish, Wildlife and Parks hope information gathered from the catch will help them better understand the characteristics of Swan Lake’s lake trout population — numbers, ages, genders and other data.

Armed with that information, they say they can better target the fish and devise procedures to drive down the non-native population.

A similar netting program last summer hinted at a far larger lake trout population than anyone anticipated, and unfortunately, those fish like to eat. High on their menu are native fish, such as bull trout, treasured by anglers and protected by law.

The upcoming netting operation, officials said, could help researchers understand how the lake trout invasion is affecting the native fishery.

Most revealing from last season’s netting was the discovery of a very large population of young lake trout on the cusp of reproductive maturity. When those fish finally grow large enough to really eat and spawn, researchers said, the resident kokanee salmon and bull trout will be hard hit.

Swan Lake remains one of the few places in the nation where anglers can catch and keep bull trout, but their future in the lake has been in doubt since 1998, when the first lake trout invader was recorded in the Swan. In nearby waterways, long-running studies suggest that once lake trout colonize, they out-compete and fully replace native bull trout in about 30 years.