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Trout management relies heavily on stream surveys (06/06/2004)
Electricity is a marvelous thing. Flip on a light switch and a room is instantly lit.

Electricity is also valuable in ways many of us probably don't realize. As an example, for capturing fish. Fishing with electricity is "the most valuable tool we have for monitoring fish populations," said Eric Merten, Department of Natural Resources (DNR) natural resources specialist at the Lake City DNR Fisheries office.

Called electro-fishing, the DNR depends on this technique to evaluate fish populations, streams and rivers in southeast Minnesota. Trained biologists use high-tech equipment to direct electrical currents into the water to temporarily stun fish. When the fish rise to the surface, they are quickly netted, counted, measured and released. "The relative abundance of different fish species indicates the suitability of the stream for trout," Merten said. Trends in trout abundance over time may also indicate what's happening in the watershed, in terms of stream flows and water quality.

Scale samples are also taken from a sample of trout. This information is used to estimate trout age, growth rate and mortality rates.

Electro-fishing, Merten noted, is a primary strand in a web of survey and evaluation tools the DNR employs to obtain the data and knowledge necessary for effective fisheries management. About 20 percent of DNR Fisheries efforts in the southeast are spent on surveys and evaluations.

"Information collected focuses primarily on game fish, however we are increasing our efforts to understand fish communities, and how they are affected by habitat, water quality and land use. This information is vital to remove the guess work in fisheries management."

Trout habitat that includes deep pools, wood, or large rocks are also evaluated to help determine a stream's carrying capacity. Stream channel dimensions are surveyed to ascertain whether it's "in sync with water and sediment inputs from the watershed," Merten said. Streams that are out of sync (unstable) tend to have poorer trout habitat and high rates of bank erosion.

To measure stream temperature and water quality, fisheries biologists routinely use in-stream monitoring devices or thermal imagery technology. "Stream temperatures and water quality are critical to trout abundance and it's very important that we keep close tabs on those conditions," Merten pointed out.

Merten said the DNR also uses information collected from anglers interviewed on the stream (creel surveys), as well as with mail and phone surveys. Creel clerks visit with anglers to document the type of gear being used, how many and what sizes of fish they are catching, which fish they choose to keep, and fishing pressure.

Trout stream management is like a jigsaw puzzle that includes biology (fish, plants, insects), physical habitat (the stream, riparian area and watershed), and anglers" Merten stated. "If you don't have all the pieces, you can't see the whole picture. Collecting all of this information takes a lot of time, but it's absolutely necessary for effective trout management to occur. 


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