GF&P surveys Lake Thompson
Wednesday, August 12, 2015
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Bruce Johnson, a research biologist with the South Dakota Department of Game Fish & Parks, and three GF&P interns conducted a survey last week at Lake Thompson.
The crew put out four overnight gill nets and 10 trap nets on Aug. 3-4 and retrieved them the following days. They use GPS coordinates to place nets in the same locations each year so they can easily find them and accurately compare data from year to year.
Gill nets, which are placed offshore, are 150 feet long. Johnson said the nets have six sections with different sizes of mesh. Each section is 25 feet long. The different sizes are designed to capture different sizes and species of fish.
Fish trapped in the gill nets do not survive, but the dead fish are not wasted. Data collected includes numbers, weights, lengths and species. The GF&P also determines the age of some fish by removing the inner ear bones, also known as otoliths, from a sampling of the fish caught in the gill nets. Johnson said the age of a fish can be determined in the laboratory by examining its ear bones, which form a layer of calcium carbonate every year, much the same way a tree’s age can be determined by counting the rings.
After data is documented and ear bones removed, fish remains are disposed of where other wildlife will find and eat them.
The De Smet News