- Associated Press - Friday, August 12, 2016

PIERRE, S.D. (AP) - Waves crashed over the bow as two men pulled hard on a net submerged in the lake that was working hard to throw them off their wide, flat-bottomed boat.

The two guys hauled the net in as quickly as possible, it was their second of the day. Both had been thoroughly soaked by 2-3-foot waves rolling across the wide Missouri River reservoir. Spray was collecting in the boat’s flat bottom and mixing with mucus from an assortment of walleye, bass, catfish and carp that had been snared in first net the pair had hauled in.

This net came up slowly. It had gotten wrapped around a tree 30 feet down. The tree probably hadn’t seen the light of day since Lake Oahe was filled in the 1960s and came up, root bundle and all, with the net.

South Dakota Game, Fish and Parks Department Fisheries Biologist Mike Greiner worked furiously to disentangle the tree, trying not to make any holes in the net worse while bouncing from wave to wave. Greiner and his partner, fisheries intern Hunter Peterson, were part of a team of seven GFP staff working on the Peoria Flats portion of the department’s annual adult fish survey on Lake Oahe on Wednesday.

The survey is used to gather information on the health and abundance of adult gamefish in the lake that stretches about 230 miles from Pierre to Bismarck, North Dakota, said Bob Hanten, another fisheries biologist on the survey.

“It gives us an index of trends in the populations and it gives us an index of how fast our fish are growing,” he told the Capital Journal (https://bit.ly/2aOfQgP ).

The nets are 350 feet long, have seven panels of different mesh sizes to catch various sizes of fish and were set at depths ranging between zero and 60 feet. They’d been set Tuesday afternoon and were left to do their work overnight.

Wednesday morning turned out to be a bit windy, but just as biologists have done for about 50 years, the team climbed into a pair of boats to pick up the nets. They’d decided not to pull fish from the nets on the water as they usually do because of the wind.

“In South Dakota, It’s the longest-running fish survey,” said Kyle Potter, a fisheries biologists helping with the survey.

The Lake Oahe survey started with U.S. Fish and Wildlife service biologists and the U.S. Army Corps of Engineers in the 1960s, Potter said. It has been conducted roughly the same way in roughly the same places ever since.

The survey uses gill nets. Gill nets tend to kill the fish that get caught in them. But that’s ok in this case because, for the walleyes anyway, biologists need to collect a set of ear bones called otoliths from them. Those bones are used to estimate the age of each walleye caught. That’s done by counting growth rings.

All the fish caught are weighed and measured for length. That information then goes into a database that’s used to identify long-term trends in adult fish, Hanten said.

It isn’t easy work. A total of nine locations on Lake Oahe are sampled with the nets in the span of about one week. Peoria Flats was this crew’s third set of nets for the week. They had two more to do before the weekend. Another crew from Mobridge was working on four sets on the north end of the lake.

The schedule lends itself to long days, especially when the weather doesn’t cooperate. The biologists don’t generally get to choose when not to collect their nets, either.

“I don’t think we’ve missed a day in seven years,” Potter said.

The scientists are rewarded for their hard work. There’s a lot of valuable information gathered from each survey. With the walleye otoliths, biologists can get a good idea of how fast the lake’s walleye are growing each year. They also can get an idea for how many fish are in the lake and how healthy those fish are.

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Information from: Pierre Capital Journal, https://www.capjournal.com

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