Merwin net plays role in corralling kokanee

Lake Nighthorse near Durango was stocked in 2010 with kokanee salmon, and this year was the first year biologists could harvest salmon eggs to replenish kokanee populations around the state. Some of the salmon trapped this year are pictured in a holding pen.



This overhead view shows how a Merwin net can funnel shore-cruising kokanee salmon into deep-water holding pens, where the fish can be spawned. The net this year allowed Parks and Wildlife to harvest 4.8 million salmon eggs from Lake Nighthorse.



A new tool in the arsenal of state fisheries biologists helped boost this year’s harvest of kokanee salmon eggs.

Biologists Jon Ewert of Hot Sulphur Springs and Jim White in Durango this year used a Merwin net to corral kokanee salmon that otherwise might have escaped the fall egg harvest.

The net, a style previously used successfully by the New Mexico Department of Game and Fish, attaches at one end to shore and then runs out a long (up to 150 yards) lead into the lake or reservoir.

This lead, basically a curtain of netting from the water surface to the bottom, then funnels fish through one-way openings into holding pens where the fish are held until spawned by biologists.

These nets are particularly effective on fish such as kokanee salmon in lakes with no or very small inlets, said Ewert, who used the net to gather 1.8 million eggs from Wolford Mountain Reservoir.

“What kokanee do when they are ready to spawn is to cruise fairly shallow (and) close to the shore, looking for places to spawn,” Ewert said.

When a fish hits the net, it funnels the fish out into the reservoir and the larger holding pens.

White used the net at Lake Nighthorse, the off-channel impoundment south of Durango.

Getting 4.5 million eggs from Lake Nighthorse was particularly gratifying, said Parks and Wildlife biologist Dan Brauch of Gunnison, who saw this year’s egg take from Blue Mesa Reservoir slump to 2.8 million eggs, not enough to replenish the reservoir.

“To bring eggs into any of our hatcheries we need a three-year (disease) history, and this was the first year we have that from Lake Nighthorse,” Brauch said. “This came at a great time to help us get the number of eggs we need statewide.”

Plus, Ewert said, the two lakes show future promise because they are among the few in the state with no predation by lake trout, no competition from mysis shrimp and no gill lice.

Brauch has used a similar technique since 2010 to fence off the East River near the Roaring Judy Fish Hatchery and stop salmon from swimming past the hatchery.

In past years, so many fish would miss the turn into the hatchery and continue upstream that Brauch and his crew would chase the fish and try to net them for spawning.

“Screening the East River has resulted in a big bump” in egg production, he said.

“Now we install the barrier in late August and early September for the entire run,” he said. “In 2012, we took 13 million eggs (from) Blue Mesa, the most we’ve ever taken there.”


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