Fisheries battle dip in kokanee salmon
The building blocks of Colorado’s most popular lake fisheries are no larger than an eraser on a pencil and much more fragile.
Whether you’re one of the thousands of boaters spinning circles all summer around Blue Mesa Reservoir in search of kokanee salmon or one of the fewer but no less intense hunters of trophy lake trout at Blue Mesa and Granby Reservoir, your pursuit would be much-less promising without the millions of kokanee eggs gathered each fall at a handful of Colorado reservoirs.
In recent years, for a variety of reasons and not all of them obvious, the harvest of kokanee eggs from reservoirs around the state has dipped, particularly from the reservoirs mentioned above, which historically have been the leaders in kokanee egg production.
According to Colorado Parks and Wildlife, the recently concluded harvest of kokanee eggs finished on a mixed note, with Granby and Blue Mesa well below their usual production but offset by unexpected production from Wolford Mountain Reservoir and Lake Nighthorse, part of the Animas-La Plata Project near Durango.
Parks and Wildlife fisheries biologist Jon Ewert said Granby, which at one time was producing close to 16 million salmon eggs per year, this year yielded only 72,000 eggs, not even enough to replenish that reservoir’s waters with young kokanee salmon.
And across the state, fisheries biologist Dan Brauch in Gunnison said Blue Mesa production was about 2.8 million eggs, well short of the 4.2 million eggs needed for the state’s top kokanee fishery.
However, and a big sigh here, is that Wolford Mountain, an off-channel impoundment built in 1995 on Muddy Creek near Granby, produced 1.78 million eggs, “almost 18 times the number of eggs that we need to restock it,” Ewert said. “As a result, we will use the excess eggs from Wolford to shore-up Lake Granby’s kokanee population.”
And down south, fisheries biologist Jim White was squeezing 4.5 million or so eggs from salmon trapped at Lake Nighthorse, the first year that lake has produced eggs for the state’s hatcheries.
Some of those eggs will go to Blue Mesa with the rest staying in Lake Nighthorse and others spread to other reservoirs.
The question biologists are trying to answer is why the sudden downturn in kokanee egg production in those once-prolific reservoirs?
Kokanee salmon, because of their high caloric content, are the preferred target of lake trout, and recent drop-offs in salmon numbers at Granby has resulted in a companion decline of the reservoir’s lake trout fishery.
As Brauch and the other biologists noted, fluctuation in the egg take is normal as salmon populations themselves fluctuate year to year.
Factors limiting kokanee populations include: Predation by lake trout, exacerbated by low water levels that push the predator/prey base closer together; competition from mysis shrimp for zooplankton, the building block of any fishery and especially important to young salmon; and disease in the form of gill lice.
Parks and Wildlife has made a concerted effort to reduce lake trout populations in Blue Mesa, which is managed (read: stocked heavily) to produce a reliable kokanee salmon fishery for a demanding angling constituency.
Granby, conversely, is stocked with kokanee primarily to feed its lake trout, again in response to what anglers are saying they want.
“We use kokanee as prey base to raise trophy lake trout,” said Ewert, adding the people coming to Granby for kokanee salmon virtually have disappeared.
“We don’t have the recreational kokanee angler any more,” he said. “If people are serious about looking for kokanee in the summer, they go elsewhere.”
Ewert said recent years of high water in Granby have created “ideal conditions” for plankton-eating mysis shrimp as the reservoir’s high number of lake trout chomps away at the other end of the kokanee population.
Blue Mesa went through two years of low water levels, which not only crowded fish together, but also raised water temperatures, and in 2013 an algae bloom depleted oxygen in Cebolla and Sapinero basins, which further crowded fish together.
Brauch said sonar surveys during the past summer indicated “the number of kokanee available for fishing this year and the fish available for entering the run to get eggs would be down.”
A few years ago, the kokanee population was estimated to be about 290,000 fish, but this year it topped at approximately 162,000, he said.
In recent years, biologist have increased the stocking at Blue Mesa to help offset the loss to hungry lake trout.
“We used to stock 1.4 million (kokanee) in the late 1990s, and now we’re at 3.5 million fish,” he said. “That also increased our demand for kokanee eggs.”