Drought impacts salmon run
Low water levels force different strategy for spawning salmon
Withered crops and steep hay prices. Underwhelmed river guides. Overworked firefighters. Neighborhood visits from hungry, foraging bears.
Drought conditions have thrown the rhythms and daily routines off kilter for many Colorado subgroups in 2012, including aquatic species.
Life cycles for Kokanee salmon, the landlocked freshwater cousins of coastal Sockeyes, typically run like a fine Swiss timepiece. In this part of the state, mature Kokanee adults depart McPhee Reservoir each fall and swim upstream, battling the Dolores River current, to spawn eggs (females) and milt (males). Insiders call it “the run.”
Spawning begets a new generation, but also means the end of another. Just weeks after the orange bloom of salmon eggs are released and fertilized, the circle of life for the adults is complete and they die.
A similar scenario happens in La Plata County above Vallecito Reservoir.
This season, drought hampered the annual run. Low water levels in the Dolores River posed too great an obstacle.
“The run has been virtually nonexistent,” said Jim White, an aquatic biologist with Colorado Parks and Wildlife. “The way (McPhee) deposits sediment in dry years, it creates a shallow, delta-like area where the river meets the lake. In effect it blocks the salmon from migrating.”
White said such a blockage also occurred in 2002, another year ravaged by drought and wildfires; accumulated layers of mud, silt and debris made the river impassible for the determined Kokanee. This fall only about 150 fish made it through to spawn, a far cry from the usual thousands.
Fertile seasons can yield upwards of 10,000 salmon, White said.
It’s common for Parks and Wildlife staff to harvest catches of fertilized eggs from the Dolores River, incubate them at the Durango Fish Hatchery over the winter and use them for restocking come April. But with mature salmon largely absent this year, they needed a contingency plan.
In October Parks and Wildlife collected eggs from Roaring Judy State Fish Hatchery near Gunnison, and moved them to Durango. The embryonic fish waited there for five to six weeks.
“On average it takes 40 days to reach the developmental stage called eyed-egg stage. You can see the eye of the small fish forming. At that point you can safely transport them,” White said.
Parks and Wildlife released the pea-sized eggs into the Dolores River on Tuesday. After hatching later in December, the battle for survival begins. Many tiny hatchlings can withstand the frigid winter water, White said, because they “hide in little spaces between cobbles and gravel in the riverbed, absorbing the yolk sac. Once they are an inch long they’ll start to drift passively into the reservoir.”
But their small size makes them vulnerable to predation. In the end only a fraction of the stocked fish — “not much above 5 percent,” White said — will arrive upstream to spawn next October.
If there is enough water, that is.