Kokanee still on the brink

If we want more kokanee to spawn in Mission Creek, we’ll have to reverse the damage done to its spawning habitat, says a leading biologist.

About 1,500 kokanee are now spawning in Mission Creek at the peak of their annual migration — a tiny fraction of the 300,000 to 500,000 that reproduced there in the 1970s. Dr. Peter Dill, a fish-biology professor at Okanagan University College, attributes the rapid decline to the diking system along the creek, which has washed out gravel that’s crucial to the eggs’ survival.

“The gravel in the creek is pathetic. The creek needs to be improved,” Dill said Sunday. “I think the kokanee are a tragic illustration of our failure to put environmental considerations right in front of the planning process.”

To prevent Kelowna from flooding, engineers built dikes at the lower end of the creek and pushed large boulders to the side. The dikes are built too close together to allow the creek to meander and form natural gravel beds ideal for building kokanee nests, said Dill.

When the water’s high, the dikes create a long, straight, smooth-bottom ditch, and the current scoops out the gravel.

“There’s no room for the creek to move,” he said. “If there was no dike, or they were set back further, the stream would move back and forth between the dikes and you’d create spawning habitat. But it’s very hard to correct that.”

Twenty years ago, 90 per cent of all the kokanee in Okanagan Lake spawned in Mission Creek, the lake’s largest source of water. Dill now estimates the creek provides habitat for 30 to 40 per cent of the lake’s kokanee.

He suggests dropping large rocks into the creek at certain intervals. They’d create the turbulence and variety in water flow, and generate a diverse habitat — including gravel.

Boulders have been effective in other systems, says Brain Jantz, fisheries technician with the Environment Ministry. But if they’re too large in Mission Creek, logs and other wood drift can get hung up and cause flooding, he said.

Human development has virtually robbed the kokanee of the water and habitat they need. The creek provides water for agriculture and domestic use, and homeowners live on its banks.

“It’s a huge problem because of all the urbanization that takes place on either side of the stream,” said Jantz. “In some cases, you can’t move the dikes back because it encroaches on private property.”

Seven kilometres upstream from the creek mouth is a spawning channel built in the 1980s. Its bottom is covered in clean gravel that looks ideal for egg-hatching. Yet fewer than 150 spawners were in the channel on Sunday. Most of the fish traditionally spawn below the seven-kilometre mark, where there’s little gravel to lay eggs on.

The Environment Ministry has considered building a spawning channel closer to the creek mouth.

“But if the fish aren’t using the habitat in this channel, why go to that trouble?” said Jantz. “In a perfect world, this system would have been designed with dikes set back further to allow the stream to operate naturally and retain its gravel.”

Meanwhile, smaller waterways like Peachland Creek and Powers Creek attract more spawners because sports clubs have dumped gravel and created better habitats. But they don’t have enough spawning habitat to pick up the slack in Mission Creek.

“Mission Creek is going down faster than other creeks, which means it’s not being maintained properly,” Dill said. “It’s a political issue. Mission Creek is the major supplier of water for the Okanagan … The needs of water management are in conflict with the needs of fish.”

The Environment Ministry blames the mysis shrimp for the kokanee’s decline. Introduced as a food source in the 1960s, the tiny crustaceans now compete with young kokanee for plankton. Three trawlers are now dragging nets in the lake to determine whether a commercial mysis fishery is feasible.

Dill argues there’s little evidence to prove the shrimp are killing off the kokanee.

“If mysis are part of the problem, and we get rid of them, where are the fish going to spawn? We have such a mess in this creek … Deal with Mission Creek first, and then the mysis.”