Whale Rock’s struggling steelhead trout get a biologist’s help

San Luis Obispo city biologist Freddy Otte has set himself a lofty goal — the restoration of a struggling population of landlocked steelhead trout that live in Whale Rock Reservoir near Cayucos.

Otte is doing this by developing a restoration plan to study the Whale Rock steelhead and devise a management plan that will ensure a healthy and sustainable steelhead population in the lake.

“This is a big, big effort,” Otte said. “It is not something we are going to be able to do in a year or two.”

The reservoir is jointly managed by the city of San Luis Obispo, Cal Poly and the California Men’s Colony prison, which use the reservoir as a water source. Otte is passionate about fish biology and is leading the effort.

He faces several big challenges. One of these is four years of drought that have left the lake at 35 percent capacity. These levels are so low that the trout are cut off from the lake’s tributary creeks, which are their preferred spawning habitat.

Disease is another potential threat. Because the steelhead are confined to the Old Creek watershed above Cayucos, there is a real danger that the fish could lose their genetic diversity.

This increases the danger that the entire population could be wiped out if a fatal disease was introduced to the population.

“Genetic diversity greatly increases a species’ resistance to disease,” Otte explained.

But the biggest threat facing the trout is invasive nonnative fish species such as bluegill, bullhead catfish and, most importantly, Sacramento suckers. These invasive fish compete with the steelhead for food and spawning habitat.

There is not much Otte can do about the drought, but there is something he can do about the invasive species. Since July, on a weekly basis Otte and crews of volunteers have deployed two types of traps that target the nonnative fish.

One is a floating trap that catches bluegill, and the other is a 200-foot-long gillnet that targets the suckers. Last Thursday, Otte hauled in the gillnet, which he had deployed near the reservoir’s dam. Six large Sacramento suckers were caught in the net after it had set in the water for 20 minutes.

“These are the guys that we are so valiantly trying to control,” he said holding up a foot-long sucker.

The gillnet is ideal for catching the suckers because it hangs vertically in the water from the bottom of the lake. The suckers are bottom-dwelling fish and easily get caught in the net, but the steelhead swim midway in the water column and rarely get caught, Otte said.

Earlier in the day, Otte had checked his floating fish trap and found that it had caught four bluegill fish. All of the fish that were caught will be placed along the shore of the lake, where they will become food for wildlife such as bald eagles, coyotes and raccoons.

The nonnative fish trapping has been very successful. In the first month alone, 77 bluegill, 11 bullhead catfish and 113 Sacramento suckers were caught.

The challenges for this population of steelhead trout date to 1958, when construction of the Whale Rock Reservoir dam started. The dam cut off access to the ocean for steelhead trout that live in Old, Santa Rita and Cottontail creeks, leaving them trapped in the reservoir. Normally, steelhead live most of their lives in the ocean but return annually to coastal streams to spawn.

“There was a lot of good steelhead habitat here before the dam went in,” said Meredith Hardy, a fish habitat restoration specialist with the California Conservation Corps. Hardy and her CCC crews are helping Otte with the restoration project.

In spite of being landlocked, the steelhead in the reservoir seemed to thrive until recently. Up through the 1990s, anglers were pulling more than 100 trophy-sized trout from the lake each year.

However, in recent years, the number of trout taken from the lake has fallen off dramatically, and those that are caught are smaller.

“They are all of a cookie-cutter size of about 15 to 20 inches when they should be 24 to 28 inches long,” Otte said. “Last year only one steelhead was reported caught from the reservoir.”

The drought and invasive fish species are evidently taking their toll.

Exactly how the invasive fish got into the reservoir is something of a mystery.

The suckers may have been used as bait, and fishermen could have dumped them in the reservoir after a day of fishing. The bluegill and catfish may have escaped from ponds upstream of the reservoir that had been stocked with the nonnative fish.

It is highly unlikely that the nonnative fish will ever be eliminated from the reservoir, Otte said. Instead, the trapping is aimed at keeping their numbers in check so the steelhead can rebound.

In addition to removing the nonnative fish from the reservoir, traps are also useful in studying the steelhead. Those that are captured are measured and scale samples are taken to determine the fish’s age and then the trouts are returned to the reservoir.

The effort started in January when the steelhead began moving toward the reservoir’s tributaries to spawn. This increased the chances of capturing steelhead because the traps were strategically placed in targeted areas, Otte said.

This story was originally published March 7, 2016 at 6:48 PM with the headline "Whale Rock’s struggling steelhead trout get a biologist’s help."