Fish trouble: Invasive tui chub back in Diamond Lake

Oregon Department of Fish and Wildlife biologists discovered one tui chub in a trap net during ongoing fisheries monitoring at Diamond Lake in mid-October.

Fisheries professors at Oregon State University confirmed the fish was a tui chub, the first seen in Diamond Lake since the 2006 rotenone treatment that eliminated about 90 million of the invasive minnows.

ODFW said Tuesday it believes that once again, tui chub were used illegally as live bait fish or were intentionally reintroduced into the lake.

“This is extremely frustrating, when you consider the amount of time and effort put into the restoration of Diamond Lake by so many,” said Greg Huchko, ODFW Umpqua District Fish Biologist. Huchko said the chub was about seven and a half inches long and is likely a six-year-old fish.

ODFW said it will increase sampling and work with its partners, the Umpqua National Forest, Oregon Department of Environmental Quality and Douglas County to develop and implement a joint action plan for 2016.

The plan would include monitoring for additional tui chub, tracking population changes if detected, and determining management options including possible changes to trout stocking strategies and implementing chub spawning disruption.

“This is a very troubling discovery that the Forest Service is going to work to address adaptively with ODFW and other partners,” said Jason Wilcox, Fisheries Program Manager with the Umpqua National Forest.

ODFW has conducted invasive fish monitoring each year since the rotenone treatment and in 2008, golden shiners – another small bait fish – were discovered in Diamond Lake.

ODFW sampled via electrofishing and/or conducted additional netting each year to evaluate golden shiner population numbers.

The agency has also removed shiners from the lake, disrupted possible shiner spawning, and checked for tui chub presence. Hundreds of juvenile golden shiners have been sent each year to OSU for positive identification and none were found to be tui chub.

Diamond Lake’s benthic macroinvertebrate population and zooplankton composition have remained healthy, the agency said, and trout condition factors have also indicated the stocked rainbows have an abundant food supply and the fishery has not been negatively impacted by golden shiners or the recently discovered tui chub.

ODFW has also stocked predacious strains of rainbow trout as called for in the 2004 Diamond Lake Restoration Project Final Environmental Impact Statement. ODFW, the Umpqua National Forest, Oregon State Marine Board and Douglas County conduct extensive public outreach with Diamond Lake visitors on the perils of aquatic invasive species. This outreach includes education, boat washing stations, boater surveys, and contact with anglers.

In September 2006, ODFW successfully treated Diamond Lake with rotenone, ridding the lake of an estimated 90 million tui chub and restored its water quality and recreational rainbow trout fishery.

The nearly $6 million treatment followed years of effort and collaboration among ODFW, the Umpqua National Forest, Oregon Department of Environmental quality and other agencies in the Diamond Lake Working Group.