DNRE Continues Reduced Walleye Stocking

March 30, 2010

Walleye are among the most popular cool-water game fish in Michigan, prized both for their sporting characteristics and as table fare. Numerous walleye fisheries have been developed over the years by stocking hatchery-raised fry into lakes and rivers. But because of fish disease issues, Michigan's walleye-stocking program has been reduced significantly in the last couple of years.

As in the past two years, the Department of Natural Resources and Environment's Fisheries Division will again produce fewer walleye fry this year than it did in the past as a precaution against spreading of viral hemorrhagic septicemia (VHS). Fisheries Division is taking precautions not to expose its hatcheries to the virus or to spread the disease to additional water bodies in the state of Michigan.

VHS is a disease that infects numerous fish species, causing them to die from internal bleeding. The disease manifested itself most spectacularly in 2006, when an estimated 2,000 to 4,000 adult muskellunge fell to the disease in Lake St. Clair and the Detroit River. The disease also killed a number of species of fish - including walleye and yellow perch -- in Lake Erie and whitefish in Lakes Huron. VHS has been detected in two inland lakes (Budd Lake in Clare County and Baseline Lake in Washtenaw County). VHS killed fish in Budd Lake in 2007.

Although fisheries biologists have made progress toward developing protocols to disinfect fish eggs for cool-water species such as walleye - those protocols already exist for salmon and trout - they are not yet proven. Until a reliable disinfection process has been proven, the DNRE will not risk exposing its hatchery system or other bodies of water to VHS.

Little Bay de Noc and Muskegon River walleye will again serve as brood stock areas for this year's walleye production. Although routine testing of walleye from the Tittabawassee River has failed to turn up evidence of VHS in those fish, previous samples of Lake Huron walleye have tested positive for the virus. Fisheries biologists believe it not worth the risk to collect eggs and milt from Tittabawassee River fish to be used in the stocking program at this time, especially as the demand for walleye fry is at a lower level because of the reduced stocking policy. Tittabawassee River walleye, however, will be evaluated as a potential source of brood stock for the 2011 stocking season.

Walleyes from brood stock waters will be tested for VHS prior to egg-take. All walleyes that are captured for their eggs and milt will be sacrificed to collect organs for further VHS testing. In addition, ovarian fluids and milt samples will be collected to be used in experiments to see if a non-lethal testing procedure using these samples is as accurate as using organ samples.

Walleye eggs will be incubated and hatched at the Thompson State Fish Hatchery in the Upper Peninsula, where the walleye operation can be segregated from coldwater production operations. (The department is evaluating another facility in Mason County, outside the hatchery system, for this purpose, too.)

Fry hatched at Thompson will be tested for the virus, but the tests will not be completed by the time the fry are mature enough to be moved to rearing ponds. However, the testing will allow hatchery personnel to track transmission of the virus, should those tests prove positive. If so, those fish will be destroyed.

No fry will be shipped to the Lake Superior Basin in 2010. The same ponds that were used for walleye rearing in 2008 and 2009 will be used again. Those ponds are all isolated from other water bodies, have no inlets or outlets, and are not drainable.

No walleyes will be stocked in the Lake Superior Basin. Only waters in the Lakes Michigan, Huron or Erie Basins that were approved for stocking in 2008 or 2009 will be eligible for fish this year, unless fisheries managers can demonstrate a very low risk of spreading the virus. Fisheries managers will prioritize waters to receive fish by June 1.

Although the DNRE has identified several possible additional bodies of water for walleye stocking, they will not be stocked unless a rapid-testing procedure is developed prior to stocking. It is the DNRE's plan to gradually resume walleye stocking in additional waters once rapid-testing and egg-disinfection protocols are developed.

"We'd like to begin ramping up production and return to our previous stocking levels, but we're not going to jeopardize infecting our hatchery system or spreading VHS virus further," explained Gary Whelan, who oversees fish production operations for the DNRE. "We're optimistic that a disinfection protocol and a rapid-testing procedure can be developed that will allow us to return the program to its former capacity in the near future."