Special Walleye Stocking

Spawned this past spring, then raised at the Department of Natural Resources’ Rathbun Hatchery, the 8- to 10-inch advanced fingerlings join walleyes already in Pleasant Creek Lake, Lake Macbride and five other Iowa lakes; introduced as tiny, recently hatched fry.

Each just-stocked advanced fingerling walleye has its left pectoral fin clipped to identify it as it shows up in future population surveys…or on the end of an angler’s line. Each year a different fin will be clipped to mark the year the fingerling was stocked in an ongoing research project on Macbride and six other Iowa lakes.

In contrast, fry stocked in the spring are not clipped or marked each year. Due to their larger size at stocking, advanced fingerlings are expected to survive well and may provide more consistent recruitment of walleyes, year to year.

“We stock many more fry, but they have a higher mortality rate than advanced fingerlings. These advanced fingerling walleyes are more expensive to raise; however, a larger percentage may reach (catchable) size,” explains Rebecca Krogman, DNR reservoir research biologist. “We will be able to determine more clearly several years down the road whether one group grows faster, survives better and ultimately recruits to the fishery more successfully.”

The project will include study of the otoliths, scales and spines, referred to collectively as “age structures,” from a sample of walleyes. The otolith is a sort of fish ‘ear bone’ which shows a record of growth, similar to tree rings.

About 9,400 fingerlings went into Macbride this week. Pleasant Creek received about 4,100. They will grow alongside survivors from 2.8 million Macbride fry and 1.2 million fry in Pleasant Creek.

"Every few years, we hope to get a big walleye year from the fry stockings,” notes DNR fisheries management biologist Paul Sleeper. “If the food source is there, typically zooplankton, the fry get a good start. If we have a cold front moving through, reducing zooplankton growth, we will have poorer survival.”

During these “off years” for fry, the advanced fingerling stocking is particularly important for strategically augmenting walleye populations in Iowa reservoirs.