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.