Glenwood, Minn. A fisheries biologist in Glenwood is
coordinating a statewide study of walleye stocking strategies that
may result in changes to the DNR’s decades-old procedure of rearing
walleye fingerlings in natural ponds.
DNR biologist Brad Parsons says 50 Minnesota lakes ranging from
200 to 1,000 acres are being stocked with walleye fry, “frylings,”
and fingerlings to determine the effectiveness of each in varied
waters. The goal of the study, he says, is to improve the overall
efficiency of the walleye stocking program.
“Area fisheries managers are responsible for so many individual
lakes that they often don’t have time to evaluate stocking
techniques,” Parsons says. “We hope to give the managers a starting
point for their stocking strategies.”
Another reason for the study is to look at alternatives to the
DNR’s practice of rearing walleyes in natural ponds, which is
criticized for inconsistent annual production and possible harmful
effects on pond ecology, particularly for waterfowl. Neighboring
states raise small walleye fingerlings, which the Minnesota DNR
calls “frylings,” in artificial, hatchery ponds. The DNR has stayed
away from hatchery walleye production, saying the natural pond
method is cheaper and produces a large fingerling more likely to
The study is designed to determine how well the various stocked
walleyes survive in lakes that are representative of the state’s
typical stocked walleye lakes. All the fish in the study are marked
as fry with a chemical called oxy-tetracycline, which biologists
can later find as a fluorescent ring in a walleye’s otolith, or ear
bone, using a special microscope outfitted with ultraviolet
“It’s a good, cheap way to mark huge numbers of individual
fish,” Parsons says.
The 50 lakes in the study initially were divided into groups of
10 that received five different walleye stocking “treatments” in
One treatment consists of stocking newly hatched walleye fry at
a rate of 1,000 per littoral acre (the area in a lake less than 15
feet deep). Three treatments are stocking pond-reared fingerlings
at rates of one-half, one, and two pounds per littoral acre. The
frylings are stocked at 150 per littoral acre.
Totals for the project’s 2001 stockings were 2.8 million fry,
220,000 frylings, and 5,400 pounds of fingerlings, or about 79,000
The 50 lakes will be stocked with a different treatment, picked
at random, in 2003. Parsons said researchers skipped a year between
stockings to avoid suppression of the second treatment by the
year-class from the first stocking. Total numbers of fish stocked
will be similar to 2001.
Although autumn electro-fishing has occurred to monitor survival
of the stocked walleyes, gill net assessments will be the main
evaluation tool. The first netting is scheduled for 2004, when
walleyes from the 2001 stocking will be three years old.
Another netting is scheduled for 2006, when fish from the second
stocking reach age three. Parsons hopes to have final results from
the study by 2007. However, if necessary, he is prepared for a
third stocking in 2005 and a netting in 2008.
The study is larger in geographic scope and of a shorter time
duration than some stocking studies. Parsons says this large-scale
study is designed to overcome natural variations due to weather or
If the frylings are successful, changes could result in the
state’s walleye rearing program perhaps including the construction
of one or more walleye hatcheries. Frylings for the study were
produced at artificial ponds at the DNR’s Waterville hatchery
facility and at the Blue Dog Hatchery in northeastern South
Unlike neighboring states, Minnesota presently doesn’t have
facilities to produce large numbers of frylings.
Frylings are produced within a few weeks during spring and early
summer. Fertilized walleye eggs are hatched and the resulting fry
are stocked in artificial ponds. By late June, they grow to about
an inch and a half in length. The ponds are drained and the tiny
walleyes are harvested for stocking. At this size they are large
enough to avoid small predator fish such as bluegills.
Parsons says the frylings present some challenges for stocking.
Water temperatures in late June are often very warm, which makes
fryling survival during transportation and stocking somewhat risky.
South Dakota biologists have told him the key seems to be handling
the frylings while they are still eating plankton, rather than
after they’ve switched to a fish diet. In the earlier stage they
are more tolerant of high water temperatures.
So far, Parsons says the frylings have had excellent survival
during transport. Electro-fishing has also determined the stocked
frylings have survived.
Just how their survival compares with fry and fingerling
stockings may well guide the future of walleye stocking in the
state. If frylings prove effective, the question of whether
Minnesota should invest in one or more walleye hatcheries will move
forward. Costs, both of the construction of the infrastructure and
for transporting hatchery-produced walleyes to various locations,
must be addressed.
Despite its drawbacks of inconsistent production and ecological
concerns, the present natural pond rearing system gives fish
managers locally available walleye fingerlings, which can be fairly
inexpensively harvested and moved to lakes for stocking.