Arguably Pennsylvania's most important inland walleye lake, the population at Pymatuning has been in a tailspin in recent years.

Anglers first noticed a change in the dynamics of the lake's walleye fishery five years ago. Once known for its ability to produce big numbers of relatively small fish, Pymatuning has shifted to fewer, but larger, walleyes.

Going back to sampling work done by the Fish and Boat Commission in 2003, the majority of the walleyes collected were greater than the 15-inch minimum length limit.

On a short-term basis, this wasn't seen necessarily as bad news, particularly by the anglers who adapted their techniques to successfully catch these larger fish.

Unfortunately, few young walleyes from fry-stage stockings were surviving to replace the older, legal-sized fish.

In a survey conducted last spring on Pymatuning, a total of 917 walleyes were captured. Legal length fish made up more than 98 percent of the catch.

Of those, 71 percent of the fish were more than 18 inches and 32 percent exceeded 20 inches. The longest walleye collected measured a bit more than 28 inches. Trapnet hours during the 2006 survey were 785.25.

When you consider the findings of the 2003 survey, it would indicate the overall walleye population has fallen. During the '03 survey, which entailed 1,766 trapnet hours, roughly 2.25 times that of the '06 effort, 5,173 walleyes were captured. Of those, 87 percent in '03 were over the legal length.

Many variables occur during sampling efforts, with weather conditions being the most significant. So perhaps it's not completely valid to suggest Pymatuning's walleye population is now half of what it was in 2003.

However, lake sampling conducted in 2004 and '05 also illustrate the trend of a rising percentage of legal-sized fish, but fewer overall.

While some natural reproduction might occur in Pymatuning (Ohio Division of Wildlife biologists, who also manage the lake, claim there is a low level of reproduction), by and large the lake's walleye fishery is fueled by stockings of walleye fry.

Though the number of stocked fry varies from year to year, the number is always in the millions. Throughout the 1980s and '90s fry stockings maintained a good walleye fishery. Fry, at the traditional life stage as stocked by the commission, are three days old.

Two primary factors affecting the survival rate of walleye fry are the amount of plankton found in the lake at the time of stocking and the density of predators that feed on the freshly stocked fish.

Zooplankton, which provide food and cover for freshly stocked walleyes, is dependent on the weather. Stable, warming spring weather is good for zooplankton production, while during cold, rainy conditions the opposite is true.

Predators, which include alewife herring, are known to feed on and significantly affect stocked walleyes. Alewife are present in Pymatuning, and many anglers say they believe alewife numbers have risen dramatically.

Last spring, the commission began stocking advanced-stage fry with the hope the fish would experience the same excellent survival rate in Pymatuning as they did in hatchery ponds.

Fisheries manger Allen Woomer said regular fry are stocked within a few days of hatching, but advanced fry are stocked about three weeks after hatching. They are fed brine shrimp in the hatchery to sustain them to an advanced size

Woomer said the fall young-of-the-year survey done last year did not cause reason for optimism, at least from the initial stocking effort. He said advanced fry stocking produced about the same level of fall fingerlings in the lake as normal fry stockings did.

"At this point, the advanced fry have not performed any better than the regular fry," Woomer said. "We will continue to evaluate advanced fry stockings versus regular size fry for the next few years and hope to have a better return in the future."

Jeff Knapp is an outdoors writer for the Butler Eagle.