This is a good read....but is also sad.. One can only guess the negative impact or future impact of the introduction of White Perch and/or "other fish species" introduced on Liberty Prettyboy and Loch Raven ...

Thank you for your inquiry regarding the negative impacts of introduced White Perch.
Let me first say that the Pa Fish and Boat Commission never introduced White Perch to Lake Marburg; therefore, the introduction must have been done by anglers. Unfortunately, anglers did this in a number of southeastern Pa. lakes and even a private lake in York or Adams County, ultimately resulting in undesirable, stunted White Perch dominated fisheries or fish populations. We believe that the introduction to Marburg occurred in the mid to late 1980’s or the very early 1990’s. We found a very sparse population in Marburg in 1993.
Unfortunately, I have a lot of experience with this species and its introduction into lakes and PFBC biologists continue to discover new introductions, even in 2015. There is nothing that we have found that will control their numbers short of a fish kill resulting from disease or starvation. In the mid-1980’s in Lake Nockamixon, Bucks Co. the White Perch consumed most of the available forage including young sportfish and then starved to death. They were in very poor physical condition by fall and died under the ice during the winter. Intensive predator stockings and high natural predator densities have not been enough to reduce or control White Perch numbers over the years when the White Perch populations are growing or reach a large size (Lake Nockamixon in the early to mid-1980’s, Lake Galena, Lake Marburg). White Perch tend to stunt at about 8.5-9.0 inches and have consumed Walleye fingerlings in great quantities during Walleye stockings. In other cases, the White Perch have become established in lakes (Lake Ontelaunee, near Reading; Greenlane Reservoir, Montgomery Co.) that had excellent population and size structures of predators because of limited access for fishing. I would have characterized the lakes as being “predator crowded,” but that was not enough to prevent a White Perch population boom in those lakes that has lasted for decades.
As for the situation in Marburg, I suspect that the Big Bass Regulations and the abundance of White Perch reduced the abundance of Walleye. Our surveys suggested that Walleye reproductive success was on the decline starting in 1994. The Walleye population was being maintained through reproduction from the mid-1880’s through 2000. The year 1994 was the year following the establishment of the Big Bass Regulations and a the year before a very large year class of White Perch was produced (1995). The Big Bass Regulation nearly quadrupled the abundance of bass twelve inches long and longer from 1992 and 1993 to 1997, but this apparently had little impact on the White Perch. The bass population growth alone would have been enough to substantially reduce the Walleye population, however. Also of note is that we were already receiving anecdotal information in about the mid to late 1990’s that the once great Yellow Perch fishery had declined as White Perch abundance increased, but again we can’t say with certainty that the bass did not play a role in this as well. We can say, however, that we have robust Yellow Perch populations in other lakes with large bass populations, suggesting that White Perch were the most likely culprit in the decline of the Marburg Yellow Perch population.
Starting in the 2000’s we substantially increased the Walleye and Muskellunge/tiger muskellunge stocking rates in Marburg. This was not done to control White Perch, but to enhance the Marburg fishery, including the once popular Walleye fishery. Despite the fact that we have now overstocked Walleye based on the thin adults that we sampled this year, there has been no indication that they have exerted any control over the White Perch population, which is what our previous experiences would have suggested.
I hope that the above information will aid you in educating the public regarding the difficulties that White Perch often present when anglers take White Perch introductions into their own hands with little knowledge or concern about the likely consequences for the rest of the fish population and the angling public.
Sincerely,
Michael Kaufmann
Area Fisheries Manager
"This is why you don't stock your own fish.."