Might as well post it...
The reason for the decline in size and abundance of the panfish is likely due to the introduction and expansion of gizzard shad in Lake Wilhelm. We do not know how they were introduced into Lake Wilhelm but it may have been from a bait bucket.
Since their introduction in 2004 the population has exploded and was the most abundant species caught in our trapnets. Gizzard shad consisted of 48% of the total fish captured in our trapnets. In 2004 only 4 gizzard shad were caught compared to 1,945 in 2010.
While gizzard shad can serve as an important diet component of larger predators such as largemouth bass, walleye and muskellunge, they also have negative ecological consequences on other species, especially panfish. Gizzard shad are known as “prolific spawnersâ€, meaning they can spawn multiple times for several months producing up to 400,000 eggs and can easily over-populate a lake. Young gizzard shad often out-compete panfish species for food resources such as zooplankton, which can lead to reduced growth rates especially in bluegill and young crappie where food preferences overlap. Reduced growth rates in panfish mean fewer large high quality panfish for anglers.
The PFBC strongly encourages anglers not to release live bait into a lake when fishing to prevent the spread of undesirable or Aquatic Invasive Species.
As can be seen from this catch data, gizzard shad are adversely impacting the panfish fishery. The future is unclear for the recovery of the panfish fishery at this time. We are hopeful that increased predation and competition will reduce the overall aundance of gizzard shad over time and the panfish populations will improve but it is difficult to predict how long this might take. Experience in other lakes with gizzard shad indicate that crappie populations may recover and large crappies may actually use young of the year gizzard shad as forage. It remains to be seen if this can happen at Lake Wilhelm.
http://www.fish.state.pa.us/images/reports/2011bio/2x05_03wilhelm.htm