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Lake Wilhelm
Mercer County
Spring 2010 Trapnetting and Night Electrofishing Surveys
Week of April 19th and May 18th, 2010

Lake Wilhelm, a 1,740 acre reservoir, is a large and very popular impoundment located at M.K. Goddard State Park in Mercer County. The Pennsylvania Department of Conservation and Natural Resources (DCNR) owns two thirds of the reservoir (by shoreline measurement) as part of Maurice K. Goddard State Park and the Pennsylvania Game Commission owns the other third as part of State Game Lands 270. The Goddard State Park portion of the lake is restricted to motors with a maximum of 20 horsepower. The state park contains 4 public boat launches, a marina and several car-top/hand launch areas to provide boating and shore fishing access. For anglers who want to improve their fishing opportunities the PFBC Division of Habitat currently posts specific locations of fish habitat structures to download for various lakes throughout the commonwealth which can be found on our website at All species in Lake Wilhelm are managed under the standard regulations for Commonwealth Inland Waters.

Fish Biologist Tim Wilson with a male (left) and female (right) adult walleye

Lake Wilhelm maintains an excellent reputation as a multi-species fishery. It is stocked annually with muskellunge fingerlings along with over one million walleye fry and up to 34,000 one to two inch fingerlings by the Pennsylvania Fish and Boat Commission.

Fisheries biologists from Fisheries Management Area offices at Tionesta & Linesville set trapnets during the week of April 19th, 2010 to evaluate the status of the lake’s fish population and the success of our stocking programs. Our sampling effort consisted of 8 trapnets for 3 nights each equaling 24 overnight net sets with a total effort of 554.91 hours. A total of 4,020 fish representing 13 different species were caught (Table 1). The number of walleye sampled increased since the previous 2004 survey. We captured 108 walleye ranging from 18” to 30” with a large number in the 20” to 24” range (Table 1).

Our results also show a healthy muskellunge population continues to thrive in Lake Wilhelm.  We captured 23 muskellunge ranging from 28” up to 49”. These results continue to indicate that our walleye and muskellunge stocking programs are successful and should continue.

Fisheries Biologist Tim Wilson with a typical Lake Wilhelm muskellunge

Table 1. Length frequency distribution of gamefish captured in trapnets during the week of April 19th.

Size Range (in) Walleye Muskellunge Channel Catfish
15 1
18 3  
19 4  
20 14  
21 14  
22 16  
23 22  
24 13  
25 5  
26 4  
27 5  
28 4 1  
29 3 3  
30 1  
32 1  
33 1  
34 1  
36 3  
37 2  
38 1  
39 2  
40 1  
41 1  
43 1  
46 1  
47 1  
48 1  
49 2  
TOTAL 108 23 1
With respect to panfish, overall abundance and size quality were down since the previous survey in 2004. Bluegill were the predominate panfish species caught in trapnets in 2010 (Table 2). Of the 922 total bluegill caught, the majority of fish were less than 7 inches. Other species of panfish such as black crappie were mostly in the 4-9 inch range followed by white crappie in the 6-11 inch range. As you can see Lake Wilhelm continues to produce abundant numbers of panfish; however, there are fewer large panfish present.

A pair of quality size white (left) and black (right) crappies

Table 2. Length frequency distribution of gamefish and other fish captured in trapnets during the week of April 19th

Species Number Collected  - 2010 Size Range (inches)
Black Crappie 328 2-14
White Crappie 121 2-15
Bluegill 922 3-8
Pumpkinseed 46 2-7
Green Sunfish 1 6
Yellow Perch 28 5-8
Brown Bullhead 171 9-16
Yellow Bullhead 7 9-13
Common Carp 31 24-33
Golden Shiner 58 5-10
White Sucker 216 15-22
Gizzard Shad 1954 3-15
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 spawners”, 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.

Gizzard shad Tub of shad
Representative size Gizzard Shad (left). Collection tub full of Gizzard that dominated our trapnets (right).

We returned to Lake Wilhelm during the week of May 18, 2010 to conduct a night electrofishing survey to assess the largemouth bass population. Over two nights we made 5 runs totaling 3 hours and 16 minutes of electrofishing time and captured 196 largemouth bass for a catch rate of 61.78 per hour. Largemouth bass ranged from 3 to 21 inches and of the total 196 bass, 127 were greater than 12 inches, 59 were greater than 15 inches.

Results from our night electrofishing survey indicate that total catch per effort of largemouth bass was down compared to the previous 2004 survey (Figure 1). However, the abundance of largemouth bass in both the greater than 12 inch and greater than 15 inch categories continues to be close to past results. The lake continues to maintain a great largemouth population with good numbers of larger size bass. Lake Wilhelm’s reputation as being a fertile lake with relatively shallow depths and abundant forage continue to make it a popular destination for anglers wanting to catch a diverse population of species.

Figure 1. Night electrofishing catch rates for largemouth bass from Lake Wilhelm
Figure 1

— Prepared by Brian Ensign, Fisheries Biologist, and Area 1 & 2 Fisheries Management Personnel

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