Biologist reports logo Blue Marsh Reservoir
Berks County

2006 Crappie Survey


Blue Marsh Reservoir is a 1,150-acre impoundment constructed in 1974 by the US Army Corps of Engineers (ACOE) on Tulpehocken Creek in western Berks County. The reservoir is located approximately 6 miles northwest of the City of Reading and is partially bordered by State Route 183. As an ACOE impoundment the primary function of the reservoir is flood control followed by water supply, water quality control, and recreation. Blue Marsh Reservoir experiences a five-foot draw down each fall and winter to provide flood protection to downstream areas. Additionally, the reservoir depth occasionally fluctuates depending upon climatic conditions.

Blue Marsh Reservoir has been managed with more restrictive crappie regulations (9 inch minimum length limit, 20 fish/day creel limit) since being included in the Panfish Enhancement program beginning in 2000. The Pennsylvania Fish and Boat Commission has placed trap nets at the same locations to monitor the crappie population (both black and white crappie) of Blue Marsh Reservoir for 19 out of 24 years between 1982 and 2006, inclusive. The 2006 survey was conducted from May 30 to June 1 to coincide with crappie spawning.

Three legal size white crappie
Three legal size white crappie

Nearly annual monitoring of the crappie population beginning in 1985 showed substantial variations in abundance throughout the 1980’s and early 1990’s. Fluctuations in the total trap net catch per hour (CPUE), which was used as an index of crappie abundance, were not nearly as great from 2001 through 2006. The crappie population density remained below the average CPUE for southeastern Pennsylvania lakes since 2001 (Fig. 1); however the lake remains a popular crappie fishery for legal size fish.

The CPUE of crappie less than 6 inches in length was used as a “recruitment” index of reproductive success and survival of young crappie. Recruitment was low in the 1980’s through the early 1990’s before improving in the mid through late 1990’s. Crappie recruitment declined in the late 1990’s and after 2001 was at or below the average for lakes sampled in southeastern Pennsylvania (Fig. 2). While overall crappie recruitment was acceptable throughout the 2000’s, white crappie reproductive success appeared to have been poor in 2005. The excellent recruitment in 1997 and 1998 (corresponding to 1998 and 1999 in Figure 2) was expected to result in a high trap net catch rate of crappie > 9 inches long in 2000 and 2001; however, the catch of crappie > 9 inches long declined in 2000 and 2001 (Fig. 3). This was an indication that mortality (natural & angling), possibly including a November, 1998 fish kill, had combined to reduce the number of crappie that had survived to reach 9 inches in length. Even though the catch rate of 9 inch and longer crappie had declined it remained above the SE PA average CPUE > 9 inches.

Crappie populations tend to be cyclic by nature with strong year classes followed by weak year classes. During the periods following the production of weak year classes there are fewer fish in the population and harvest by anglers may exacerbate the situation by making it more difficult for the population of legal size fish to rebound. By increasing the minimum length limit and reducing the creel limit for crappie in Blue Marsh Reservoir biologists are attempting to lessen the extremes between the peaks and valleys of the crappie population through protection of multiple year classes (cohorts) of young fish, thereby maintaining a more consistent crappie population and providing a more reliable fishery, especially for quality size fish. Continuing trap net surveys are providing biologists with the opportunity to determine if the Panfish Enhancement regulations are successful in dampening the degree of variation inherent in crappie population abundance, ultimately to improving the quality of the crappie fishery at Blue Marsh Reservoir.

During the 2006 survey a total of 308 crappie were collected between 3 and 15 inches long. Seventy-nine met or exceeded the nine-inch minimum length limit. Other fish species collected included 3 walleye up to 23 inches long, 29 channel catfish up to 27 inches long, numerous bluegill, mostly between 4 and 5 inches long, and 9,297 alewife. In addition, the capture of six striped bass hybrids between 6 and 12 inches long suggested that survival of stocked fingerlings has been good in recent years, given that they have been uncommon in previous trap net catches.

23-inch walleye with numerous alewife in the background
23-inch walleye with numerous alewife in the background

Three channel catfish over 20 inches
Three channel catfish over 20 inches

Key to Figures: Fisheries Biologists use the term catch per unit of effort (CPUE) to quantify their catch. For trap net surveys the CPUE is simply the number of fish collected for each hour the trap net is fished. For example: if a net is fished for 20 hours and captures 100 crappie the CPUE is 5.0 crappie/hr.

Figure 1

Figure 2

Figure 3

 
-- Bryan Chikotas, Area 6 Fisheries Technician

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