BIOLOGIST REPORT

Blue Marsh Reservoir

2002 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 used trap nets set at the same sites to monitor the crappie population (both black and white crappie) of Blue Marsh Reservoir for 14 out of 21 years between 1982 and 2002, inclusive. The 2002 survey was conducted from June 3 to June 5.

Fisheries Management crew pulling trap net
Fisheries Management Crew Pulling Trap Net

Nearly annual monitoring of the crappie population beginning in 1985 showed dramatic 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 drastic in the late 1990’s through 2002; nevertheless, the population appeared to be on a steep decline. The crappie population density in 2002 remained similar to those in the average southeastern Pennsylvania lake, however (Fig. 1).

The CPUE of crappie less than 6 inches long 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. Although recruitment declined in the late 1990’s and 2000’s it still remained near the average for lakes sampled in southeastern Pennsylvania (Fig. 2).

The excellent recruitment in 1997 and 1998 (corresponding to 1998 and 1999 in Figure 2) was expected to result in a high 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 fishing mortality and/or natural mortality, 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 similar to other lakes surveyed in southeastern Pennsylvania during the past two decades (Fig. 3). Those lakes did not have crappie specific protective regulations, however.

24 inch walleye
24 Inch Walleye

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 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. Additional trap net surveys in the years to come will allow biologists to determine if the Panfish Enhancement regulations are successful in improving fishing opportunities for crappie at Blue Marsh Reservoir.

23 inch channel catfish
23 Inch Channel Catfish

During the 2002 survey a total of 378 crappie were collected between 3 and 14 inches long. Only 34 met or exceeded the nine-inch length limit. Other fish species collected included 4 walleye up to 24 inches long, 38 channel catfish up to 23 inches long, numerous bluegill mostly between 4 and 5 inches long, 8,708 alewife, and a 34 inch tiger muskellunge that had successfully escaped with an angler’s spinner-bait.

Tiger muskellunge with spinner bait in upper jaw
Tiger muskellunge with Spinner Bait in Upper Jaw

Close-up of tiger muskellunge and spinner bait
Close-up of Tiger Muskellunge and Spinner Bait

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 - PA trap net CPUE (#/hr) of all crappie captured from Blue Marsh Reservoir

 

Figure 2 - PA trap net CPUE (#/hr) of crappie < 6 inches long captured from Blue Marsh Reservoir

 

Figure 3 - PA trap net CPUE (#/hr) of crappie >= 9 inches long captured from Blue Marsh Reservoir

-- Area 6


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