BIOLOGIST REPORT

Blue Marsh Reservoir


Blue Marsh Reservoir is a 1,150 acre impoundment constructed in 1974 by the 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 reservoirs primary function is flood control followed by water supply, water quality control, and recreation. Blue Marsh Reservoir experiences a 5 foot draw down each winter to provide flood protection to downstream areas. Additionally, the reservoir depth can fluctuate throughout the year depending upon climatic conditions.

The Pennsylvania Fish and Boat Commission (PFBC) has sampled the largemouth and smallmouth bass populations of Blue Marsh Reservoir annually since 1988. Based upon the physical features of the lake and the corresponding fish habitat that is provided the reservoir is divided into two sampling zones. These sampling zones are defined as up lake, which includes the no-wake zone (the Tulpehocken and Spring Creek coves) and down lake, which includes the remainder of the reservoir. Although both largemouth and smallmouth bass can be found throughout the reservoir, largemouth bass are the dominant bass species in the up lake zone while smallmouth bass tend to be more readily available in the down lake zone.

Blue Marsh Reservoir has been managed with more restrictive bass regulations (15 inch size limit, 2-4 fish creel limit) since first being placed in the Conservation Lakes Program in 1987 and more recently (1994) as part of the Big Bass Program. The PFBC uses a set of standards based on electrofishing catch rates to determine if a lake maintains a “quality” bass population. These standards may also be used to measure whether or not the application of a management technique, such as Big Bass, improves the quality of a bass population. These standards are based on the number of bass collected per hour of electrofishing effort and are defined as a minimum total catch of 35 bass/hr, a minimum catch of 7 bass/hr > 12 inches, and a minimum catch of 3 bass/hr > 15 inches. Continued annual monitoring of the Blue Marsh bass population has shown variation in the population with the catch rates dipping below these standards in some years. Although catch rates during the late 1990's indicated a decline in the population there was an overall positive trend in all three electrofishing catch rate indices from 1988 to 2001. Some of the decline in the catch rates during the late 1990's and early 2000's may have been attributable to poor survey timing. This poor timing was the result of mandated Delaware Estuary striped bass survey assignments for the PFBC area staff that did not allow for the flexibility in scheduling the Blue Marsh Reservoir survey work when environmental conditions (water temperatures) were optimal. Some of the decline in the catch rates may have also been attributable to natural variation in the population and a 1998 fish disease outbreak in the adult bass population.

Catch rates have been consistently higher in the up lake zone compared to the down lake zone since 1988. Additionally, the up lake catch rates have typically exceeded the minimum electrofishing catch rate standards for a quality bass population (see figures below). Catch rates in the down lake zone have remained below the standards for total catch and have fluctuated above and below the standards for fish > 12 inches and fish > 15 inches. When comparing Blue Marsh Reservoir's bass population to other lakes in southeast Pennsylvania we found that Blue Marsh's population was below average for the total electrofishing catch and the catch of fish > 12 inches long and was above average for the catch of fish > 15 inches long (see table below).

  Up
Lake
Down
Lake
Total
Lake
Bass
Standards
SE PA
Average
Total Catch 35.0 18.0 25.6 35.0 50.1
>= 12 in. 14.9 5.4 9.5 7.0 12.1
>= 15 in. 6.6 2.7 4.4 3.0 3.5
Table 1. Average catch rate (#/hr) of black bass captured during annual electrofishing
at Blue Marsh Reservoir from 1988 - 2001.

cpue of black bass - total

 

cpue of black bass >= 300mm

 

cpue of black bass >= 375mm

-- Area 6


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