A HISTORY LESSON
June 13, 2001
Taken from Pennsylvania Fish and Boat Commission website http://sites.state.pa.us/PA_Exec/Fish_Boat/pfbchom2.html Options and Recommendations for Trout Management
In the "Ditch" portion of Big Spring Creek, Cumberland County
March 11, 2002
The area of Big Spring Creek known as the Ditch is defined as 150 meters of stream from the source downstream to the base of the former McCracken Dam with an average width of 9.9 meters and surface area of 0.15 ha (0.37 acre). The water level in the Ditch was maintained at an elevated height by placing boards in the spill area of McCracken Dam. This was done to reduce the impact of the water velocity from the perpendicular hatchery discharge into the stream channel and associated erosion of the opposite bank of the ditch. The Ditch area and a short distance downstream of the McCracken Dam to the bridge on Big Spring Creek road were designated as exceptional value by DEP in 1993. Cumberland Valley Trout Unlimited in cooperation with the PFBC habitat improvement section had constructed about 275 feet of mudsill and five wing deflectors to stabilize banks and increase cover for trout.
During the operation of Big Spring Fish Culture Station, this short reach of stream supported an extraordinarily dense trout population that was estimated in autumn 2000 at 805 trout that weighed 1064 pounds. Three trout species, brook, brown and rainbow, occupied the Ditch with about half of the population exceeding 14 inches. Fishing regulations on this section have been Heritage Trout (open year-round, no harvest, barbless flies only) since 1995; prior to this it was designated as Special Regulations that limited harvest to two trout over 15 inches per day. This high density of large trout was very popular with anglers. Angler-use counts conducted from January 1, 1978, through September 30, 1980, on Section 1 that included the Ditch downstream to Thomas Dam indicated an average of one angler per observation during a total of 666 observations. The maximum number of anglers counted at one time was 14. These observations probably does not represent the higher level of angler interest in the ditch subsequent to 1994 cessation of the annual removal of brown and rainbow trout upstream of the Thomas Dam.
With the closure of the Big Spring Creek Fish Culture Station on November 14, 2001, the boards in McCracken Dam that impound the Ditch were removed and the stream surface elevation dropped about one foot. This resulted in exposure of the mudsills with a loss of associated cover and an apparent reduction in numbers and condition of large trout. On-site observations indicated that silt, previously deposited on the streambed while impounded, was transported downstream exposing more gravel. Concurrently, concerns were expressed about the diminished utility of the stream improvement work as cover for trout, and anglers accustomed to deeper water and a higher density of big trout began to complain about lost fishing opportunities.
There are two distinct options for managing the Ditch:
1 The first option would be to manage this segment of stream to enhance natural reproduction of trout. The Commission perceived this as the direction desired by the Department of Environmental Protection and some segments of the angling public. Removal of the boards in McCracken Dam was the first step in the approach to enhancing natural reproduction of trout. Subsequent steps would include removal of the concrete sill and bulkheads in McCracken Dam and possibly removing the concrete weir at the spring.
Following these actions, a habitat enhancement plan was envisioned to contain the stream in a channel with sufficient hydraulic velocity to expose and cleanse gravel substrate, stabilize stream banks and provide a diversity of habitat, especially spawning sites and nursery areas, for a fully age-structured population of trout resulting from natural reproduction. Recovery of emergent and submerged aquatic vegetation would be expected to be associated with the lower water level and stable substrate to enhance cover for all life stages of trout. Based on prior studies of the wild trout population in Big Spring Creek in the vicinity of, but downstream from, McCracken Dam, the weight of naturally reproduced trout in the area of the ditch (about a third of an acre) would potentially range between 50 and 100 pounds.
2 The second option would be to manage the Ditch as habitat for larger trout. This would be approached by restoring the boards to McCracken Dam and thus increase the water depth to restore the cover provided by the mudsills. Increasing the habitat for large trout and sustaining a population with a high proportion of large trout has been an approach advocated by both the Big Spring Creek Watershed Association and Cumberland Valley Trout Unlimited.
Increasing the habitat for large trout by impounding the water at McCracken Dam will be contrary to optimizing the stretch for natural reproduction of trout because it will result in silting of spawning gravel, it will reduce nursery habitat and limit emergent aquatic vegetation. Periodic removal of the boards to remove silt buildup would adversely affect the capacity of the habitat to hold large trout while lowered and would not be expected to mitigate for the loss of nursery habitat.
In addition, we should have no expectation that replacing the boards in McCracken Dam will restore the size and abundance of large trout in the ditch that were present during the hatchery operation (in autumn 2000, 800-plus trout weighed over 1000 pounds). The big trout in the ditch were sustained by the productivity of the water discharged from the Big Spring Fish Culture Station and the numbers of trout in the ditch were sustained by escapement of trout from the hatchery. If these efforts to manage the area for large trout were to be successful in maintaining one-third of the levels that were present with the hatchery discharge, it would be remarkable.
The Bureau of Fisheries is pursuing the second option in attempting to manage the "Ditch" for large trout by restoring the boards in McCracken Dam with sufficient height to wet the logs on the mudsills (about 12 to 15 inches). Downstream of McCracken Dam, we will continue to use approaches optimizing natural reproduction of trout and a fully age-structured population of wild trout. The Division of Fisheries Management will continue to monitor the fishery in Big Spring Creek, including the ditch, to assess the success of the management actions that have been and are being implemented to restore natural reproduction and sustain angler use.
PFBC Required to Eliminate Discharge by July 1
Big Spring Hatchery Will Likely be Closed
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