Biosurvey and Biomanipulation

Culver Lake

Culver Lake BiosurveyCulver Lake, a 550-acre, 65-foot deep lake is located in Sussex County, NJ.  Through the 1960s and into the 1980s the lake’s water quality had declined, negatively affecting its recreational use. This occurred even though total phosphorus concentrations were low, usually < 0.04 mg/L and watershed development minimal.  Princeton Hydro’s data showed that the lake’s problems were largely the result of excessive numbers of the filter feeding fish, alewife.  These fish had been stocked by the State in the 1950s to support the lake’s trout fishery.  Princeton Hydro initiated a series of fishery surveys designed to investigate the merits of a biomanipulation restoration program to address and correct lake water quality impacts directly related to the historic introduction of alewife.  Biomanipulation is a “top down” restoration technique that improves water quality through management of fish and zooplankton as compared to a “bottom up” approach that manages nutrients and phytoplankton.

The sampling activities implemented by Princeton Hydro involved the collection of plankton data using a variety of towed nets and traps and the sampling of the fishery community using a variety of passive and active gear: trap nets, gill nets, mid-water trawls, and electro-fishing equipment.  The data were synthesized and analyzed using various fishery statistics.  The results were then used to design a fish and zooplankton stocking program for Culver Lake.

Under Princeton Hydro’s direction both brown trout and hybrid striped bass were stocked to recreate a “two-story” fishery capable of heavily feeding on the problematic alewife.  Data obtained through post-stocking fishery studies documented the successful reduction of the lake’s alewife population.  With the alewife under control, Princeton Hydro then began stocking the lake with zooplankton.  This involved the introduction, over a three-year period, of Daphnia and Ceriodaphnia, large zooplankton that are very adept at keeping phytoplankton densities in check.

Data collected since the completion of the biomanipulation projects show the lake’s water quality has dramatically improved, all without using copper-based algaecides to control algal blooms.  Secchi depth transparency increased from a summer mean of less than one meter to over three meters, algal blooms significantly diminished, and the lake’s zooplankton community shifted from small-bodied, omnivorous forms to large-bodied, herbivorous forms. This also resulted in improvements in the lake’s recreational fishery; the lake holds the State’s record for the largest hybrid stripe bass captured by a recreational angler.