Some Aquatic Vegetation Changes Following Fish Removal

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Abstract
A semi-quantitative survey of the vegetation of Middle Harbor was made during the growing seasons prior to and following fish removal in Oct., 1948. Before treating the lake with rotenone, a 10-cm. Secchi disc disappeared at a depth of 10 in. in quiet water. In the summer following treatment, the disc was visible in the deepest area at over 4 ft. The frequency of occurrence of 18 spp. of aquatic plants is compared for 1948 and 1949. Only an occasional specimen of Myriophyllum exalbescens, Potamogeton pectinatus, or P. crispus could be recovered by dragging the lake bottom in 1948. In 1949, a wire hoop, 2 ft. in diam. was dropped over the side of a rowboat at 50 ft. intervals. The no. and spp. of plants within the circle were recorded. Chara vulgaris, not found in 1948, occurred in 95% of the samples in 1949. Potamogeton pectinatus, very rare in 1948, occurred in 28%. Naias marina, not found in 1948, occurred in 2%. Myriophyllum occurred in 5%, Potamogeton crispus in 0.1%; neither sp. having made a significant change in abundance. About 6000 Valisneria americana tubers were sown April 24, 1949. The planting appeared successful, although comparable growth was noted in some areas where the tubers were not sown. The above sp. made up about 95% of the bottom vegetation. A sparse growth of emergent and floating leaved species made no significant change in abundance.

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