The influence of nutria on aquatic vegetation and waterfowl in East Texas

Abstract

The food habits of nutria (Myocastor coypu) and the possible effects of their feeding activities on aquatic vegetation and waterfowl were investigated from April 1977 through April 1979. Study areas were established on Blackcat and Bowfin lakes of Boggy Slough Hunting Club in Trinity County, Texas. Thirty-eight nutria were collected to determine food habits. Stomach contents were analyzed by identifying epidermal cells of the plants eaten. Nutria ate 38 species of plants. The 6 most important food plants as determined by stomach content analysis were panic grasses (Panicum spp.), pondweeds (Potamogeton spp.), spikesedges (Eleocharis spp.), duckweeds (Lemna spp., Spirodela spp., and Wolffia spp.), American waterlily (Nymphaea odorata), and rushes (Juncus spp.). Nutria were eliminated from sections of the study areas by the erection of an exclosure on Bowfin Lake and by trapping and shooting on Blackcat Lake. The response of the vegetation to removal of nutria was monitored on the experimental areas and normal vegetation growth was recorded on a control area where nutria were not removed. From June 1977 to June 1978 emergent vegetation significantly increased by 82% in the nutria exclosure and 61% on Blackcat Lake due to the removal of nutria. Significant decreases in emergent vegetation of 33% on the nutria exclosure and 28% on Blackcat Lake occurred from September 1977 to September 1978. These decreases in emergent vegetation were attributed to dry weather and high plant densities reached in the spring of 1978. An estimate of the nutria population on Blackcat Lake was made using a mark-recapture technique. The estimate was 1 nutria/100 m of shoreline. The food habits of waterfowl on Boggy Slough were evaluated from 44 duck gizzards obtained from hunters during the 1977-1978 hunting season. Food plants in the duck gizzards from Boggy Slough and review of other research on waterfowl food habits indicated that important nutria food plants such as spikesedges and pondweeds were also important waterfowl foods. Nutria also ate plants such as maidencane (Panicum hemitomon) and American waterlily that compete with plants of higher value to waterfowl...