Action: Reduce adverse habitat alterations by excluding problematic aquatic species
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A replicated paired study in the USA found that waterbirds preferentially used wetland plots from which grass carp Ctenopharyngodon idella were excluded but moved as these became depleted over the winter.
Many of the most destructive invasive species are aquatic, for example zebra mussels Dreissena polymorpha and grass carp Ctenopharyngodon idella. Excluding such species has unique difficulties, but it may be possible to maintain small areas without them.
Supporting evidence from individual studies
A replicated, paired study in the winters of 1993-1995 in six sites in an open-water refuge in Alabama, USA (Benedict & Hepp 2000) found that waterbird density in October was higher in plots with grass carp Ctenopharyngodon idella excluded, but that birds moved to plots with carp present over the winter. Exclusion plots had higher levels of native vegetation (dominated by muskgrass Chara spp. and sago pondweed Potamogeton pectinatus) but birds left as this became depleted. Control plots were dominated by (non-native) milfoil Myriophyllum spicatum. Exclusion plots were established to re-establish native species using netting (1.27 cm2 mesh, 1.2 m tall) held in place by buoyant ropes and weighted with steel rods to create 0.1 ha plots (25 x 50 m). Identical plots (without netting) were created (? 25 m away from the native plot) in areas of 100% milfoil coverage.