Evaluating a Rapid Aerial Survey for Floating-Leaved Aquatic Vegetation

Aerial surveys are a valuable tool for monitoring wildlife and their habitats throughout North America, but manned aerial surveys for monitoring aquatic vegetation communities have seldom been evaluated rigorously. We used a fixed-wing aircraft and modified double observer method to survey an invasive aquatic macrophyte, water hyacinth (Eichhornia crassipes), and other floating-leaved aquatic vegetation along Illinois River to evaluate detection probability and error associated with size, extent, and species identification during aerial surveys. Generally, error rates for species identification (range = −3.7% − 1.0% mean error) and extent (x− = 2.2 ± 2.2% error) were low, but aerial estimates of bed size (x− = −0.65 ± 0.17 ha mean error) were less accurate. Aerial surveys were rapid (< 6 h/survey) and achieved reasonable estimates of species identification, species composition of beds, and bed size when beds were >0.04 ha. However, size estimates were much less accurate when beds were <0.04 ha. If precise spatial data are required, especially for small beds of aquatic vegetation, remote sensing technology and ground-surveillance may be better options than high-speed aerial surveys. However, census-style aerial surveys provide a cost-efficient and rapid technique for estimating coverage of large (>0.04 ha) beds and tracking occurrence of individual species of floating-leaved aquatic vegetation.