An infestation of hydrilla Hydrilla verticillata caused an 85% reduction in angler effort at Orange Lake, Florida, in 1977 when plant coverage exceeded 80% of the lake. Nonlocal anglers were only 3% of the total number of anglers fishing the lake in 1977, but were 37% of the anglers during 1978 and 1979, when hydrilla coverage was less than 19%. Although angler use of Orange Lake was greatly reduced during the peak 1977 hydrilla infestation, the number of fish caught per hour during 1977 was equivalent to or greater than that of all other study years for all species of sport fish. The almost complete plant coverage did not lower the population of harvestable largemouth bass Micropterus salmoides or black crappie Pomoxis nigromaculatus. Numbers of harvestable bluegill Lepomis macrochirus and redear sunfish Lepomis microlophus were, however, negatively correlated with hydrilla coverage. Reduction in angling caused a 90% loss in revenue from the Orange Lake sport fishery that is valued at approximately $1 million (U.S.) annually. Benefit: cost (B:C) ratios of sportfishing expenditures to aquatic plant control costs during the 2 years in which there were no major aquatic plant problems were estimated to be 300:1 and 69:1. The B:C ratio decreased to 1:1 when hydrilla severely limited access to the lake. Excessive growths of hydrilla, which limited access to Orange Lake, tripled the aquatic plant control costs. These data are offered as an economic case for the control of nuisance aquatic vegetation because the total economic benefits far exceeded the cost of aquatic plant control.
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Colle et al. (1987) studied this question.