In response to such threats, cooperative research on hydrology and biotic responses is being conducted, and researchers are developing models to predict water flow under various conditions. These tools have helped park managers negotiate better schedules for water release from the South Florida Water Management District to the national park. Research also is under way to assess the effects of agriculture, in part to determine how water coming from agricultural areas north of the Everglades and coursing through canals to the park threatens to increase the amount of phosphates and nitrates in park wetlands. Other research is being done to determine the effects of sport fishing, which has grown by almost 10 percent each year, and the associated effects of the increase in recreational boat use on the seagrass beds. These efforts and others in the park should increase our understanding of this unique ecosystem and help park managers protect the resources for the future.

The native cutthroat trout of Yellowstone Lake, a key species in the food web of the Yellowstone ecosystem, is both a top predator in the river ecosystem and prey for many terrestrial carnivores, including grizzly bears, white pelicans, bald eagles, and ospreys. The cutthroat trout provides an important link between aquatic and terrestrial productivity. The cutthroat trout fishery was a major early attraction of the park, and liberal fishing regulations led to the decline of fish stocks beginning in the 1920s. By the late 1960s, the popular sport fishery had virtually collapsed. A study of long-term measurements of rates of spawning and harvest left little doubt that overharvest had jeopardized the trout population. The NPS data base, coupled with an increased public awareness of the role of the fish in the park's ecosystems, led to the imposition of restrictive yet innovative regulations that have permitted the trout to increase and once again flourish. From Fishing Bridge in the park (which is now closed to fishing) visitors can witness a trout spawning run almost without parallel. Increases in the number of carnivores in Yellowstone National Park have been attributed in part to recovery of the trout. A fine sport fishery also has been restored and is once again an attraction for many park visitors.

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