Rocky Mountain National Park (Image Credit: National Park Service)
A long history of stocking
Fish stocking began in the area in 1886, before Rocky Mountain National Park was established. By 1968, more than 20 million fish had been introduced into waters that are now part of the national park. The National Park Service issued formal guidance on fish management in 1936, encouraging the use of native fish and discouraging the introduction of non-native species. By 1968, fish stocking had stopped.
Some of the introduced species were not naturally found in the region. That left park managers with a more complicated task: removing introduced fish from selected waterways so native species could recover. These trout historically occupied Colorado’s mountain waters, but their populations have been affected by competition and interactions with introduced fish. Fish were once introduced to make mountain waters more attractive to anglers.
Colorado stocked fish into mountain waters to create and expand opportunities for recreational fishing. The programme grew over the following decades. Hatcheries were established in Estes Park and Grand Lake, producing large numbers of fish for release into local waters. Non-native fish had become established across much of the park’s aquatic environment. The park’s fish-management philosophy eventually shifted from increasing fishing opportunities to protecting native ecosystems. However, ending stocking did not remove the non-native trout that were already established. Species such as brook trout remained in streams and could compete with native fish for food and habitat. The greenback cutthroat trout is one of the native species targeted by the restoration programme. Brook trout can compete with greenback cutthroat trout for resources, making the removal of non-native fish an important part of restoring native populations. The aim is not simply to reduce the number of fish in a stream. Instead, managers want to restore waterways where native trout can survive, reproduce and eventually expand their populations. The work represents a major reversal of a practice that lasted more than eight decades. The restoration will not undo the history of stocking overnight. But by removing non-native fish and restoring suitable habitat, the Poudre Headwaters Project is working toward a landscape where greenback cutthroat trout can once again occupy parts of their native range. The effort shows how conservation priorities can change over time: what was once considered beneficial for recreation can later require active restoration to protect the ecosystem.
Fish were even stocked in certain waters that had historically been fishless. Stocking in historically fishless waters was also prohibited. Today, managers are deliberately removing some of those same introduced species to give native trout a better chance of returning.