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Non-Native Fish Stocking What is a nonnative fish? What problems do nonnative fish species pose? How is nonnative fish species stocking a problem in this region? What can be done to fix or ameliorate the problem? A nonnative fish belongs to any fish species that did not originally spawn within a particular river, stream or lake. Typically, nonnative fish species are introduced by man into fishless bodies of water or those lacking an amount or species of desirable fish. Today, nonnative fish stocking is becoming a very controversial issue. The main problem with nonnative fish stocking is that these introduced fish may overtake native species of fish with perhaps a more aggressive or competitive nature or a better reproduction rate. In many states around the country introduced game fish are replacing more and more native species. Many biologists believe that this problem will ultimately lead to a decrease of fish diversity and an overall disruption of aquatic ecosystems. Fish introductions cannot only affect other species of fish but also amphibians, zooplankton, and benthic macroinvertebrates that happen to inhabit a particular body of water. Western Pennsylvania waterways may be the source and the destination for some non-native fish species and there lies a potential to disrupt ecosystems. Flathead catfish, including several young, have recently been caught below the Safe Harbor Dam on the lower Susquehanna River. Since 1997, flatheads have also been caught in the Delaware and Schuylkill rivers, and the Blue Marsh Reservoir, all in eastern Pennsylvania. The species is not native to eastern Pennsylvania, but it is a natural inhabitant of the Ohio River drainage, including the Allegheny and Monongahela rivers in Western Pennsylvania. Flatheads have been known to reach 100 pounds and are active predators. While it is not quite known how the flathead catfish became established in rivers in eastern Pennsylvania, there is great concern that its arrival could harm established fisheries there. Where the diets of flatheads have been studied, sunfish, other catfish and crayfish are principal prey items. Flatheads could disrupt native fisheries both by competing with native fish for food, and by eating native fish directly. In the Cape Fear River in North Carolina, where the flathead has also been introduced, researchers documented a severe decline in native fish populations within 15 years after flathead catfish became established there. Scientists found that after the flatheads had decimated populations of sunfish and other catfishes, they switched to feeding on shad. Unfortunately, the elimination of non-native species is not always possible, but where possible, the National Park Service is working to remove non-native species and reintroduce or restore native species to help reestablish natural aquatic ecosystems. Restoration is usually accomplished through electro fishing and the chemical treatment of stream sections above natural fish barriers (such as waterfalls) to remove all non-native fish, then native species are reintroduced from other surviving populations. The Water Resources Division is providing technical assistance for native fish restoration projects at several National Parks and will continue to do so over the next several decades. Fishermen can help restore native fish by releasing all native fish that they catch and keeping all non-native fish caught.
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