It's important to consider carefully whether fish stocking is necessary and plan out all the steps of the implementation, because once the fish are stocked, it's nearly impossible to reverse the process. To further compound the difficulty of the planning process, however, you have to consider that success of a fish stocking will mean different things to different people. To a recreational fisherman, having a record-breaking fish at the end of the line is a victory, while an environmentalist may bemoan the impact that record-breaking fish had on the existing populations. And sometimes everything dies no matter what you do.
One impact to the existing populations relates to genetics. Say we added one species of trout to waters that already had another kind of trout. If the two different types of trout were to mate, the genetic purity of each line would be lost, and there would be less genetic diversity in the water. In 1959, stocking was banned at Yellowstone National Park for this reason; the cross-breeding was erasing the uniqueness of existing fish populations [source: Wuerthner].
But beyond a seeming inability to fend off the amorous advances of the stocked fish, the native fish face other struggles as well. Stocked fish consume resources that the native fish need as well. But to add insult to injury, stocked fish may often end up dying, so not only do they eat and run, the native fish are left with nothing and eventually die as well.
The native fish aren't the only ones dying -- fish stocking can have an impact on the greater ecosystem as well. For example, when gulls in the Great Lakes area were studied after a fish stocking, they were found to have consumed more terrestrial food items, including garbage. This is likely because the stocked fish preyed on the native fish that otherwise would have been the birds' meals [source: Ecological Society of America]. One study indicates that stocked fish in the Pacific Northwest spread a disease that resulted in a 15 percent increase in amphibian embryo death [source: Meadows].
For these reasons, not everyone is on board with fish stocking. While fishermen enjoy an easy hunt, some say that there are plenty of fish available naturally for an enterprising fisherman without the government and fisheries getting involved [source: Ingold]. Indeed, if stocking fish ends up killing off the native populations, then the stocking ultimately may ruin the practice altogether. Fishing restrictions are sometimes considered as an alternative to fish stocking.
But is there an alternative to fish stocking for a guy who loves his rod and reel? After banning fish stocking, Yellowstone has had great success with a catch-and-release method. Park officials have found that native fish are caught and released approximately 10 times per season; the stocked fish were only caught once and were generally smaller compared to the natives [source: Spooner]. Some other alternatives to stocked fish rely on the principle, "If you build it, they will come." These methods involve making waters more naturally attractive to fish by promoting aquatic plant growth (thus providing more food) and creating shallow, shaded areas for spawning (thus providing a love nest for the fish).
For more on fishery management, see the links on the next page.