Fish Stocking

Over the last century many lakes and streams have been artificially stocked with popular non-native fish to provide sport for recreational fishermen. Hatchery stock have been introduced into waters with existing fish populations and also into naturally fishless lakes, delivered to remote areas originally by packstock and now by helicopter. Today fish stocking is also employed in recovery efforts aimed either at trying to restore native species to their historical range, or introducing a threatened but non-native species into viable habitat.

There are many well-documented impacts associated with fish stocking, and the effects on aquatic ecosystems has been profound. Introducing non-native fish has caused many native fish populations to plummet due to predation, competition, and hybridization. Fish stocking has caused many indigenous fish and amphibian species to qualify for listing as threatened or endangered. Stocking fish into naturally fishless waters such as many high mountain lakes can have major adverse impacts on invertebrates and amphibians due to predation. An example is the now-endangered Mountain Yellow-legged Frog in the High Sierra.

Poisons, such as rotenone and antimycin, are often used in conjunction with fish stocking projects. Engineered to basically starve fish of oxygen, these poisons are used to terminate existing populations of fish before the introduction (or re-introduction) of a different fish species. Both poisons have known adverse effects on aquatic biota, killing not only the targeted fish, but also much of the amphibian and invertebrate populations. Proponents of fish poisoning claim that invertebrate populations quickly return to the area, but scientific research indicates that the new invertebrate populations are not the same species that occupied an area prior to poisoning, due to a variety of complex factors. The impacts of these changes in an ecosystem remain largely unknown.

There are many documented instances where the poisons have traveled many miles downstream beyond the intended application site. Risks posed to drinking water obtained from private wells is uncertain. Although rotenone and antimycin decompose quickly and thereby limit bio-accumulation in birds and mammals that may eat the dead fish, the use instructions specifically require that birds and animals be prevented from drinking the poisoned water for 48 hours. This is impossible to achieve on wilderness lakes and streams, so risks to wildlife are uncertain.

It is extremely likely that there are many other unknown hazards associated with these poisons since their full effects on human health and aquatic ecosystems remains largely unstudied. For this reason some states such as California have banned antimycin, and the Environmental Protection Agency is considering withdrawing it from use nationwide until its environmental impacts are more thoroughly understood.

Fish Stocking and Wilderness

Poisoning lakes and streams and fish stocking represent intentional human interference in natural processes. The Wilderness Act clearly intended that humans would interact differently with wilderness than we do with any other landscape, as indicated in the statutory definition of wilderness found in Section 2(c) of the Wilderness Act:

"A wilderness, in contrast with those areas where man and his own works dominate the landscape, is hereby recognized as an area where the earth and community of life are untrammeled by man, where man himself is a visitor who does not remain."

Remaining in contrast to human civilization and untrammeled by intentional human manipulations are key conditions that define statutory wilderness. The Wilderness Act does not require managers to somehow restore wilderness to pre-Columbian conditions. The word “restore” does not appear in the Act. Many human actions that pre-date wilderness designation have shaped current conditions of the NWPS — prior fishstocking, fire suppression, commercial trapping, livestock grazing, homesteading, farming, prospecting, etc. However, once designated as wilderness, the Act intends that natural processes be allowed to operate unrestrained and untrammeled by intentional human interference from that point forward.

“Untrammeled. A key descriptor of wilderness in the Wilderness Act, untrammeled refers to the freedom of a landscape from the human attempt to intervene, alter, control, or manipulate natural conditions or processes to provide particular benefits.” — FWS Draft Wilderness Stewardship Policy, 2001, Federal Register

Natural processes in wilderness should not be manipulated to enhance certain recreational benefits such as sport fishing. Expansion of recreational fishing is the most common goal behind most poisoning and stocking proposals. This goal is sometimes masked as an effort to prevent further decline of a native fish species. One example is a proposal to use helicopters and motorboats to poison several lakes within the Bob Marshall Wilderness Complex to remove non-native trout, and replace them with Westslope Cutthroat Trout that are native to the region. The problem is that these lakes were naturally fishless prior to artificial stocking, and have never been home to Westslope Cutthroat, although the species is indigenous to streams on the other side of the Continental Divide.
Whether or not to poison waters in wilderness to remove non-native fish that were previously introduced is a complex question. However, the Wilderness Act’s emphasis on leaving wilderness untrammeled makes it clear that it is always wrong to re-stock the waters with other non-indigenous fish.

The presence of indigenous species is a valuable component of an area’s wilderness character. For this reason, some form of manipulation may be justified in order to prevent the loss of a threatened or endangered species. The impact of previously stocked non-native fish on the ecosystem should be carefully assessed. If their presence is placing indigenous species in serious jeopardy, then removal of the non-native fish may be justified, but this may not always be the case.

Although prior fish stocking may have modified the ecosystem to some extent, sometimes the system may be stable and healthy, as species adjusted over a long span of time. In such a situation trammeling wilderness is probably not justified if the goal is primarily an attempt to return to conditions to those that existed at some prior snapshot in time. Natural processes including climate changes are constantly shaping and changing landscapes over time, so prior modifications are not automatically a justification for manipulating wilderness now.

When prior fish stocking has resulted in placing indigenous species at serious risk, then removal of the non-native fish may be the necessary minimum requirement to protect the area’s wilderness character.

However, poisons and motorized equipment should not be the first method of choice. Rigorous analysis of less systemic alternatives should be done, such as matting of spawning beds to reduce reproduction of the non-native fish, ending all sport fish stocking in the watershed to allow indigenous species to gradually replace the non-natives over time, relaxing angling rules to allow larger daily limits on the non-native fish, and electrofishing to stun the fish and net the non-natives as they float to the surface.