The Repercussions of Illegal Stocking by Anglers

Unauthorized fish introductions are a frustrating problem for fishery managers, particularly when the introduced species conflicts with management goals and jeopardizes fishery sustainability.  The problem can become more serious when the practice interferes with efforts to conserve or recover sensitive species. In some circumstances illegal introductions have even altered contaminant bioaccumulation and potential exposure of anglers and their families to environmental toxins.  Illegal introduction of nonnative sport fish is a common practice in the Upper Colorado River Basin (UCRB), with more than 50 populations of cool- and warmwater species established by this means.  These populations have increased sport fishery management costs by necessitating the stocking of larger trout to avoid predation by introduced piscivores, and have the potential to degrade kokanee salmon fisheries valued at millions of dollars.  Dispersal of introduced piscivores into native fish habitat is a primary factor limiting recovery of endangered fishes in the UCRB with a similar level of economic impact.  When nonnative piscivores were introduced into some Colorado reservoirs historically managed for panfish and salmonids, availability of the latter decreased while the mercury concentration of the former increased beyond levels safe for human consumption. Apparently, some people are unaware that their efforts to establish new sport fish populations can have significant effects contrary to their own goals and personal well-being.  Because most introductions are difficult to remedy, fishery professionals should strive to educate anglers that illegal stocking can be counterproductive, sometimes with significant economic and human health implications.