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The paddlefish has been listed as endangered in Missouri, and North and South <br />Dakota (Power and Ryckman 1998) and a fish of special concern to a number of states <br />(Williams et al. 1989). Sport fishing is allowed in all of these states, however many of <br />the fish caught are hatchery- reared fishes that are stocked. Causes of the decline in <br />paddlefish stocks have mainly been attributed to stream blockage by dams, habitat <br />alteration, and overfishing (Dillard et al. 1983). However, as in sturgeons, paddlefish <br />larvae drift downstream with flow after swim -up (Russell 1986) presumably to reach <br />more suitable habitats. In the present system reduced turbidity results in increased loss <br />due to predation, and especially if the larvae move into lacustrine areas that are <br />dominated by nonnative predators. Also, some fishes like common carp are presumed <br />to be in competition with paddlefish (Pflieger 1997). <br />DISCUSSION <br />Native fish communities can be affected by physical and biological changes in <br />habitat. Physical changes in habitat are usually obvious, but changes in the biological <br />component of habitat are not easily observed and are not as well understood. However, <br />in the last 20 years, much attention has been given to the unintended consequences <br />associated with fish introductions, and well- designed studies are producing alarming <br />results (e.g., see reviews by Moyle et al. 1986, Courtenay 1995, Tyus and Saunders <br />2000). <br />Adverse effects caused by fish introductions have been recognized by the <br />American Fisheries Society (AFS), the premier professional fisheries organization in <br />North America. While acknowledging the benefits that stocking has brought to <br />recreational and commercial fisheries, the AFS states that stocking has had "undesirable <br />effects on native species" and that stocking policy should be tempered by the need for <br />preserving biological diversity (Kohler and Courtenay 1986, Starnes et al. 1996). <br />Surprisingly, there is no comprehensive basinwide evaluation of the effects that <br />nonnative fishes have had on the native Missouri River fish fauna. However, all of the <br />mainstream reservoirs were constructed before passage of the Endangered Species Act <br />and before an environmental awareness of the world -wide biodiversity problem. When <br />the impoundments were filled, state fish management agencies were mostly concerned <br />with how to manage the huge new reservoirs for recreational sport fishing, and hatchery <br />production offered the potential for mitigating losses of desirable species such as <br />paddlefish. <br />Prior to 1950, fisheries programs in North America were devoted largely to <br />stocking gamefish. There were few ecologists, and "virtually all fisheries biologists were <br />fish culturists" (Wiley 1996). Although introductions of nonnative fishes were causing <br />considerable damage to native fish populations, little concern was registered in the <br />scientific literature. Only recently have federal and state fisheries agencies developed <br />management measures for nongame species. It is pertinent to note that little attention <br />27 <br />