Chapter 8: Managing Undesired and Invading Fishes
Cindy S. Kolar, Walter R. Courtenay, Jr., and Leo G. Nico
Throughout much of history, humans have directly or indirectly facilitated the introduction of fishes and other aquatic organisms into areas where they had not previously existed, places outside their natural geographic distributions. These introductions have dramatically changed biological communities throughout the world. North America is no exception and the continent is now home to multiple species native to other parts of the world. In addition, many aquatic animals native to one or a few drainages and regions in North America have been transported by humans to other drainages and regions within the continent (Fuller et al. 1999). Through time, the many foreign introductions and intra-continental transplants, in conjunction with loss of native (often endemic) species, have resulted in aquatic faunas across North America that are increasingly homogenized and biologically less distinctive.
The motives behind aquatic organism introductions, the means by which they are introduced, and the ultimate outcomes of these introductions are many. A large proportion of introductions have been deliberate, usually a result of authorized stocking by governments or other institutions. However, there have also been a large number of illegal or otherwise unauthorized introductions. In addition, a wide variety of introductions have occurred that are considered accidental or unintended, a by-product of human activities (e.g., construction of a canal that allows dispersal of fish into new areas). In terms of motives, many fishes and certain other aquatic organisms have been introduced to establish food sources, create new fisheries, and restore depleted stocks (Fuller et al. 1999; Wydoski and Wiley 1999). In addition, a diverse array of nonnative and native fishes has been stocked for biological control of unwanted plants, invertebrates, and other fishes, as well as for conservation purposes. Introductions have also occurred as a result of unauthorized liberation of small fishes used as bait (i.e., bucket releases), releases of aquarium and water garden plants and pets, and escapes from aquaculture facilities. Aquatic species have also invaded new environments by way of water craft, usually by attaching to vessel hulls or by being carried in ship ballast water; others have invaded adjacent drainages by way of excavated canals or other artificial water channels (Courtenay 1993; Fuller et al. 1999).