Dispersal of Exotic Species from Aquaculture Sources, with Emphasis on Freshwater Fishes

CHAPTER 1 Movement and Dispersal of Exotic Species DISPERSAL OF LIVING ORGANISMS INTO AQUATIC ECOSYSTEMS Edited by Aaron Rosenfield National Marine Fisheries Service National Oceanic and Armosoheric Adminstration Roger Mann Virginia Institute of Marine Science /990 Dispersal of Exotic Species from Aquaculture Sources, with Emphasis on Freshwater Fishes WALTER R. COURTENAY, JR. JAMES D. WILLIAMS Abstract: Since the beginning of translocations of aquatic species beyond their historical ranges, there have been escapes and releases from culture facilities. Most escapes have resulted from carelessness in construction and operation of these facilities. In some instances, there appear to have been deliberate releases of stocks. To date, pet industry culture facilities have been the source of more introductions in the United States than has the culture of fishes for food or other purposes. Of the 46 established exotic fishes in the waters of the contiguous U.S., 22 are the result of aquaculture activities. Future development of aquaculture of food resources, however, promises to become a major source of introductions unless precautions are taken early. Recognition that introduced exotic aquatic species have been, or have the potential to be, detrimental to native species and ecosystems, and can create negative economic impacts, is reason for concern and caution. Guidelines for safety in importation and culture practices must be developed that will enhance both the future of aquaculture and protec- tion of irreplaceable native natural resources. Introduction Aquaculture is a relatively new term for a very old practice — the culture of aquatic organisms. Bardach et al. (1972) stated that pond culture of carps is known from the fifth century B.C. in China. In Europe, culture of common carp, Cyprinus carpio Linnaeus, apparently began during the time of the Roman Em- pire as part of the medieval monastic pond fish culture practice (Balon 1974; Welcomme 1984, 1988). The source of wild common carp for use in monastic fish culture is presumed to have been the Danube, where this species is native. From there, this fish 49 50 / Dispersal of Living Organisms was distributed widely throughout Europe, with subsequent escapes into natural waters where it became established as repro- ducing populations. Primarily because of its long history as a popular aquaculture species in Europe, emigrants to other continents were in large part responsible for movement of common carp into continents where the species was not native. These transfers began on a massive scale in the latter half of the 1800s. Wekomme (1988) noted that the common carp now has a nearly global distribution because of these transfers, subsequent escapes from culture facilities, and deliberate introductions into natural waters. As an introduced exotic (of foreign origin) species, it ranks third in international transfers, behind Mozambique tilapia, Oreochromis mossambicus (Peters) and rainbow trout, Oncorhynchus mykiss (Walbaum), and has been successfully released into 59 countries (Welcomme 1988). Common carp provides an interesting contrast in opinions on its impact. It is a major species in inland aquaculture. Pullin (1986) noted that approximately 250,000 metric tons of carp are produced annually by aquaculture. In several countries, it is a subject of capture fisheries. Common carp has also been accused of being a detrimental species in many areas where it has found its way or was released into open waters, due to its habit of up- rooting aquatic vegetation with subsequent increases in turbidity and lowering of oxygen levels. It is also known to feed on eggs of native fishes, including those of endangered and threatened species. Thus, it is a species that is praised in some aquaculture circles and simultaneously cursed by environmentally oriented groups (Cooper 1987). Prior to 1900, international transfers of fishes for aquaculture purposes largely involved salmonids intended for introduction or repeated stockings as sport species, and some limited food production. Movements of common carp to North America began in the 1830s (DeKay 1842) and peaked in the last quarter of the 1800s (Smiley 1886; Courtenay et al. 1984; Crossman 1984; Contreras and Escalante 1984); southern Africa experienced a simi- Dispersal of Freshwater Fishes / 51 lar history with this species (de Moor and Bruton 1988). Wekonune (1988) reported that common carp reached its great- est popularity in international transfers between 1910 and 1940, being replaced by tilapias from 1950 to 1979 and Chinese carps from 1960 to 1980 "as preferred species." Present international interest in exotic species for aquaculture purposes includes a number of crustaceans, while in the United States tilapias and Chi- nese carps are of growing popularity among aquaculturists. Similar opinions exist in relation to the second most widely transferred aquaculture fish, Mozambique tilapia, now found in 66 nations (Wekomme 1988). Its present distribution is almost pan-tropical. The first escape into waters where it is exotic may have been during the 1930s in Java, where it is thought to have been an aquarium fish release. This species is of great and in- creasing importance in modern aquaculture as a food fish. It has also been promoted for biological control purposes but its effec- tiveness is questionable. Like common carp, it is typically cultured in ponds, but in some nations it has been widely dissemi- nated into natural waters. In several nations, the Mozambique tilapia is considered as a pest species due to its high fecundity, nature of producing stunted stocks, and its ability to displace native fishes (Bardach et al. 1972; Ling 1977; Shelton and Stnitherman 1984). Aquatulture and agriculture provide some important paral- lels and contrasts. The early development of agriculture in the Western Hemisphere was characterized by importations of exotic plant and animal species, just as there is now great interest in the use of exotic species in the developing aquaculture industry. One of the major contrasts is that agriculture involves mostly plants and animals that are so far removed genetically from their wild ancestors that they require care and husbandry to survive, with few persisting in a feral state. The few able to persist on their own include feral goats, pigs, donkeys, and horses, and these have created environmental management problems in several areas. Species employed in aquaculture are mostly feral stocks being reared artificially, and most have the capability to return to a fe- 52/ Dispersal of Living Organisms ral state if released, within or outside their native ranges of distribution. A second contrast is that the technology of agriculture far outpaces that of aquaculture, largely due to the longer history of the former and its predominant importance to mankind. In such areas as nutrition, disease control, genetics, and husbandry, aquaculture has a lot of experience yet to be obtained and utilized. In nearly every instance where an exotic aquatic species has been the subject of culture, escape into open waters has occurred. Shelton and Smitherman (1984) noted, "For whatever purpose an exotic fish is used, escape is virtually inevitable; thus, this even- tuality should be considered." Welcomme (1988) added, "Species originally introduced for aquaculture eventually escape from the confinement of their ponds often but not always to colonize natural waters. Therefore any introduction made for aquaculture must be thought of as a potential addition to the wild fauna in the receiving country." Moreover, many introduced exotic species have had negative impacts on native organisms, habitat, and re- gional and national economies (Elton 1958; Laycock 1966; Courtenay 1979, in press a). It is these concerns, escape and impacts, that are the focus of this contribution. Currently there are 46 species of exotic fishes established in open waters of the contiguous U.S. (Table 1). Additionally, an- other 14 species were established, but some were purposefully eradicated and others failed to survive, probably due to cold win- ter temperatures (Table 2). Fifty-three more, identified to species, and 7, identified only to genus (doubtless representing far more than 7 species), have been collected or reported from open waters; none is known to be established (Table 2). The majority of these introduced exotic fishes escaped from ornamental aquarium fish culture facilities or were released by aquarists (Courtenay et al. 1984, 1986b; Courtenay and Stauffer 1990). An unquantified number of alien aquatic invertebrate and plant species is also present, with several, particularly plants, having achieved status as major pests. Nearly all the introduced exotic fishes, a few in- vertebrates, and several aquatic plants were cultured at some time in the United States prior to their escape or intentional dissemi- Dispersal of Freshwater Fishes / 53 nation into open waters. Bardach et al. (1972) defined aquaculture as "the growing of aquatic organisms under controlled conditions." Controlled conditions obviously does not mean "escape-proof." This definition is broad and could encompass activities from outdoor farming of aquatic organisms to maintaining aquarium species indoors. In- deed, it also encompasses the culture of species intended for stock- ing or introduction into natural waters. As used here, aquaculture will be confined to the culturing of aquatic organisms for food, sport, biological control, and aquarium purposes. Species from Aquaculture for Food Resources In many protein-deficient nations, governmental agencies re- gard the widespread introduction of exotic species to open waters as a form of aquaculture (Contreras and Escalante 1984; Erdman 1984; Maciolek 1984; Courtenay and Kohler 1986; Courtenay, in press a). Their philosophy appears to be that they have made these new resources available to the public. The as- sumption is that capture fisheries by individuals or commercial fishermen will solve a continuing and perhaps growing nutrition problem. While aquaculturists in the U.S. may disagree with or perhaps find humor in such an unfortunate approach, our own history includes similarities.

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