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Towards a New Partnership Edited b y Francesco di Castri Director of Research, C N R S Centre d'EcoZogie Fonctionelle et Evolutiue 1919 Route de Mende B.P. 5051 34033 Montpellier Cedex France and Talal Younès Executive Director Internafional Unioiz of Biological Sciences 51, Boulevard de Moiztmorency 75016 Paris ~ CAB INTERNATIONAL 3 ,< 1 in nssociation with the International Union of Biological Sciences Freshwater ecosystems occupying less than 1%of the surface of the Earth, are inhabited by more than 25% of the vertebrates. Fish which consitute the bulk of this fauna, are currently exposed to the consequences of major impacts resulting from anthropogenic activities: management of water systems for hydropower or agriculture purposes, pollutions, overexploitation of natural resources including living resources, introduction of alien species. The result is that a great number of endemic fish species are presently endangered. Among major threats, the question of the introduction of alien fish species became a matter of debate among freshwater ecologists and managers during the last decades. The main goals of voluntary introductions, most usually decided by fishery officers, were initially to improve sport fisheries, artisanal fisheries and aquaculture, or to develop biological control of aquatic diseases, insects and plants. More recently, transfers of ornamental fish for the aquarium trade have also sharply increased, as well as 'accidental' introductions of these species into freshwater ecosystems. The future promises a continuing spread of exotic species, and managers of aquatic ecosystems will be confronted increasingly with a shifting mix of native and non-native species. However, although the introduction of species has been encouraged all around the world both by managers and scientists for centuries, many ecologists consider it today to be like Pandora's box. The consequence is that any planned introduction is viewed as a potential ecological catastrophe, and that both its ecological and economical potential values are not objectively considered. Are introductions of fish speciesta way to encourage in order to improve fisheries, or a major threat to freshwater biodiversity, or a game of chance as suggested by number of ecologists? Whereas many scientists, more or less O 1996 CAB INTERNATIONAL. Biodiversity, Science and Development: Towards a New Partnership (eds F. di Castri and T. Younès) Introduction of Fish Species in Freshwafers 447 intuitively, claim that the introduction of exotic species is risky, there are also examples of assumed success when the goal was to improve artisanal fisheries. We need therefore a very careful assessment of past experiences in order to develop general guidelines and policies about fish introductions which are scientifically based. Purposes of Introductions The first attempts to introduce true exotic species are not exactly known, but the modern era of introductions started during the second half of the nineteenth century. In Europe, these introductions of exotics involved mainly North American species: salmonids (the brook trout was introduced to the United Kingdom in 1869), catfishes (Icfalurus spp.) and centrarchids. There are different motives for performing introductions (Welcomme, 1988; Moreau efal., 1988). During the niheteenth century and until about World War II, fish introductions were largely an outgrowth of colonialism and nostalgia by settlers in their newly adopted homelands for the familiar species and surroundings left behind (Welcomme, 1984). Acclimatization societies proliferated for instance in New Zealand in the late 1800s to a point that of the 46 fish species now found, 20 are exotic (McDowell, 1990). Several species, usually salmonids o r top predators, have been introduced in different parts of the world as sport fish. The most spectacular example is that of the brown trout (Salmo f r u f f a ) ,native from Europe and now occurring worldwide (Baglinière and Maisse, 1991). More than a hundred fish species have been introduced for fish culture, but less than ten now have a worldwide distribution. The common carp (Cyprinus Carpio) and the herbivorous carp (Cfenopharyngodon i d d a ) , now occur in many temperate countries. In the intertropical area, several species of tilapiines (family Cichlidae) native to Africa, such as Oreochromis nilotirus and to a lesser extent Oreochromis mossambicus, make up the bulk of the fish culture production in Southeast Asia. They have also been introduced in South America, as well as Australia. One of the purposes of fish introductions has been the control of the aquatic vegetation. The grass carp, Cfenopharyngodon idella, has been successfully used in many countries for the control of aquatic macrophytes. Tilapia rendalli as well has been introduced into Sudanese irrigation channels and some artificial lakes of Shaba to control aquatic vegetation (Philippart and Ruwet, 1982). Fish introduction has also been suggested for disease control. That is the case for instance for Asfatoreochromis alluaudi, a 'mollusc crushing' cichlid under threat of extinction in East Africa, whose introduction to Cameroon has been proposed for control of snails involved in schistosomiasis transmission (Slootweg, 1989). The mosquitofish (Gambusia affinis) native from southern United States, and guppy (Poecilia reticulafa)native from north-eastern South America, were introduced worldwide after the World War II to control larvae of mosquito vectors of malaria. A current major cause of introduction is the trade of ornamental fish. For ' ' 448 C. Lévêque the past few decades, several thousands of small, usually tropical species, have been disseminated around the world by the aquarium fish trade. A famous and ancient example is the popular gold fish, Carassius aurafus aurutus, which has achieved a wide distribution for rearing in ornamental ponds. Most of these fish are rarely recorded as introduced, but can accidentally escape or be introduced in natural water bodies. It is generally assumed that they cannot survive in temperate climates, although populations may survive in artificial warm waters. Many introductions of alien fish into natural environments appear to have been more or less accidental, and occurred during the deliberate introduction of another species, because of confusions in identification. That is the case, for instance, with batches of stock-fish contaminated with unnoticed juveniles of another species. What Have We Learned about the Consequences of Fish Introductions on Biodiversity and the Aquatic Environment? From the different experiences in fish introduction, some general reflections should be derived. The introduction of large predators can be almost catastrophic in complex fish communities which evolved in tropical lakes with considerable specialization in feeding and reproduction. A well-documented example was the accidental introduction of the cichlid piscivore, Cichla ocellaris, to Gatun lake, Panama, around 1967 (Zaret and Paine, 1973). In less than five years, the introduced species which has voracious predatory habits, led to the elimination of six of the eight common fish and decimated a seventh. The large predator Lates niloficus was introduced into Lake Victoria during the 1950s and early 1960s to boost fisheries. During the first 25 year after its introduction, catches of the Nile perch were insignificant. However, in the early 1980s an explosive increase in the catches took place and simultaneously stocks of endemic cichlids have been decimated (OgutuOhwayo, 1990).It can be assumed that the establishment of the Nile perch was initially supported by the large quantities of native haplochromines which were their main prey. As a result, about two-thirds of the flock of 300 haplochromine cichlid species have disappeared or are threatened with extinction (Witte ef al., 1992). One of the major problems in fish species introductions, is their irreversibility, at least on the scale of a human's lifetime, Once introduced and established, it is impossible, given current technology, to eradicate a fish species from a large natural water body. Most information about the effects of introduced species on native fish is often anecdotal and fragmentary, not only because so little is known about native fish, but because the effects of the introduced fish have been overshadowed by the effects of environmental changes which have occurred simultaneous1.y. For instance, although it has been claimed that the introduced Introducfion of Fish Species in Freshwaters Nile perch was responsible for the decline of the native cichlids, the impact of human activities in the vicinity of Lake Victoria could also be involved. The lake has experienced profound changes over the last 30 years (Witte et a2, , 1992). Eutrophication, as well as the introduction of new fishing techniques (trawling) certainly contributed significantly to the decline of the Haplochromis fauna. It has been shown that the haplochromine stock was already affected by fisheries before the establishment of Lafes (Ogutu-Ohwayo, 1990). In newly created habitats (geologically young lakes, reservoirs) only a few species of riverine fish are adapted to take advantage of the deep o r open waters and to occupy adequately the newly created niches. The creation of reservoirs provides the habitat but not the preadapted inhabitants (Fernando, 1991). From the vast number of tropical freshwater fish only Cichlidae and Clupeidae, and to a limited extent Cyprinidae, have proved to be preadapted to colonize lacustrine habitats and to increase the total fish yield substantially. However, it seems reasonable to limit their introduction into reservoirs or natural lakes of recent origin, while introduction into ancient lakes must be very carefully considered (Fernando and Holcik, 1982). In aquatic ecosystems containing a very depauperate indigenous freshwater fauna as a result of historical and biogeographical events, the introduction of appropriate fish species that would occupy presently vacant or underutilized niches, could significantly improve the fishery. For example, O. mossambicus introduced in the Sepik River (Papua New Guinea) makes up about 50% of the present catch in inland fisheries (Coates, 1987). It should also be recalled that Ireland's current freshwater fish fauna consists of 20 species, whereas after the last glaciation, the fish fauna probably consisted of only about eight anadromous species. At least seven species were introduced into Ireland within the last 400 years or so (Fitzmaurice, 1984). Introductions for the purposes of fish conservation is a new option, for conservationists. A captive breeding programme may be considered as a way to save taxa threatened with extinction in the wild and to provide propagules for the repopulation of natural habitats. However, the restocking of captive bred fish to their native habitats is not always realistic and cannot necessarily be considered as the ultimate goal of breeding programmes. Indeed, reintroduction should take place only in localities where the original causes of extinction have been removed, and where habitat requirements of the species are satisfied. In the case of Lake Victoria for instance, reintroduction would be futile as long as the Lates threat persists, and the eutrophication of the lake is not controlled. To save endangered fish species, conservationists, therefore suggested introducing them into other ecologically suitable habitats, similar or identical to the original one, in order to initiate new safety net populations in appropriate waters. In other words, fish introductions may receive particuIar attention in that case, as a way of saving endemic species from extinction, providing similar habitats may be found for these species. 450 C. Lkvêqtie Conclusions Are introductions a game of chance? Most scientists more or less agree that the introduction of exotic species is risky, and many examples have been given that provide evidence of the potential threats. But there are also examples of apparent success which demonstrate the need for very careful impact assessments prior to any introduction. The assessment of the impact of fish introduced in Asia (De Silva, 1989), is that this continent has suffered few losses of native species to introductions. The need for better communication between the scientific community and managers or administrators has been raised many times (Balon and Bruton, 1986) as well as the need for establishing formal protocols for the evaluation of risks, both for indigenous species and for ecological balance, prior to any introduction. Balon and Bruton (1986) also clearly pointed out the difficulties of such procedures: are decision-makers willing to accept advice which does not conform to their schemes? Do scientists have sufficient knowledge to give clear and unequivocal advice? In fact, biologists have a limited ability to predict the outcome of introductions because of an inability to answer some fundamental biological questions. Applied research programmes should be devised urgently to improve the documentation of the consequences of fish introductions, starting with the more common species. Both field and controlled experiments should be conducted using the already available information to assess direct and indirect effects of introductions. But decision-makers should also realize that the lack of regulation and control makes it difficult nowadays to avoid possible major ecological threats in the near future. References Allan, J.D. and Flecker, AS. (1993) Biodiversity conservation in runnning waters. Bioscience 43, 32-43. Baglinière, J.L. and Maisse, G. (1991) La Truife:Biologie et .Écolegie. INRA Editions, Paris. Balon, E.K. and Bruton, M.N. (1986) Introduction of alien species or why scientific advice is not heeded. Environmental Biology of Fishes 16, 225-230. Coates, D. (1987) Consideration on fish introductions into the Sepik River, Papua New Guinea. Aquaculture and Fisheries Management 18, 231-241. De Silva, S.S. (1989) Exotic aquatic organisms in Asia. Special Publication of the Asian Fisheries Society 3, 156 pp. Fernando, C.H. (1991) Impacts of fish introductions in tropical Asia and America. Canadian Journal of Fisheries and Aquatic Science 48 (Suppl. I ) ,24-32. Fernando, C.H. and Holcik, J. (1982) The nature of fish community: a factor influencing the fishery potential and yields of tropical lakes and reservoirs. Hydrobiologia 97, 127-140. Fitzmaurice, P. (1984) The effects of freshwater fish introductions into Ireland EIFAC Technical paper (suppl. vol) 449-457. Introduction of Fish Species in Freshwafers McDowall, R.M. (1990) New Zealand Freshwater Fishes: a Natural History and Guide. Heinnemann, Auckland, New Zealand. Moreau, J., Arrignon, J, and Jubb, R.A. (1988) Les introductions d'espèces étrangères dans les eaux continentales africaines. In: Lévêque, C., Bruton, M.N. and Ssentongo, G.W. (eds) Biology and Ecology of African Freshwater Fishes. ORSTOM, Paris, pp. 395-425. Ogutu-Ohwayo, R. (1990) The reduction in fish species diversity in lakes Victoria and Kyoga (East Africa) following human exploitation and introduction of non-native fishes. Journal of Fish Biology 37, 207-208. Philippart, J.C. and Ruwet, J.C. (1982) Ecology and distribution of Tilapias. In: Pullin, R.V.S. and Lowe-McConnell, R. (eds) The Biology and Culture of Tilapias. ICLARM Conference Proceedings 7. ICLARM, Manila, Philippines, pp. 15-59. Slooteweg, R. (1989) Proposed introduction of Astatoreochrotnis alluaudi, an East African mollusc-crushing cichlid, as a means of snail control. Annales du Musée Royal d'Afrique Centrale, Sciences Zoologiques 257, 61-64. Welcomme, R.L. (1984) International transfers of inland fish species. In: Courtenay, W.R. and Stauffer, J.R. (eds) Distribufion, Biology, and Management o f Exotic Fishes. The Johns Hopkins University Press, Baltimore, Maryland, pp. 22-40. Welcomme, R.L. (1988) International introductions of inland aquatic species. FAO Fisheries Technical Paper 294, Rome, 318 pp. Witte, F., Goldschmidt, T., Wanink, J., van Oijen, M., Goudswaard, K., Witte-Maas, E. and Bouton, N.(1992) The destruction of an endemic species flock: quantitative data on the decline of the haplochromine cichlids of Lake Victoria. Environmental Biology of Fishes 34, 1-28. Zaret, T.M. and Paine, R.T. (1973) Species introductions in a tropical lake. Science 182, 449-455.