Devin Bartley 1 and Christine V. Casal 2
Fishery Resources Division 1 Biodiversity and Genetic Resources Programme 2 ICLARM, Manila, Philippines


The following was presented by D. Bartley at Session 4 of the International Conference on Sustainable Use of Aquatic Biodiversity: Data, Tools and Collaboration 1 . ACP-EU Fisheries Research Initiative, 3 – 5 September, 1998, Lisbon Portugal. The article will also be distributed on CD ROM along with the other contributions from the meeting through the ACP-EU Fisheries Research Initiative. The assistance of ICLARM and the other organizers is gratefully acknowledged.

Risk assessment will require information from a number of sources on a number of areas such as the biology, ecology, and genetics of the alien species. The information will need to be readily available and understandable to those performing the risk assessment and to policy makers. Risk assessment must also include benefit assessment; an accurate accounting of the benefits derived from exotic species is essential. This note details information from two databases that stemmed from collaborative efforts of the European Community, ICLARM and FAO – FishBase (Froese and Pauley 1997) and DIAS (Database on Introductions of Aquatic Species) (Welcomme 1988; Bartley et al. 1997). The records in the databases came from questionnaires distributed internationally, from the literature, and from personal communications. The purpose of the paper is to examine what type of information is needed to make reasonable risk assessments and to use the databases to examine the impacts of alien species.


Impacts of introduced species will fall into two broad categories – i) ecological, which includes biological and genetic effects and ii) socio-economic (Table 1). However, these two categories are not independent and socio-economic changes brought about by alien species can in turn cause more ecological changes. Thus, a reduction in native species may be from direct interaction with an exotic species, or it may result from increased fishing pressure or changes in land use brought about by the presence of a newly established species. FishBase is a relational database that allows comparisons of multiple data-sets. Links of the Introductions module to the FAO Fishery Statistics (FAO 1998) module revealed that the contribution introduced fishes make to total fish production is about 17% (Figure 1).

Alien species 2 are receiving international attention in fora such as the Convention on Biological Diversity and the FAO Code of Conduct for Responsible Fisheries. While much of the recent attention has focused on the adverse impacts, not all alien species are bad. As in agriculture and ornamental horticulture, alien aquatic species have contributed to an improvement of the human condition in many areas. The production of the African cichlid tilapia is much higher in Asia (>700,000 mt in 1996) than in most areas of Africa (39,245 mt); introduced salmonids in Chile support a thriving aquaculture industry that is responsible for approximately 20% of the world’s farmed salmon. The practice of using species outside of their natural range to increase production or profitability can be expected to continue. The issue is not to ban alien species, or to abandon regulation of their movement, but rather, as stated in international codes of practice (ICES 1995) and the Convention on Biological Diversity, to assess the risks and benefits associated with their use and then, if appropriate, develop and implement a plan for their responsible use.

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Impacts may depend on the objective of the introduction. Analyses of the database reveals that aquaculture development was the most often cited reason for fish introductions, and that government organizations were responsible for more introductions than any other group. Table 2 presents information that most of the ecological effects of introduced species reported were negative; however, the socio-economic impacts were reported to be more often beneficial and there were more positive socio-economic benefits reported than negative ecological impacts.

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Table 3. Some popular conceptions regarding alien species





Most introductions fail

Where establishment was assessed, 65% of the introductions lead to established populations

Data from questionnaires, i.e. biased reporting

Moyle and Light 1996

Top carnivores are the most dangerous

Herbivores and carnivores were reported to cause negative impacts in >60% of the cases where impact was assessed, whereas the figure for omnivores was 81%

Small sample size of carnivore introductions

Moyle and Light 1996

r-selectd species 1 most likely to establish

Establishment success negatively correlated with max. size

Larger fish subsequently removed by fishing or other factors after establishment; larger fish take longer to establish noticeable populations

Pullin et al. 1997

Diverse environment hinders alien establishment Data-set cannot address the issue Moyle and Light 1996
Disturbed environment helps alien establishment Data-set cannot address the issue Moyle and Light 1996
Genome size inversely related to invasive ability DNA content and chromosome number were not related to establishment success Baker and Stebbins

1 species with high fecundity, short generation time, early age at maturity and usually small size.



Baker, H.G. and G.L. Stebbins. 1965. The Genetics of Colonizing Species. Academic Press.

Bartley, D.M., L. Garibaldi, and R.L. Welcomme. 1997. Introductions of aquatic organisms: a global perspective and database. Presented to the American Fisheries Society Symposium: Impacts, threats and control of introduced species in coastal waters, Monterey, California, 28 August, 1997.

FAO. 1998. FAO FishStat PC. Fishery Information, Data and Statistics Unit. Food and Agriculture Organization of the United Nations, Rome, Italy.

Froese. R. and D. Pauley, Editors. 1997. FishBase 97. Concepts, design, and data sources. ICLARM, Manila, Philippines. 256p.

ICES. 1995. ICES Code of Practice on the Introductions and Transfers of Marine Organisms. International Council for the Exploration of the Sea, Copenhagen, Denmark. 5p.

Moyle, P.B. and T.L. Light. 1996. Biological invasions of freshwater: empirical rules and assembly theory. Biological Conservation 78: 149 – 161.

Pullin, R.S.V., M.L. Palomares, C.V. Casal, M.M. Dey and D. Pauly. 1997. Environmental impacts of tilapia. ICLARM Contribution No. 1350.

Welcomme, R. L. 1988. International Introductions of Inland Aquatic Species. FAO Fisheries Technical Paper No. 294. Food and Agriculture Organization of the United Nations, Rome, Italy. 318pp.


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Introduced Atlantic salmon and rainbow trout have made Chile the world’s second leading producer of farmed salmon behind Norway; but the effect on native fauna is largely unknown.
Black bass introduced from North America along with local red breasted bream are sold along the roadside in Zimbabwe.

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