Historical aspects of international movement of living aquatic species.

The use of exotic aquatic species to increase both the level of food production and the income generated by this production has been an established practice since the mid 19th century. At present, advances in husbandry have enabled large-scale movements of many different species over great distances. Despite a gradual fall in the volume of such movements since the 1960s, the practice still persists and continues to generate controversy in regard to the protection of native biological diversity, the spread of pests and disease, and socio-economic factors. The author presents the results of a recent international questionnaire on species introductions, distributed in an attempt to gain further insight into the uses and effects of introduced species. Information was received on 654 introductions of aquatic organisms, mostly fish. Aquaculture was the main reason for most introductions, followed by the creation of fisheries, the ornamental fish trade, research, biological control, accident, natural diffusion, and the provision of bait and forage. National governments were responsible for 40% of the introductions, with the private sector accounting for 18%, individuals another 15% and international organisations 7%, with the remaining 20% being of unknown source. The impact and benefits of many of the introductions reported were unclear. Most introductions (62%) probably did not result in the establishment of the exotic species in natural waters. Respondents reported that 63% of the introductions probably had no effect on th ecosystem: 25% of the impacts were judged positive, while for 58% the nature of the impact (positive or negative) was undetermined. Furthermore, 62% of the introductions probably had no effect on the socio-economic system: 40% of the impacts were beneficial, while in 55% of cases the respondents were undecided whether or not the impact was beneficial. The authors recommend that planning, regulation and monitoring of introductions of aquatic species be imposed through adherence to international and national codes of practice. This will help to maximise benefits from the use of exotic species in the future.