6. Following the recommendation of the eleventh session of EIFAC, a Symposium on Stock Enhancement in the Management of Freshwater Fisheries was organized and held in the period immediately preceeding the twelfth session of EIFAC, from 31 May to 2 June 1982. The Symposium was chaired by Prof. T. Backiel. A full report of the meeting will be prepared and published in the EIFAC series and will consist of the summaries of the various sessions and of the discussions and general conclusions.
7. It became clear during the Symposium that, although practically all countries practice stocking with a great number of species, there are very few evaluations and the assessment of success or failure is often controversial. Examples of successful stocking include eel, in which stocking has been accepted as necessary and profitable in a number of European countries. On the other hand, stocking with pike often did not lead to any community enhancement. The review of stocking with salmonids clarified many, but not all, aspects of current practice.
8. Stocking with coregonids is similarly widely practised in northern European countries and in Canada, but again the results are quite controversial. It was emphasized for instance that coregonids exhibit great taxonomic variability which makes evaluation of stocking more difficult than with other species. Furthermore, one cannot exclude consideration of introductions of exotic coregonids when discussing stocking with the native species, as examples were given of possible hybridization yielding new genetic stocks.
9. With respect to cyprinids, the evidence is vague and far from convincing and much work has to be done before any practical conclusions can be reached.
10. Several technical aspects were dealt with during the Symposium. One which was discussed was the relationship between the size of fish stocked and the results of such stockings. Evidence was produced for both salmonids and coregonids that stocking with older fish is usually more successful than stocking with 0+ fish. The time of stocking was also felt to be significant, better results being achieved with spring stockings. The importance of stress during the transportation of fish and possibilities of avoiding it by means of tranquilizers raised some controversy.
11. In view of the general paucity of information on the success or failure of current practice in most species, the Symposium felt that further efforts were needed by EIFAC to clarify those problems.
12. During the Symposium it was made clear that there were conflicting views on the success and failure of introductions. Many salmonid introductions have been less than successful and certain introductions with other species, for instance the alewife in the USA, could be considered disasters. A few success stories were also cited such as the transplant of the barbel into the River Severn or the introductions of the signal crayfish into Finland, which were well prepared for by prior study. This diversity of opinion was particularly obvious when considering species such as the pikeperch, thought of as a valuable addition to the fauna by Denmark and a plague for the fishermen of East Anglia, UK.
13. Attention was drawn to the fact that unauthorized stocking was resulting from the introduction by anglers of exotic species to countries for use as bait, in some cases unwittingly and in other cases intentionally to enhance their angling possibilities and concern was expressed at this practice while recognizing the difficulty in controlling it.
14. Much of the diversity of viewpoint clearly arises from differential response of introduced fish under different environmental conditions and different native fish community structures. However, it is also obvious that the judgement of success or failure of an introduction depends very much on social attitudes. There are the extreme views of the conservationists who would prohibit all interference with the status quo, although such transfers may occur naturally when one river captures another, or there is at the other extreme the view that anything goes. In between the two there has to be a careful tradeoff between the quality required by one block of users against the quantity required by another. This has emerged particularly well in the case of pikeperch introductions into UK, where education of the angler may well transform what is now viewed as a bad introduction into a useful resource. Such trade-offs become especially important in international river systems where solutions greeted with joy in one country may be viewed with a jaundiced eye by a country further downstream.
15. It is also clear that disasters do occur which please no group of users. These are usually one of two types.
16. Firstly, by effects of the species itself either, in the case of a predator, by elimination of valued local species, or in the case of forage fish, by stunting and population explosion: of the two, the latter seems more common on a world scale. Secondly, by incidental effects, such as the introduction of a disease organism or the alteration of the environment by elimination of water weeds, etc.
17. One of the principal conclusions of the Symposium requiring action by EIFAC was that, due to the varied and often deleterious effects to native fish communities of introductions of exotic species of fish, there was a need for the establishment of procedures whereby such introductions could be submitted to more rigorous and scientific evaluation before they are carried out.
18. The other main conclusion was that more work on stocking and assessment of its results is necessary and requires a scientific approach and evaluation.
19. Therefore, the Symposium recommended to EIFAC that it adopt a code of practice to reduce the risk of adverse effects arising from the introduction or transfer of inland fish species. This recommendation is further discussed under paragraph 23.
20. It further recommended to EIFAC that it set up a working party on stock enhancement with the following terms of reference:
to review and recommend to EIFAC a code of practice for the regulation of the introduction of exotic species and procedures for its implementation, and
to review the present status of stocking and to elaborate guidelines for stocking with various species groups forming part of established fishery management practices.
21. The Symposium also recommended that selected papers made available to the meeting should be edited and published as an annex to the proceedings of the meeting.
22. Finally, the Symposium wished to record its gratitude to the Convenor of the Symposium, Professor T. Backiel, for his considerable energy and efforts in organizing and chairing the meeting.
23. Subsequent to the Symposium a restricted group of interested participants convened to consider further the action that should be recommended with regard to the code of practice. While supporting the principle of the need for such a code, this group felt that it was premature to adopt the code without further study. Further consideration was needed before an appropriate document could be submitted to EIFAC for adoption. It was therefore recommended that the existing ICES (International Council for the Exploration of the Sea) code submitted as document EIFAC/XII/82/171, together with supplementary information material, be referred back to the countries through the national correspondents for comments. These comments should be transmitted to the Working Party recommended above and to the Sub-Commissions in order to prepare a definitive proposal on this topic for the thirteenth session of EIFAC.
1 Documents presented to the session are listed in Appendix C
