A. INTRODUCTION

There has been a long-standing concern with the effects of introduction of non-indigenous species into European rivers and lakes. Furthermore, whilst stocking with indigenous or introduced species is also a common management practice, there is little evidence for or against its general biological or economic effectiveness. The International Consultation on Fishery Resources Allocation (Vichy, France, 1980) and the Eleventh Session of the European Inland Fisheries Advisory Commission (EIFAC) (Stavanger, Norway, May 1980) both recommended that the current situation for managing stocks of fish in European Inland waters be reviewed. A Symposium on Stock Enhancement in the Management of Freshwater Fisheries was held in conjunction with the Twelfth Session of EIFAC (Budapest, Hungary, 1982) in response to these recommendations. The Symposium and the Session itself felt that a further examination of important questions was necessary and established the Working Party on Stock Enhancement with the following terms of reference:

1. 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

2. to review the present status of stocking and to elaborate guidelines for stocking with various species groups forming part of established fishery management practices.

In addition to EIFAC, the Exotic Fish Section of the American Fisheries Society (AFS) and the International Council for the Exploration of the Sea (ICES) have both been addressing this problem. The ICES initiative, which is by far the most advanced, has centred around its Working Group on Introductions and Transfer of Marine Organisms. The Council adopted a first draft of the Code of Practice in 1973 and after six sessions the Working Group has now accrued considerable experience and is in an advanced stage of preparation of protocols for submission to its Council. The Exotic Fish Section of the AFS has been working principally to elaborate protocols for evaluating proposed fish introductions.

A meeting of the Working Party was held in Hamburg, 16–19 May 1983, under the chairmanship of Prof. K. Tiews with membership as listed in Appendix I, to discharge the terms of reference recommended by EIFAC, and to suggest means for cooperation among the three interested bodies to harmonize their approaches to the topic.

B. INTRODUCTIONS AND TRANSFERS

1. REVIEW OF CURRENT INITIATIVES

ICES: At its Statutory Meeting in 1973, ICES adopted a Code of Practice to Reduce the Risks of Adverse Effects Arising from Introduction of Non-indigenous Marine Species. At its Statutory Meeting in 1979 the Council adopted a revised Code. Interpretations of the Code, as well as pertinent definitions, are elaborated in the report.

The Council's Working Group relating to this matter met the week prior to the EIFAC Working Party Meeting on Stock Enhancement. At this meeting several new initiatives were brought forth to refine the machinery to implement the Code. The Working Group categorized introductions under three headings: (i) new species for commercial purposes; (ii) new species for scientific purposes, and (iii) species of common commercial practice.

Five specific protocols have been elaborated for the inspection of: (i) molluscs; (ii) crustaceans; (iii) marine fish; (iv) salmonid fish, and (v) molluscan hatcheries. These protocols have been practically-oriented, and are primarily directed at pathological considerations. The ICES Working Group recognized obvious gaps in this approach and have commenced development of additional protocols, including one on quarantine procedures, to cover other risk factors, as well as guidelines for the implementation of the protocols. Generally, the protocols are meant to be perceived as checklists of procedures to be followed when making introductions. In some cases, the protocols represent the “ideal” rather than the practical approach. The ICES Working Group intends to incorporate aspects of the Review and Decision Model developed under the auspices of the Exotic Fish Section of the American Fisheries Society. The model will be used as a vehicle for conducting feasibility and evaluation analyses.

AFS: The Exotic Fish Section of the American Fisheries Society was formed at its Annual Meeting in 1980. As one of its first initiatives, a Protocol Committee was established. A Suggested Protocol for Evaluating Proposed Exotic (= Introduced) Fish Introductions in the United States was developed and presented at the Section's symposium held at the Annual Meeting of AFS in Albuquerque, New Mexico, in 1981. This protocol was revised (Appendix 2) and presented at the EIFAC Symposium on Stock Enhancement held in Budapest, Hungary, in 1982. The protocol was suggested for implementation on both sides of the Atlantic. The protocol is primarily an evaluation tool and is presented as a flow chart in the form of a decision tree. The protocol is proposed as an effective mechanism for considering progressively more complex and uncertain information to arrive at decisions to approve or reject proposals for exotic fish introductions. As with the ICES's initiative, the protocol is considered as a reasoned approach to reduce the risk from introductions of exotics, and is not being proposed as an obligatory policy.

2. ITEMS ARISING IN DISCUSSION

This EIFAC Working Party discussed and reviewed the documentation submitted for its consideration (see Appendix B.I) and reached the following conclusions and recommendations:

1. Because EIFAC, ICES and the Exotic Fish Section of the AFS have similar interests in the application of a Code of Practice and accompanying protocols, it was recommended that the three Organizations harmonize their Codes and Protocols so that they are essentially similar. To this end, it was further recommended that the EIFAC Working Group on Introductions and the ICES Introductions Working Group should maintain close communication with each other, through exchange of working documents, correspondence between Chairmen and periodic joint meetings as feasible. Additionally, liaison with the Exotic Fish Section of the American Fisheries Society should be maintained by both Working Groups. Furthermore, in view of the worldwide interest in the potential dangers and advantages of Introductions and Transfers, as expressed in sessions of the Comision de Pesca Continental para America Latina (COPESCAL), Committee for Inland Fisheries of Africa (CIFA) and Indo-Pacific Fisheries Council (IPFC), the Working Party recommended that the Code of Practice and the Protocols it develops should have global application and should be made available to other interested national and regional groups.

2. That once a species has crossed a national border, it must be regarded as effectively introduced into the receiving country regardless of the precautions which are taken to keep it isolated from the natural environment.

3. That two levels of documentation are necessary for the complete implementation of an international policy for the reduction of risks of adverse effects arising from introductions.

   1. A Code of Practice: a general guideline and statement of policy which can supplement local legislation, and which is supported by

   2. Protocols: practically-oriented checklists for implementation of the Code of Practice. These need to be elaborated and kept under review to reflect changing needs of the fisheries and to benefit from experience gained during their implementation.

   It was recognized that while neither the Code of Practice nor the Protocols have the status of law, they do imply a strong moral obligation. They, therefore, serve principally as guidelines, although, once accepted in principle, certain provisions, for example a Protocol on Quarantine, are so basic that their rigid application becomes mandatory.

4. The Working Party recognized the many practical difficulties inherent in the implementation of a Code of Practice to regulate the introduction and transfer of fish species from one country to another. It also took into account the feelings of some countries that their internal legislations were sufficient for their own needs. Nevertheless it felt strongly that were the Commission not to attempt to establish a position on the issue by the publication and eventual implementation of such a Code and its accompanying protocols it would be failing in one aspect of its duties. It was therefore recommended that the Commission at its next session adopt the Code of Practice as presented herein.

   It further recommended that EIFAC appoints a standing Working Group of national representatives to implement the Code according to the procedures laid out below and elaborate such protocols as are deemed necessary for its implementation. The Working Group should work primarily by correspondence and meet during the sessions of EIFAC and at such other times as may be necessary. It should itself be free to form ad hoc task forces for the detailed consideration of specific organisms.

   At a first task the Working Group should establish appropriate protocols for realizing introductions taking into consideration the procedures already elaborated by ICES.

5. The suggested procedure for considering requests should be:

   1. A documented proposal for introduction or transfer of a new species of fish either from a country outside Europe into Europe, or between European countries, should be transmitted via the appropriate Government authority to the National EIFAC correspondent. This assumes that such an introduction would not contravene national laws and that the earlier steps of the Protocol for evaluating introductions would already have been completed by the proposer.

   2. The National Correspondent would forward the request to the Secretariat of EIFAC, accompanied by documentation on the scope and purpose of the introduction, the source of the stocking material, the locality into which it is to be stocked and as much detail on the biology and ecology of the species as is available.

   3. The Secretariat would transmit this to the Chairman of the Working Group.

   4. The Working Group would then consider each request, passing it to a task force if necessary, and would recommend the rejection or acceptance of the proposal or request further information according to the Protocols laid down for evaluating proposed introduction.

   5. The advice of the Working Group should be transmitted through the appropriate Sub-Commission to the plenary session of EIFAC for endorsement.

   6. This decision would then be transmitted by the Secretariat to the National Correspondent who would inform the original proposer.

   7. The Commission may consider giving a mandate to the Chairman of the Working Group to directly communicate advice to the proposer via the National Correspondent in exceptional circumstances.

Flow chart for considering requests

3. THE PROPOSED CODE OF PRACTICE

Proposed Code of Practice to reduce the risk of adverse effects arising from the introduction or transfer of inland aquatic organisms.

(a) Recommended procedure prior to reaching a decision regarding proposed introductions

(This procedure does not apply to introductions or transfers which are part of current commercial practice).

1. Member countries contemplating any introduction should be requested to present to EIFAC at an early stage information on the species, area of origin, proposed place of introduction and objectives, with such information on its habitat, associated organisms, etc., as is available. EIFAC should then consider the possible outcome of the introduction and offer advice whether to proceed with further evaluation.

2. Appropriate authorities of the importing country should examine each “candidate for admission” to assess the justification for the introduction, its relationship with other members of the ecosystem, details of its biology and ecology and the possibility of introducing associated pathogenic organisms and parasites.

3. The probable effects of introduction into the new area should be assessed carefully, including an examination of the effects of any previous introductions of this or similar species in other areas, and a prediction of the final range of the species assuming it could form breeding populations in natural waters.

4. The above procedures (i, ii, iii) should be carried out by following the Review and Decision Model as set out in the subsequent section.

(b) Recommended action

If the decision is taken to proceed with the introduction, the following action is recommended:

1. A brood stock should be established in an approved quarantine situation. Brood stocks should be developed from stocks imported as eggs, in order to minimize the possibility of contamination by pathogenic organisms, parasites or by other species of fish. Should this not prove possible, every effort should be made to obtain stocks certified free of specified pathogens or at least to arrange for prophylactic treatment in the country of import on arrival. All effluents from establishments used for guarantine purposes should be sterilized in an approved manner.

2. If no communicable pathogenic organisms including parasites become evident, the first generation progeny, but not the original import, of the introduced species can be transplanted to culture sites, or to the natural environment, preferably to small, isolated and restricted river basins or lakes.

(c) Recommended actions after introduction:

1. A continuing study should be made of the introduced species in its new environment and progress reports submitted to EIFAC.

2. Every effort should be made to contain the species within the water bodies or water courses into which introduction was intended.

(d) Regulatory agencies of all member countries are encouraged to use the strongest possible measures to prevent unauthorized or unapproved introductions and transfers

(e) Recommended procedure for introductions or transfers which are part of current commercial practice

The procedures laid down by the “Draft Convention to prevent the spread of major communicable fish diseases” should be adhered to, especially:

1. Periodic inspection (including adequate microscopic and microbiological examinations) by the receiving country of material for prior mass transplantation to confirm freedom from introducable communicable pathogenic organisms and parasites. If inspection reveals any undesirable development, importation must be immediately discontinued. Findings and remedial actions should be reported to EIFAC.

2. Inspection and control of each consignment on arrival.

3. Quarantining or disinfection where appropriate.

4. Establishment of brood stocks certified free of specified pathogens.

(f) Definitions pertaining to the Proposed Code of Practice

For the application of this Code, the following definitions should be used:

1. Introduced species (= non-indigenous species; includes both non-indigenous and exotic species): Any species intentionally or accidentally transported and released by man into an environment outside its present range.

2. Transferred species (= transplanted species): Any species intentionally or accidentally transported and released within its present range.

3. Quarantined species: Any species held in a confined or enclosed system that is designed to prevent any possibility of the release of the species or any of its diseases or any other associated organism into the environment.

4. Exporting country: The country from which a specific consignment of a species (regardless of its native region) is received.

5. Country of origin: The country where the species is native.

6. Country of receipt (= importing country): The country to which a specific consignment of a species is sent for introduction, transfer (in the sense of (ii)) or quarantine.

7. Brood stock: Specimens of a species, either as eggs, juveniles or adults, from which a first or subsequent generation may be produced for possible introduction or transfer.

8. Current commercial practice: Established and ongoing cultivation, rearing or placement of an introduced or transferred species in the environment for economic or recreational purposes.

4. REVIEW AND DECISION MODEL FOR EVALUATING PROPOSED INTRODUCTIONS OF AQUATIC ORGANISMS INTO AND WITHIN EUROPE

The model (Fig. 1) is composed of five levels of review and five corresponding “Decision Boxes”. Components of the model are described below, with decisions being based on scale values obtained from an “opinionnaire” (Table 1).

(a) Proposal for introduction of aquatic organisms

An entity desiring to realize an introduction would prepare a proposal that includes the answers to the following questions:

1. What organism do you propose to introduce (common and scientific name)?

2. What is its native range? What is the present range?

3. What is the purpose of the introduction?

4. Where and into what type of system would this organism be introduced and how many would be introduced?

5. What precautions have been or will be taken to ensure that the organisms are not harbouring communicable pathogenic organisms and parasites?

6. If the organisms are to be maintained in a closed system, what measures would be taken to guard against accidental escape to open waters?

7. What is the current state of knowledge concerning the acclimatization potential of the organism?
   e.g., (a) Thermal requirements: tropical, temperate, Arctic; (b) Habitat requirements: stream, river, lake, pond, etc., (c) Reproduction: describe the spawning habitat and reproductive strategy of the organisms.

A bibliography of pertinent literature should be appended to the proposal.

(b) Level of Review I

1. Purpose of introduction
   Does the proposing entity have valid reasons for introducing the aquatic organism? Could no native species serve the same function?

2. Abundance in native range
   Knowledge of the population abundance of the organism in its native range is an important aspect of the evaluation. Is it endangered, threatened or rare? Is it exploited from the wild or under culture?

3. Communicable pathogenic organisms and parasites
   The evaluation would include assessing the safeguards for avoiding transmission of communicable pathogenic organisms or parasites to the proposed receiving system(s).

4. Site of introduction
   It is important to discern from the outset whether the organism would be stocked in an open or closed system. Would it be stocked in or have potential access to a major drainage? If it is to be maintained in a closed system, the proposing entity must identify steps it would take to guard against accidental escape.

(c) Decision Box I

A proposal for an introduction would be rejected if:

1. reasons for introduction were not deemed valid;

2. the introduction is for reasons other than conservation where the organism is endangered, threatened, or rare in its native range; or

3. the proposing entity has not established that adequate safeguards would be taken to avoid introduction of communicable pathogenic organisms and parasites. The proposal would be approved at this stage when the above criteria are met and provided that the introduction is perceived as being limited to a closed system. When this last condition is not fully met, the evaluation process would proceed to the next level of review.

(d) Level of Review II

This and subsequent levels of review are directed to experts selected by the Working Group. In Level II, the acclimation potential is assessed (question 5 of the “opinionnaire”, Table 1). Should pertinent information be insufficient, as evidenced by more than 50 percent of the experts marking “don't know” on the “opinionnaire”, the Working Group might suggest that the proposing entity conduct research with a limited number of specimens under confined conditions for the purpose of obtaining the required data. The Working Group may suggest that all research be conducted within the organisms' native range.

(e) Decision Box II

The proposal for the introduction would be approved when there is a strong chance that the organism would not establish a self-sustaining population (average value≥ 3 for question 5 in Table 1). Alternatively, further evaluation would be mandated for those organisms that would likely produce self-sustaining populations, or when evidence is insufficient for making a seasonable prediction.

(f) Level of Review III

This level of review is based on predicting the potential impact of the organism on the ecological integrity of the system(s) where it is proposed for introduction. In addition, the analysis of benefit and risk would include assessing the array of potential impacts on man. Review at this level requires detailed knowledge on the ecological relations of the organism in its native habitat, as well as considerable information on the community structure of the proposed receiving system(s).

(g) Decision Box III

The introduction would be rejected if the available information suggests (average “opinionnaire” values≤ 2) that the organism would exert a major adverse impact on the receiving system(s) or on man. The proposal would be approved when indications are for the opposite outcomes. If the available information is not considered conclusive, the evaluation should proceed to level at Review IV.

(h) Level of Review IV

Level of Review IV requires development of a detailed literature review based on the format for a Food and Agriculture Organization (United Nations) Species Synopsis. However, additional sections concerning impacts of introduction (documented or potential) would also be required. Once the synopsis is prepared, this information will be sent again to the experts so they can attempt to arrive at a recommendation.

(i) Decision Box IV

On the basis of an analysis of the second round of “opinionnaire” data, the Working Group would either approve or reject the proposed introduction. Additional review (Level V) would be necessary whenever the current data base is not considered sufficient, or if it is unclear whether the introduction is desirable.

(j) Level of Review V

This level of review requires that research be conducted to complete the species synopsis or to assess the potential impact of the introduction on the indigenous flora and fauna and habitats. It might be suggested that research be conducted under controlled conditions near the site where the introduction is contemplated or the Working Group may suggest that all studies be carried out within the organisms' native range.

(k) Decision Box V

Using all information collected at this stage, the Working Group should be able to make an informed recommendation regarding the proposed introduction. However, the Working Group may find it necessary to suggest additional research if important questions remain to be resolved. In such a situation, the fifth and final evaluation stage would become a loop of the “Review” and “Decision” models until a recommendation could be made.

Table 1 Opinionnaire for appraisal of introductions of aquatic organisms. Each member of an evaluation board or panel of experts circles the number most nearly matching his/her opinion about the probability for the occurrence of the event. If information is unavailable or too uncertain: “don't know” is marked
(Kohler and Stanley, in press)

Table 2 Review and Decision Model for evaluating proposed introductions of aquatic organisms. Mean “opinionnaire” values (see Table 1) are used at decisionmaking points (Kohler and Stanley, in press)

5. OTHER CONCLUSIONS AND RECOMMENDATIONS

1. Because the administration of the Code of Practice and its associated Protocols rests entirely on voluntary adherence to guidelines and because many user groups have attitudes to introductions that are contrary to those of the Commission, education of the user groups is essential for the voluntary application of the Code. To assist in this it was recommended that wider publicity be given to the potential dangers of uncontrolled introductions. One method would be the compilation of simple case histories of introduction which have had bad effects, which could be published in the angling press. The Code of Practice itself could eventually be disseminated in a similar manner.

   It was further recommended that the report of this Working Party be transmitted to IUCN and the World Wildlife Fund for information.

2. Specimens representative of the introduced species should be deposited at the time of introduction in a recognized scientific institution. Such specimens should be derived from the actual population introduced at the time of introduction or release and should be prepared and preserved (fixed) following standard methods, including those methods (such as embedding) that would permit histological studies in the future.

3. To increase understanding of the legislations governing introduction of aquatic organisms into the inland waters of member countries of EIFAC it was recommended that the Working Party compile the relevant national laws for publication as a technical paper of EIFAC.

APPENDIX B.I

List of documentation considered by the Working Party

1. Report of the Working Group on Introduction and Transfers of Marine Organisms, ICES, C.M. 1982/F:37

2. Letters from Backiel (Poland), Henri (U.K.), Timmermans (Belgium), Dahl (Denmark), Stephanou (Cyprus) and Thuransky (Hungary) commenting on the Code of Practice as presented in EIFAC/XII/82/17

3. Proposed ICES Guidelines for Implementing of Code of Practice (ICES, C.M. 1982/F:33)

4. The ICES Working Group's document on protocols for inspection of marine organisms prior to importation

5. Kohler's paper on Implementation of a Review and Decision Model for Evaluating Introductions in Europe and North America

6. Report of the Symposium on Stock Enhancement in the Management of Freshwater Fisheries, EIFAC/T.42

7. Conservation of the Genetic Resources of Fish: Problems and Recommendations, FIRI/T.217

8. Register of International Transfers of Inland Fish Species. FIRI/T.213

9. A Suggested Protocol for Evaluating Proposed Exotic Fish Introductions in the U.S.A. by Kohler and Stanley

10. Introduced Fish Terminology by Shafland and Lewis

11. Further comments on Code of Practice by EIFAC correspondents

C. STOCKING

1. BACKGROUND

It was concluded at the Symposium on Stock Enhancement in the Management of Freshwater Fisheries (Budapest, 31 May–2 June 1982) that, despite a long history of stocking with many species in the inland waters of Europe, little knowledge of the ecological and economic implications of these activities exists. It is, however, apparent that despite some successes much of current stocking practice is misdirected and ecologically and economically unproductive.

2. RESULTS OF DISCUSSIONS

The appended papers by Backiel (Appendix C.1) and Grimm (Appendix C.II) were presented and discussed. The Working Party felt that it had little to add to their conclusions and those of the Symposium at this time. However, the following items were identified as of particular significance.

1. Definition: The intentional release of aquatic organisms with the aim of utilizing the natural biological productivity of natural or artificial waters such as reservoirs other than fishfarm ponds or other intensive units.

2. The purpose for stocking may condition the procedures and policies whereby it is carried out and thus also influence the guidelines needed. The following purposes for stocking were identified although items would need further elaboration and refinement.

   1. Compensation: To provide for a phase in the life cycle suppressed by human intervention (the stock would disappear without stocking)

   2. Maintenance: To sustain stocks in face of environmental or fishing pressures which prevent their reaching natural carrying capacity.

   3. Enhancement: To keep the production of stocks above the level that would be naturally sustained in the presence of heavy exploitation.

   4. Put-and-take: To provide catchable-sized fish for rapid exploitation by anglers (minimal environmental input)

   5. Put-grow-and-take: To provide fish that must grow to a catchable size before exploited by anglers (some environmental input)

   6. Re-population: Establishment of a unit stock of community in waters from which it has previously been eliminated.

   7. Increase diversity: To augment the range of species available to a fishery

   8. Niche filling: To provide stocks to utilize a trophic or spatial resource which is perceived as unexploited.

   9. Forage: To provide a prey species to enhance the production of angling or commercially exploited species

   10. Pest control: To provide organisms to control flora or fauna perceived as unfavourable to man

   11. Environmental improvement: To provide organisms expected to favourably modify the system.

   12. Conservation: To maintain genetic diversity (as to convserve endangered species or stocks)

3. Because of the general lack of information on stocking in Europe it is recommended that a Working Party on Stocking be established to:

   1. review European policies and practices for stocking inland waters;

   2. encourage cooperation in the research and monitoring of stocking practice;

   3. establish guidelines for stocking of selected fish species.

4. The membership of the proposed Working Party should include a selection of experts in various aspects of stocking and it was suggested that the following be approached to form a core group:

   M. Grimm (Netherlands)
   A. Lelek (Federal Republic of Germany)
   J.C. Phillipart (Belgium)
   F. Kennedy (Northern Ireland)
   K. Mann (United Kingdom)
   K. Salojarvi (Finland)
   M. Bninska (Poland)
   J. Holcik (Czechoslovakia)
   C. Moriarty (Ireland)
   A. Raat (Netherlands)
   B. Holmberg (Sweden)
   To be nominated (France)

   The core group should seek to involve other workers on stocking and it is also suggested that representatives from the U.S.A. and Canada be invited to participate.

APPENDIX C.I

Discussing guidelines for stocking

T. Backiel, Poland

1. WHAT IS STOCKING?

The “proposed guidelines for implementation of the ICES Code of Practice concerning introductions and transfers of marine species” (ICES, CM^1982/F:33 Mariculture Committee) contain several definitions relevant to the contemplated guidelines for stocking. Here “transferred species” (= transplanted species) are defined as any species intentionally or accidentally transported and released within its present range. This definition includes the intentional release of any established species into waters within its present range, which should be separately defined as “stocking”.

The purpose of stocking, in the sense considered here is to utilize the natural biological productivity of natural or artificial waters such as reservoirs but excluding fishfarm ponds or other intensive rearing units.

2. STOCK CONCEPT

Stocking any lake with fish species derived from another lake may have implications and consequences which differ from those resulting from stocking the same lake with fish originating from its own waters. It is important to keep in mind intraspecific diversity of species and the Stock Concept Symposium, 1981 (Can.J.Fish.Aquat.Sci., 38, No. 12) particularly emphasized the importance of genetic variability at that level.

3. BROAD CONSIDERATIONS OR PRECISION

There is a well known conflict between simplicity and precision in the statistical treatment of data. A similar conflict is often observed in applied sciences, where practitioners would like qualitatively and quantitatively precise recommendations on what to do and on the results of their doing it. This is seldom possible and in the case of stocking one can even quote quite old proposals, for example, Leger (1910) “Principes de la methode rationelle du peuplement des cours d'eau a salmonide”, Trav.Lab.Pisciclt.Univ.de Grenoble, or G.C. Embody (1928) “Stocking policy for streams, smaller lakes and ponds of Oswego watershed”, N.Y.Cons.Dept.Supp.to 17th Ann.Rept., where the authors gave quite precise recommendations on where and what and how many fish should be stocked.

Managers nowadays seem to be dissatisfied with such “precise” methods and more generalized models are being sought, which give quicker and cheaper answers. A compromise should be sought between broadness and precision.

4. SOME OTHER RELEVANT CONCEPTS AND IDEAS

Whatever the motive for stocking, it may be expected that at least some of the fish stocked will survive and grow to a catchable size. Survival and growth are basic components of population dynamics and it seems useful to take it into consideration here. A time-space trajectory of a cohort of stocked fish can be visualized as follows:

Besides survival and growth, quantitative aspects of a trajectory consist of fecundity, developmental periods (e.g., larval period, age at maturity), movements, space inhabited, density. There are obvious difficulties in estimating and in predicting all of these parameters in the case of a stocked cohort, but some of them could be found for the species of fairly well known life histories. They are useful in contemplating stocking.

With multi-species fish stocks the difficulties of applying the classical population dynamics concept on models are so great that one has to look for some other basis for management. This is also true where there are many small stocks of a species, for example, brown trout in many streams, The idea of some form of fish community succession as a response to natural or induced changes of the environment has been “re-discovered” and considered useful in management. (I consider this a rediscovery of old fishery typology of lakes well known in Central Europe and in the U.S.S.R., e.g., a series of whitefish, bream, pike and tench, and zander lakes (Barthelmes, 1981, Hydrobiologische grundlagen der Binnenfischerei, Jena) or a more complicated Soviet or Polish series of whitefish, bream, bream and smelt, bream and bleak, zander, perch and roach, crucian carp lakes.

At the last EIFAC Symposium on Stock Enhancement in the Management of Freshwater Fisheries, several other concepts were presented which deserve attention while discussing guidelines for stocking. The niche concept with its derivatives - niche overlap, realized niche, niche shift, etc.-dominance, subordinance in fish communities (see Svardson, 1976, Rep.Inst.Freshwat.Res., Drottningholm 55: 144–71) are examples of this kind of idea devised, inter alia, to explain facts or artefacts a posteriori.

5. HOW TO ASSESS APPROPRIATENESS FOR STOCKING

There are two main questions to be answered: can stocking with species × improve the fishery in water W? and, what effect on other fish or the environment can be expected? The first is of a qualitative nature and in trivial situations can easily be answered.

Consider a desired species of well known life history and ecological requirements, then two extremes can be envisioned:

1. The environment in question is obviously suitable and fishing is intensive, then stocking for put-and-take fisheries could be justified.

2. Environment is obviously unsuitable (e.g., for brown trout alvins, a warm eutrophicated lake), then stocking would be a waste of time.

The scope for survival of reasonably stocked fish is almost 100 percent in the first case and it is nil in the second case. There is probably an infinite variety of intermediate situations between these two extremes but, perhaps, we could reduce this variety by considering:

An obvious situation would be the destruction of or inaccessibility of spawning grounds - as in Baltic salmon - which, taking into account the economic aspect, justifies releasing hatchery-reared fish.

When speaking of scope for survival, it should be assumed that the stocked fish are subject to the same processes of mortality as natural populations of the same size. Obviously, where density-dependent factors influence mortality the pre-existing density of the species to be stocked must also be taken into account.

6. HOW TO ASSESS NUMBERS FOR STOCKING

One approach to the assessment of quantitative stocking is by means of the following “rule of thumb”: a rough estimate of annual catch by weight, divided by the annual rate of exploitation gives an estimate of the mean biomass of catchable stock; the biomass annually recruited to this stock can be roughly estimated from literature on most common species - as a percentage of the catchable stock, then the contemplated or ongoing stocking is compared with the recruited biomass.

For example, let U-rate of fishing be 0.3, and annual recruitment be 0.08 of catchable stock (figures from Backiel, 1971, in J.Fish Biol., 3:369–405, on piscivorous fish in the Vistula River), then recruitment is 27 percent of catch by weight. Any stocking programme of, say, 2–5 percent of catch would be at least difficult to assess as its effects, as natural fluctuations will dampen effects of stocking. There seem to be some data available in literature from which a range of the two parameters can possibly be extracted.

A second approach suggested by Welcomme (1976) Involves the estimation of potential yield from a water body using the Morpho-Edaphic Index. The number of fish to be stocked can then be estimated from:

7. ESTIMATION OF THE EFFECTS OF STOCKING

Several groups of methods basic to the success or failure of stocking come to mind:

-   stocking rate versus catch with due consideration of time lag, as exemplified at the EIFAC Symposium in Budapest with regard to eel;

-   marking and tagging (many studies have been carried out);

-   stock identification as that utilized in genetical research (protein electrophoretic analysis revealed effects of stocking - see Altukhov, 1981, and Ryman and Stahl, 1981, in the volume of Stock Concept Symposium, quoted above);

-   analysis of opinions of, say, sport fishermen.

Technical problems on the interface between aquacultureal techniques and procedures of stocking have been considered in the past and at the EIFAC Symposium in Budapest. To what extent should these be discussed by the Working Party? This may include handling fish as well as problems of fish diseases.

APPENDIX C.II

Towards the formulation of guidelines for stocking of fish

M. Grimm, The Netherlands

1. INTRODUCTION

Stocking of fish (= to supply waterbodies within the geographical distribution range of a species, with individuals of that species, within a certain life-stage) is a widespread practice. The results of stocking, however, appear to vary with species, life stages and with locations and management goals.

The introduction of eel and elvers, the stocking of salmon smolts and the release of trout fingerlings (all stockings executed in response to the blocking of migration pathways (to the “grow-up” or spawning habitat) and/or in response to deterioration of spawning substrate) are reputedly successful.

The stocking of fingerlings of predator species (northern pike, pike-perch, trout) to increase population densities appears to be either totally unsuccessful (as in the case of northern pike), or serious doubt about the good results reported seems to be justified. Often the methods used to quantify the effects of stocking are focused exclusively on the individuals stocked. Marked fishes are stocked and the frequency of occurrence of these individuals in the catch realized is labelled as a contribution to the population. The alternative possibility, that naturally recruited individuals are replaced by the ones stocked, is mostly not considered. This reflects either the faith of fishery managers and scientists that, to a greater or lesser degree, a given input has to lead to a desired output, or it reflects the limited possibilities of managers and scientists to monitor the stocking effects on a more fundamental basis.

The faith or trust in the beneficial results of stocking might be responsible for the lack of basic evaluation studies on the introductions of many species. For example, the results of transfers and planting of roach, bream, adult northern pike and pike-perch in the Netherlands and Belgium appear to have been reported and/or evaluated only incidentally. The papers submitted to the EIFAC Symposium on Stock Enhancement deal primarily with the greater or lesser successes in stocking obtained, and/or with case studies in which effects observed could, in the author's opinion, be attributed predominantly to the stocking of a species. Hardly any successful stockings are reported. It should be stressed that cases of successful stock enhancement by means of stocking are quite rare. The reason appears to be that, despite the fact that quite extensive data are available on, for example, habitat preference, distributions in time and space, food preferences and predators, knowledge of the factors that determine the recruitment of individuals to the adult stage and/or catchable size is lacking.

Therefore the amplitude of the “natural” fluctuations in the abundance of most species is unknown and hence effects of stocking (especially of the younger life stages) cannot be measured.

Guidelines for stocking deal with (i) the short and/or long-term effects to be anticipated of the stocking of a given number within a given life stage or length range, (ii) the population density of the species stocked and (iii) the abundance and population structure of other species. In view of the methods of stock assessment mostly used it will be difficult to anticipate these effects by reviewing the available literature. Therefore, it is feared that at this moment guidelines for stocking can only be dealt with in very global terms. Successes in the stocking (of life stages) of some species might be underlined, the scepticism about the use of stocking of others might be stressed, while some species will get the benefit of the doubt as far as beneficial effects on the population density of the species are concerned. Information as to what extent other species are affected, seems to be hardly available and of a speculative character. In view of this it seems appropriate to consider the setting up of these guidelines as a long-term and iterative process.

A possible pathway to follow could be:

1. Inventory of: (a) the species stocked/transferred within member countries; (b) numbers stocked yearly in the last ten years; (c) stocking guidelines (number and weight/ha); (d) reported results;

2. Review of the data available in literature;

3. Formulation of provisional guidelines, recognition of information gaps, formulation of recommendations for stock assessment methods;

4. Continuously updating of guidelines.

An inventory as meant in (i) above will give an insight in several aspects of the stocking practice:

-   the economically most important species;

-   guidelines about the numbers stocked;

-   decreases or increases in numbers stocked, which could reflect the reported trust or scepticism fishery managers have in the product.

A review of the literature on stocking, as in (ii) above, which can lean heavily on the Budapest Symposium papers, can reveal the irrelevance of developing guidelines for a number of species or life stages. For example, a preliminary review on pike-perch fingerling stockings in autumn, suggests that this product will only be useful in introducing the species in a water body and not for stock enhancement purposes. Also, the stocking of trout fingerlings may be doubted in some cases, if only by their territorial behaviour.

Besides this, a literature review presents additional information on the stocking practice, while background information is furnished on the motives and philosophy of the stocking practice.

With regard to the formulation of provisional guidelines (step 3) it seems useful to formulate global directives based on expert experience, literature surveys and inventories of stocking practice within a period of 2–3 years. It is worthwhile encouraging member countries to assess stockings in future over long periods of time, by monitoring both catches as well as fish population dynamics. Population estimates, either by analysis of catch statistics or by mark-recapture methods over, say, five-year periods prior to and after stocking, are desirable. Programmes and facilities to furnish these data as a common practice should be stimulated. Data thus gathered are useful for refining and updating the provisional guidelines for stocking (step 4).

2. CLASSIFICATION OF STOCKING

It might prove useful as will be elaborated to some extent later, if stockings are classified according to the effects they have on the fish community and on the abundance of the species stocked. An alternative classification can be based on the management goal. In this paper, however, we consider the fish population as the natural basis of classification. Two main types of stocking can be discriminated:

1. To establish a species, whether or not by continuous stocking, within a water body situated within the geographic distribution range of the species, where it did not occur till then. For example, pike-perch in the Netherlands might be considered an autochthonous species by now, however there are quite a number of waters where the species does not occur and where it could be introduced. Also the stocking of carp might be considered in a number of waters as an introduction. Within this group both long-term (one year and over) as well as short-term management goals can be distinguished. Short-term management goals as, for instance, put-and-take trout fisheries, could even be met by introducing fish in water bodies where their habitat requirements are not met.

2. To support or enhance a naturally sustaining species present in a water body for ten years and over:

   1. to counteract a decrease in numbers (e.g., to preserve a species);

   2. to maintain a maximum number;

   3. to enhance the maximum number.

   The majority of type (ii) (a) and (b) management goals that are directed on long-term effects are pursued by stocking early life stages. Type (ii) (c) often deals with the stocking and/or transfer of relatively large individuals. This method is concerned with short-term effects. It seems appropriate for our Working Party to disregard species conservation purposes because only exploitable stocks are of interest to fisheries.

3. FRAMEWORK FOR PROVISIONAL GUIDELINES

For the purpose of setting up provisional guidelines of stocking the two classes (i) and (ii) demand a different approach. In the case of class (i) guidelines for stocking should cover amongst other things:

-   habitat requirements;

-   possibilities of natural reproduction;

-   minimum abiotic conditions required to establish the species;

-   possible niche overlap with autochthonous species.

Due to our lack of knowledge of the factors regulating the abundance and population structure of the autochthonous species and of the species introduced, the consequences of the class (i) introductions are difficult to predict. The more or less conflicting evidence of the consequences of pike-perch introductions, as put forward at the Stock Enhancement Symposium, illustrates this.

Considering our present knowledge, the best way to deal with such stocking is in terms of the introduction of exotics. An appropriate approach in the setting up of guidelines is to follow the “Implementation and Decision Model” of Kohler and Stanley (Stock Enhancement Symposium). However, it seems highly preferable to proceed no further than to Decision Box II: no successful reproduction, either to abiotic or biotic factors or by the introduction of monosex of infertile individuals. In the case of class (ii) stockings, it is apparent that conditions for natural reproduction, habitat requirements, etc., are met, although possibly to a lesser degree due to manmade alternations. The consequences of restoring dwindling populations of a species on the fish community might in some cases be predictable by using catch statistics from the “good old years”.

Class (ii)(a) and (ii)(b) stocking guidelines will concentrate on the deteriorations of the environment especially spawning and “growing-up” habitats. It should be stipulated that stocking of early life stages are rational if:

1. the habitat requirement of the species from that stage on are met;

2. the conservation of the genetic variability of the stock is guaranteed (FAO Fish.Tech.Pap., 217);

3. the introduction of (hatchery-born) diseases is prevented;

4. the vulnerability of the stocked fish to predation is the same or lower compared to the native stock;

5. the mortality resulting from handling at stocking if negligible.

In the case where stocking guidelines are given for the purpose of preserving a species, attention could be paid to the effects of habitat-improvement (e.g., the enlargement of sheltered places in brooks instead of stocking trout) and changes in the quality of the water.

4. PROPOSED PLAN OF ACTION

In the Introduction we distinguished between four groups of activities that are essential for the formulation of guidelines for stocking. With regard to these groups we propose to plan the following activities.

1. Make an inventory of stocking practice. An inventory of stocking practice can be made in 1983/84. Coordination by the EIFAC Secretariat or Working Party (questionnaires to EIFAC correspondents and/or persons/institutes)

2. Literature reviews of stocking practice and results and effects of stocking. It is suggested that EIFAC/FAO supplies relevant literature references by means of the ASFA and BIOSIS information systems. It seems advisable that some species literature from Eastern Europe is covered by authors from that region. Prof. Backiel can perhaps suggest authors (Dr. Berka?). Relevant literature information from Western Europe, Canada and North America can be covered by authors from that region, of course in close cooperation with the author(s) from Eastern Europe. The reviews should be completed within the period 1983–85. The editing of the manuscripts can be done by M.P. Grimm. The Organization for the Improvement of Inland Fisheries (the Netherlands) is prepared to undertake reviews on cyprinids, percids and esocids of the stagnant waters. Authors for cyprinids of running waters, salmonids and coregonids must be proposed and/or selected.

3. Formulation of provisional guidelines, information gaps, stock assessment methods. As a result of (i) and (ii) provisional guidelines can be formulated by the Working Party. The Working Party and EIFAC Secretariat can stimulate member countries to establish programmes and facilities for assessment of stocking results and effects.

4. Updating guidelines can be coordinated by the EIFAC Secretariat.

APPENDIX I

List of members and observers of EIFAC Working Party on Stock Enhancement

Hamburg, Federal Republic of Germany

16–19 May 1983