Whereas specific conclusions relative to the various methods discussed are included in the individual panel reports, a general appraisal of the results and conclusions of the Symposium may be made by referring to the original objectives (see Section 1.2).
(a) to Review the present methods used in sampling the fish populations of lakes and large rivers. Over seventy contributions, and reviews for Panels 2 to 7 dealt with individual methods for surveying, monitoring or appraising fish populations. Particular attention was paid to:
the design and construction of gear;
its mode of action;
the conditions in which gear can be used;
the fish species, or groups of them, which can be sampled;
selection characteristics of the gear;
advantages and disadvantages in its use.
It was considered that the scope and detail of the information received was on a sufficiently large scale to form the basis for a manual on sampling methodology for fresh waters, although the importance of presentation of selected edited papers was also stressed.
(b) to Define the terms relative to methodology for the survey, monitoring and appraisal of fishery resources.
A possible approach to the definition of the terms was presented in the background document (EIFAC/SC-I-Symp.53) and the subject was discussed in Panel 1. It was, however, decided that this matter was too complicated to be considered fully by the Symposium. Therefore, although attention was drawn to the need for some common definition of terms it was not considered useful to deal with the problem in detail at this meeting.
(c) to Discuss the analysis of catches for the assessment of the properties of gear in sampling, and the interpretation of sampling data to establish characteristics of, and changes in, fish populations.
Questions of analysis of catches were considered in detail by the relevant panels. It was, however, clear that much remains to be done at the conceptual level. There is particularly a need to broaden the list of attributes of fish populations, which can serve to indicate deterioration of their environment or of their productive capacities, as those used often lack adequate sensitivity for many purposes.
(d) to Propose new or improved methods to be used for such sampling.
This objective was attained through discussion in Panel 8 (see Panel Review Section 5.8).
(e) to Formulate a long-term programme of research on such problems for the Member Nations of EIFAC as well as other countries concerned.
Possible programmes for research were discussed both during the Symposium (Panel 8) and during the follow-up to the Symposium and during the Eighth Session of EIFAC. These resulted in Recommendation 74/5 (see Section 4).
It was also proposed that at some future date a lake, either of known fish population, or which can be completely poisoned, be selected in one of the Member Nations. A workshop could then be convened at which specialists in various methods could obtain estimates of the population. A comparison between methods could thus be made.
With regard to the questions posed by Sub-Commission III (Recommendation 70/20) (see Section 1), it may be concluded from the discussions of the Symposium that quantitative estimates of the abundance of fish populations, and many others of their attributes, can be obtained for most lacustrine populations and in certain populations of large rivers. However, for most populations of the larger rivers, it was emphasized that both quantitative estimates of population characteristics and, more important, an understanding of the ecology of such waters have not yet been adequately elaborated. It was further noted that sampling of shallow habitats in lakes is poorly developed in relation to the importance of these habitats to the total fish production of such water bodies.
