RESERVOIR STOCKING IN LATIN AMERICA, AN EVALUATION (Contd.)

6. CONCLUSIONS

The relationship between fish yield and stocking density is a good indicator of stocking success when maximising biomass is the management objective. As expected, for self-sustained fish populations, stocking is not a good management measure when insufficient recruitment to the fishable population has not been observed. Supplemental stocking programmes may be justified in some other cases (White et al., 1995), but generally are undesirable from an economic standpoint when managing for biomass is the main objective. Supplemental stocking is one step in the process of increasing yields from natural capture and recreational fisheries to intensive aquaculture (Welcomme, 1995a).

For introduced species that need the continuous addition of young fish to develop fishable stocks, stocking must be suited to the reservoir's natural carrying capacity (climate and morphoedaphic factors) (Mari and Quiros, 1986; Quiros, 1994; Fonteles-Filho and Alves, 1995), to diffuse external organic matter inputs, and to external inputs of fertilisers and food (Song, 1980; Lu, 1992; Quiros, 1994; among many others). Surface area had no effect on fish yields in tropical Latin American reservoirs, after stocking rate, mean fish weight at stocking, and intensification grade effects had been accounted for.

Based on this study, a general pattern for Latin American reservoirs was prepared (Box 1). It can be used as a tool for rationalising stocking, to assess stocking programmes, or to correct mismanagement and obtain successful outcomes.

7. RECOMMENDATIONS

Stocking is not a magic management measure for resolving almost any problem in freshwater fisheries. For the region as a whole, despite considerable differences, current stocking practices (Olmos et al., 1992; Fonticiella et al., 1995; Fonteles-Filho and Alves, 1995; among many others) have to change from random stocking to decisions based on the productive capacities of water bodies, sound fisheries enhancement measures, and fish community compatibility, rather than trying to exceed natural or actual capacity just with stocking. Random supplemental overstocking is not the best way to enhance freshwater fisheries. Stocking should be suited to the presence of self-sustained fish populations and should be assessed for each reservoir.

When the objective is to maximize the biomass, stocking should be matched with inputs of fertilisers and food, as exemplified by some Cuban semi-intensively managed small reservoirs, and ponds and very small reservoirs in northeastern Brazil. Supplemental stocking programs for self-sustained fish populations in Latin American reservoirs need to be studied and analysed on a case-by-case basis.

Latin America is a very heterogeneous socio-economic region. Fisheries governmental agencies as well as public and private fishery managers have to be aware of stocking limitations for enhancing fish production in freshwater fisheries. When economic analyses of stocking programmes are negative, considering social benefits may compensate for the losses, but environmental impairments may, in turn, cancel some of the social benefits. However, it is not advisable for most of the countries in Latin America to evaluate stocking programmes on economic basis alone.

Welcomme (1995) suggested stocking can be a highly cost-effective way to increase fish production. In some regions worldwide stocking is considered highly profitable. However, for Latin America as a whole, many stocking programmes have had dubious results. Motivation for such programmes has been very often based on public pressure or political constraints. Some technical mismanagement measures might be easily corrected. Where social and economic considerations are required, a preliminary programme assessment is highly appropriate.

Annex I. Data base for Latin America aquatic environments.

Country:
2) Cuba,
3) Mexico,
4) Brazil,
6) Peru,
7) Venezuela,
8) Costa Rica,
9) Other

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