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P.A. Siri and A.F. Born
FAO, Department of Fisheries, Rome, Italy


This consultation has reviewed a number of enhancement projects in widely differing biomes and cultures. It is difficult, perhaps impossible to establish a predictive model that would determine project success. However, some trends can be defined when projects are categorised according to technological, biological and socio-economic criteria. Technologically, stocking criteria for lakes and reservoirs and predictable yield and growth based on physical and limnological characteristics are becoming increasingly systematic. Similarly, advances in cage culture in a variety of habitat and countries are demonstrating increasing production. Concurrently the environmental costs of these practices are also becoming better understood and this is a critical component for reducing the risk of project failure and in recruiting sponsor support. Project failure seems highly correlated with increasing cultural heterogeneity and land/water/tenure disparity. Socio-economic conditions appear to contribute as much to individual project success as do physical and biological criteria. Economic measures of success between projects is also difficult due to differences in cultural and societal values; however, these variables must be included when assessing implementation risk and benefits. Sustainable enhancements coupled with community based natural resource management are becoming critical components for financial sponsorship. Non-government organisation (NGO) project sponsors are becoming more participatory in the biological and cultural measures of enhancement project success. Cultural obstacles may be more limiting to project success than increasing the biological and political implementation requirements. The scientific community is becoming active in the examination of animal, plant, and genetic introductions. Additionally, the global awareness of the conservation of genetic resources and environmental issues in general, is increasing the responsibility of project implementers. Empirical rules derived from community ecology and the significant amount of data from stocking efforts can underpin some limited predictive enhancement project planning. Negligible trophic interactions created by identification of niche vacancies are important considerations for project success and wider acceptance in the scientific and NGO communities. The predictable integration of candidate enhancement species, most critically those involving introductions in targeted habitats, will benefit production, increase likelihood of securing sponsor and scientific community partnership and reduce project failure.


The present Consultation was convened to review and assess the status of fishery enhancement technology and the socio-economic requirements that are necessary for successful fisheries productivity that meet sustainability criteria for long-term success. Aspects of the sustainability criteria for enhancement effects on the environment including the maintenance of genetic resources and biodiversity were also covered. Participants described projects from Latin America, China, South-east Asia, China, Bangladesh, India, Africa and Australia, which were then examined for trends that might support common goals for implementation.

The meeting was organised thematically to focus on technical, socio-economic and administrative/implementation issues. It was the desire of the hosting agencies that these discussions would elucidate common features that underpin successful enhancement projects and identify gaps in knowledge that constrain success. Additionally, this consultation invited several scientists who would provide insight to expand on various genetic resources issues. Genetic resource management is an increasingly important aspect of enhancement planning and management as biodiversity is inextricably linked to sustainability questions and is a basic premise contained in a precautionary approach as described in the Code of Conduct for Responsible Fisheries.

Successful enhancement implementation requires a convergence of technical and socio-economic variables and must be viewed as a mosaic from which donor agencies and implementing bodies must select information based on previous project data to create planning processes. Enhancement planning should minimise risk and create a framework for the development of project guidelines that are supported by analytically-based models that provide the necessary feedback mechanisms for adaptive management. In this context management strategies will need to respond to the demands of cultural, environmental, and technological pressures. Enhancement project components are not easily assessed nor do they lend themselves to inter-project comparisons due to the variability inherent in cultural and environmental systems. As such, the development of predictive models to support project planning must be viewed conservatively. Donor agencies understandably must place increasingly critical criteria on enhancement projects to maximise the chance of success and minimise the risk of environmental damage.

The cultural heterogeneity representative of the significant differences reflected in the community examples spread across the continents and cultures described in the ECIFE is mirrored by the complexity and environmental heterogeneity found in aquatic systems. These differences pose problems in the evolution of predictive models that can quantitatively express dependable outcomes of interventions.

The prospects for predicting individual project success are further complicated by the such independent variables as the cumulative rate of environmental change within an enhancement watershed (or in some cases wholesale changes within a biome) and the unpredictable forecast of climate change. Coupled with the uncertainties of human behaviour in the control of resources created by an intervention, the strategic planning for enhancements needs to address what deleterious outcomes can be predicted as potential events and thus avoided or at best mitigated.

Risk assessment and the models utilised in environmental risk analysis are widely used in development or mitigation in industrialised societies. However, risk assessment that needs predict change in an ecological setting is in its infancy. This situation is in great part due to the nature of ecological systems and the science of ecology itself. The gaps in knowledge of ecological process are too large, thus the uncertainty factor is too great, to assume that the tools and knowledge exist to dependably quantify enhancement outcomes on the environment. However, some qualitative approaches in risk assessment may provide a vehicle for examining the potential of environmental risks associated with enhancements. Qualitative models may also contribute significantly to the strategic planning process due to the ability for participating institutions to rank, by consensus, the relative severity of undesirable outcomes or losses that may result from an enhancement activity.

This paper suggests a qualitative approach to assessing inland fishery enhancement environmental risks. Borrowing heavily from ecological rules evolving in the biology of invasions the authors propose a precautionary approach to enhancement management that could contribute to the strategic planning process of fishery interventions in low income food deficit countries. This approach is limited to the environmental component of enhancements from a technical standpoint and does not suggest it would work for the institutional constraints which most interventionists would agree are equal to or greater than the technical limitations. However, the process suggested here could contribute significantly to softening the dichotomy that exists between the need to develop food security and the sustainability issues represented in biodiversity concerns and the increasing criticism surrounding environmental manipulation and tension enhancement projects can engender with conservationists.


Fishery enhancements are techniques to intensify the production of aquatic water bodies. Inland fishery enhancements take a variety of forms reflecting increasing investments of effort, capital and habitat manipulation and concern for environment (Fig. 1). In the simplest and most extensive form the harvest of natural production is optimised by increasing the efficiency of natural production through better harvest techniques and sustained through rational fisheries management. Such harvests can be increased by the use of more efficient gears and greater fishing effort that is responding in step to maximum sustainable yields determined by natural factors. Subtle forms of environmental manipulation can increase catch efficiencies in the form of brush parks, artificial reefs and fish gathering devices like ditches.

Increasing intensification measures include manipulation of natural biological factors such as recruitment by regular stocking of juvenile fish from hatchery sources or creating self-reproducing populations and introductions of non-native fish species. Well-capitalised enhancement projects will frequently include some form of habitat manipulation in attempts to improve production. These can include improvement of fish migration corridors, creation or protection of fish spawning habitat, and fencing to limit escapement of target species.

At these increasing levels of intensification anthropogenic shifts in community structure can occur with the removal of predators. More intensive interventions lead to higher levels of control of natural factors that can be described as aquaculture and include fertilisation of water bodies to enhance primary production, feeding, genetic modifications, stocking and cage culture.

The most controversial enhancements are introductions of non-native fishes. Introductions of new species are done for a variety of reasons but the most frequent' justification is to improve the existing or to create new fisheries. The introduction of non-native species has been a focal point of criticism in the scientific literature and more recently in the popular development press.

Figure 1. Intensification of production.

Figure 1.

Probably the most visible and controversial example of an introduction that has mobilised the scientific community into examining introductions as a science and policy has been the introduction of the Nile perch into Lake Victoria that was initiated in the early 1950s. The trophic cascade of the Lake Victoria system described in the early 1990s (Kaufman, 1992) alerted scientists and development institutions to the magnitude of change that can result from the introduction of a piscivorous predatory fish into a species-rich environment. Additionally, the change that can occur from an introduction is not limited to the aquatic system. The Lake Victoria situation created perturbations in the upland system when forests were harvested to smoke the perch (Reynolds et al., 1995). These problems were compounded by the value of the new resource and the new gear required to fish the perch when mechanised vessels were introduced to the local economy. The full picture is obscured by the total number of anthropogenic factors that began with British colonisation and continued with the introduction of tilapias concurrently with the Nile perch. Coupled with habitat destruction and the natural variation of climate the Nile perch was only one factor in a host of changes to the system. In recent descriptions of the Lake Victoria Nile perch introduction the environmental and development press has often obscured the problems with oversimplification of the problem (i.e. not accounting for the complexity of the system) and overstating the Nile perch as the primary source of the problems in Lake Victoria (Kaufman, personal communication). There are a number of other examples of recently published books (Brown et al., 1996; Brown and Kane, 1995; Cohen, 1995) describing the status of world population and global resource limitations and impacts to biodiversity that overstate specific impacts to genetic resources by introductions or fishery situations. Although authoritative works in themselves perceptual problems arise when scientific data relating earlier work on introductions is recited without the present context of interpretation that benefits from the current science of introductions and biological conservation.

This situation where the perceived and actual problems are not distinguished by the members of the development and environmental communities is contributing to the difficulty of assessing enhancement potentials. Indeed this point of perceived versus actual problems when examining environmental conditions was a conclusion of consensus resulting from the ECIFE.


Although the debate of the Lake Victoria system still rages the hindsight perspective is evolving along with a new awareness of the complexity of aquatic ecosystems. Concurrently the science of biological invasions has matured so that particular trends may assist the interpretation of enhancement risks. Complementing these developments fishery scientists working on the impacts of cultured fish on the environment have created a multidisciplinary approach to risk assessment that places the conservation of genetic resources as the critical element underpinning of the potential loss associated with the risks of introductions.

In a recently published report of a workshop on invasion biology Moyle and Light (1996) propose a set of rules based on empirical studies that address the dynamic nature of aquatic systems. By stressing the role of environmental variability in determining the outcome of invasions they provide a conceptual model of aquatic invasions that could benefit the approach to establishing a process framework for dealing with the uncertainty in enhancement strategic planning.

Moyle and Light's empirical rules borrow from community ecology assembly theory the idea that communities are constructed over time by processes of successive invasions and extirpations. This model also builds on Vermeij's (Vermeij, 1996) work that depicts invasions as being defined as three basic phases of arrival, establishment and integration. Vermeij's model provides a temporal framework that allows enhancement planning specific windows in which projects can monitor successive events of community development after the introduction of a species or a particular stock that may be distinct by genetic modification.

Adding Moyle and Light's approach of empirical rules to strategic planning for enhancements the planning framework can then be amplified by a background situational context that can be applied to environmental situations appropriate to the specific set of conditions reflecting a particular enhancement. Moyle and Light's rules are also appropriate to many enhancement situations because they include classifications of fishes by trophic groups and the relative level of disturbance of the receiving habitat. By incorporating the relative level of disturbance this model increases its appropriateness for enhancement planning since many areas targeted for enhancements are under intense population pressures and experiencing relatively high levels of human disturbance.

The strategic planning for enhancements needs to consider the following:

The planning approach described above can be further assisted by the use of risk assessment models being proposed by fish geneticists who examine the effects of supplementation efforts on the environment. The invasion models proposed by Moyle and Light can converge with the risk assessment models, further drawing on the strengths in the scientific community that can prove useful in integrated approach to enhancement implementation.


The development community faces a number of challenges in meeting the goals of increasing fish enhancements in low income food deficit countries. Recruiting confidence in the scientific and environmental communities is an important goal as is meeting the criteria of donor organisations that like the development community are also responding to the demands created by the needs to sustain biodiversity. It is difficult to respond to these challenges precisely because of the uncertainty inherent in ecological processes. The dynamic nature of aquatic systems and the variability in community structure make predictive models elusive. However, there is logic in applying qualitative models to issues of uncertainty if the risk of loss can be described.

Qualitative models are an appropriate application to enhancement planning due to the enormous uncertainties that cannot be described. The ECIFE provided discussion that once an enhancement is underway or even being observed by neighbouring communities, further manipulations by society members are likely and uncontrollable. Further complicating matters is the unprecedented rate of change that accompanies exponential population growth and the effect that these populations have on the environment including those that may be targeted for enhancement. The attractiveness of models that rank risk of loss without assumption that independent variables can be quantified increases enormously. Add to this the uncertainty posed by climate change, then qualitative models appear not only reasonable but inevitable in terms of their appropriateness.

The effect of artificial propagation of fish on the environment has been receiving increasing attention in recent years especially by biologists in the United States who are responding to stringent federal laws dealing with endangered species. In this context the effect of hatchery fish on wild stocks has required new approaches in the examination looking at genetic change. Biologists (Currens and Busack, 1995; Waples, personal communication) have proposed utilising fairly simple models that relate vulnerability to risk and hazard (loss) in the equation V=RxL. This risk-benefit analysis fits qualitative models since the risk that accompanies an enhancement can be plotted against the increasing loss. It would also be appropriate in enhancement planning to plot the relative vulnerability of risks associated with the vulnerability posed by disturbance levels like those described by Moyle and Light that increase the opportunities for certain classes of introductions (Fig. 2).

Figure 2. A hypothetical qualitative model of risk assessment showing potential relationships of various enhancement outcomes in response to different enhancement technologies and in response to various levels of habitat disturbance.

Figure 2.

In a recent (US National Research Council, 1996) US National Academy publication on policy and risk analysis several key recommendations were forthcoming regarding the underlying assumptions that must be made when developing risk assessments. Included in these objectives were the requirements that the science must be right in the context that high scientific standards must govern the analytical methods and the treatment of uncertainty. Additionally, the analysis must address the specific concerns of affected parties and the concerns must include socio-economic as well as ecological risk factors.

The process outlined above that merges the technical requirements of enhancements with the policy concerns of donor agencies and countries will create an opportunity to bring together the sometimes opposing forces that have worked against enhancement success.

Consistent with the call for increasing scientific rigor in environmental risk assessment models, the collaboration of ecologists working in the field of invasion biology can reduce the tension in the food security-conservation dichotomy. The process described here addresses some of the specific concerns, such as the lack of a precautionary approach, of scientists critical of enhancements. The development of models incorporating risk and vulnerability to rank losses associated with enhancement outcomes is supportive of the conclusions reached by consensus in the ECIFE, the Precautionary Approach to Responsible Fisheries, and evolving criteria of donor organisations and countries.


Brown. L. et al. 1996. State of the World 1996. Worldwatch Institute.

Brown, L. and H. Kane. 1995. Full House. Worldwatch Institute.

Cohen, J. 1995. How Many People Can The World Support?.

Currens, K. and C. Busack. 1995. A framework for assessing genetic variability. Fisheries 20(12): 24–31.

Kaufman, L. 1992. Catastrophic change in species-rich freshwater ecosystems: the lessons of Lake Victoria. Bioscience 42(11): 846–858.

Moyle, P. and T. Light. 1996. Biological invasions of freshwater: empirical rules and assembly theory. Biological Conservation 78: 149–161.

National Research Council. 1996. Understanding Risk: Informing Decisions in a Democratic Society. National Academy Press. 264p.

Reynolds, E.J., D.F. Gréboval and P. Mannini. 1995. Thirty years on: the development of the Nile perch fishery in Lake Victoria. In: The Impact of Species Changes in African Lakes (Pitcher, T.J. and P.J.B. Hart, eds.). Chapman & Hall, London. 601p.

Vermeij, G. 1996. An agenda for invasion biology. Biological Conservation 78: 3–9.

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