J.M. Kapetsky and U. Barg, Fishery Resources Division,
FAO, Rome, Italy
This paper provides a short overview of kinds and characteristics of quality and quantity indicators for inland fisheries and aquaculture and shows how they relate to indicators in other sectors.
FAO OBJECTIVES FOR INLAND FISHERIES AND AQUACULTURE
Indicators have to be viewed in the context of FAO's objectives for inland fisheries and aquaculture. These, very broadly, are to sustain a productive environment for fisheries and for the further development and expansion of aquaculture.
Fairly simple indicators (Table 1) can be interpreted together to reveal the status of fisheries and of fishery resources. For example, artisanal fisheries usually provide from 1 to 2 t/person/year. If the catch per fisher is significantly less, the resources are likely to be over-exploited or the aquatic system is poor in its fish production potential, either naturally or because of human-induced changes. If one directly observes, or has the data to hand to show that gear has been purchased or constructed to catch relatively small fishes and if catch data confirm that mainly juvenile fishes are being harvested, then one can conclude that the resources are being very heavily exploited.
Water Quantity as an Indicator of Fishery Potential
Water quantity is a very important indicator of fishery potential, and its variations are indicative of natural or human-induced changes in fishery potential. For example, about 57% of Africa's large water bodies vary seasonally and inter-annually in their surface area: river floodplains, swamps, shallow lakes and reservoirs (Kapetsky, 1995). Similarly, variations in flows affect both the efficiency of fishing and fishery biological productivity. Models have been developed to predict fishery yields one and two years ahead based on changes in water availability (Welcomme, 1985) and remote sensing technologies are being developed to periodically and cheaply measure variations in water surface area in inland systems for predictive purposes (e.g., Travaglia, Kapetsky and Righini, 1995).
Indicators of the "Health" of the Aquatic System
Usually this type of indicator is quantitative in nature and the basic concepts are covered in limnology textbooks while the techniques are in standard texts on water quality measurement (Wetzel, 1975; Alabaster and Lloyd, 1982; APHA, 1989; Chapman, 1992; Hellawell, 1986; Howells, 1994). However, there is a very simple qualitative indicator of ecosystem health: the kinds of fish species present. Generally, the greater the variety, the better the condition of the system in terms of long-term stability.
A few key physical and chemical measurements go far toward indicating the status of the aquatic ecosystem: dissolved oxygen, turbidity and electrical conductivity.
In short, the dissolved oxygen concentration indicates the capability of the water body to support aquatic life, turbidity indicates opportunities for photosynthesis and conductivity (in non-saline waters) discloses the system's richness in nutrients.
Of course, other indicators are routinely used and some require sophisticated and costly equipment for data collection and analysis. The choice of additional indicators will depend on requirements to measure perceived changes in a given water body which may be affected by different types of pollution or physical degradation (Barg et al., in press; Dunn, 1989; Muller and Lloyd, 1994). For example, the productivity of an aquatic system may be impacted by siltation, or very low concentrations of heavy metals or pesticide residues. Use of the key indicators above would point to a problem. This would have to be identified by additional measurements.
KEY AQUACULTURE INDICATORS
Aquaculture indicators (Table 2) function to measure the suitability of the environment for aquaculture development and, when measurements are made periodically, many of the same parameters are important gauges to judge the sustainability of aquaculture. In employing them, one is matching a culture system (e.g., a pond) and an organism (e.g., a carp or tilapia) to an environment (e.g., family farm or commercial fish farm).
¤ water availability (and water balance)
The significance of these general indicators is mainly self-evident - they pertain very closely to agriculture development and management. An example of how information created for agriculture can be re-interpreted to assess aquaculture potential at a continental scale is given by Kapetsky (1994).
Among the aquaculture indicators, land use and land cover merit special mention. These can be interpreted for a variety of decisions including those on relative amount of land cover types as they influence water quality, crop types and agricultural by-products as fish feed inputs, and land availability, land acquisition and land preparation costs (e.g., Kapetsky, McGregor and Nanne, 1987).
INDICATOR DATA PROBLEMS
In the realm of indicators for inland fisheries, the necessary data often are not collected for individual water bodies, except the largest ones. Water quality indicators frequently are not synoptic and there can be problems of differing methodologies for the same parameter. Water quantity indicators may not be in useful units of measurement (e.g., water volume in place of water surface). Indicators for all purposes suffer from sporadic and or geographically incomplete coverage.
¤ The indicators covered in this paper can be useful for a range of purposes. They may be employed for brief visits to individual sites, or they may be used for geographically broad, long-term studies. Remote sensing can be an important tool for data acquisition for the latter and geographical information systems are increasingly used to evaluate the indicators when taken together.
¤ Generally, indicators useful in other sectors, notably agriculture, can be used directly, or re-interpreted, for fishery and aquaculture purposes by selecting different thresholds.
¤ For inland fishery resources and for aquaculture, key water indicators can be relatively simple, but they have to be dynamic (i.e., measured frequently).
¤ Frequency of observation should take into account seasonality and the rate or frequency of land and water use changes in the river or lake basin.
¤ Water quantity or surface area is a vital indicator for fisheries and aquaculture.
¤ Land cover (or better, land use) is a key land indicator from which much can be inferred about water quality and availability of land and water for fisheries and aquaculture.
¤ More sophisticated indicators can be useful, but continuity of coverage over large areas with simple indicators is more useful than geographically and temporally spotty coverage.
Alabaster, J.S. and Lloyd, R. 1982. Water Quality Criteria for Freshwater Fish. FAO and Butterworths, London. 361 p.
APHA [American Public Health Association]. 1989. Standard Methods for the Examination of Water and Wastewater. Washington D.C. 1268 p.
Barg, U., Dunn, I., Petr, T. and Welcomme, R.L. in press. Inland fisheries and water management. In: Handbook of Water Resources and the Environment, A.K. Biswas (ed.). International Journal of Water Resource Development, Oxford, UK.
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Müller, R. and Lloyd, R. (eds.). 1994. Sublethal and Chronic Effects of Pollutants on Freshwater Fish. FAO and Fishing News Books, Oxford, UK. 371 p.
Travaglia, C., Kapetsky, J.M. and Righini, G. 1995. Monitoring wetlands for fisheries by NOAA AVHRR LAC thermal data. Environmental Information Management Unit, Sustainable Development Department, FAO, Rome. RSC Series 68. 30 p.
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