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E. Fish stock enhancement

The restoration of water quality in streams should consider not only the physical attributes of the running water environment, but also the biotic features. Fish are not only an important component of the riverine biotic community but also have an important socio-economic and aesthetic value. Fish and fisheries issues often provide a useful tool for creating an increased level of public environmental awareness. Public acceptance of the importance of stream systems as living resources is the only way to effectively restore the integrity of the stream system and ensuring the proper functioning of its biological processes, including its self- purification abilities. Public awareness, therefore, is a critical element in achieving the sustainability of river ecosystems at the watershed scale.

The enhancement of a river fishery the translocation of fishes has a long history. However, there is still no certainty as to the result of such actions. The success of stocking is dependent on planning. The objective for translocating living resources must be stated at the outset using clearly defined terminology to avoid any misunderstanding. Some definitions of commonly used terms have been adopted by EIFAC (Welcomme 1998) and are presented herein. In addition, stocking and introductions should be based upon an agreed action policy (Cowx 1998, Welcomme 1998, Lorenzen and Welcomme 2001).

Definitions

• Introduction - the intentional or accidental transport and release of species into the environment outside of their present range by humans;
• Transfer - the movement of individuals of a species or population, intentionally or accidentally, within their present range;
• Stocking - the repeated introduction of native or exotic species of fishes into a natural ecosystem from external one.

Typical motives for stocking

• Mitigation (Compensation) - stocking is used to replace fishes lost from the natural population because of a disturbance to the environment by human activities that modify habitat (loss of spawning grounds) or disturb migration (dam construction). It usually relates to native species and, ultimately, results in normal recruitment.
• Maintenance - stocking is used to supplement recruitment in cases of overfishing. Changes in fishery exploitation management and regulations are a form of maintenance.
• Enhancement - stocking is used to maintain fisheries productivity at the highest possible level in situations where the carrying capacity of a water body is greater than the observed population. This situation can arise due to a shortage of spawning grounds, for example.
• Conservation(Restoration) - stocking is used to re-establish stocks of a species threatened with extinction. This kind of stocking should be temporary and involve a more active management strategy for the aquatic ecosystem to create self-sustaining fish populations.

General reasons for introductions

• Creation of new fisheries - stocking is used to establish new stocks of fishes not currently present in the system because of natural barriers to migration or evolutionary isolation. Introductions are usually of fishes with significant trophy or sporting value.
• Filling a vacant niche - stocking is used to supplement the native fish fauna when the native fish fauna do not fully utilise the available trophic and spatial resources. (Note: This is a controversial method.)

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