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ce 8) n- ~e ie ~e a- i ). ry :n b- of 1- ~d n a, r •s i- Y ;t .r Direct Control of Fauna hazard that comes with intentional use of hatchery fish from inappropriate gene pools. In Norwegian rivers, farmed Atlantic salmon (Salmo salQr) are threatening native fish through cross- breeding of wild with farmed fish, with the sub- sequent risk of losing genetic material essential for the survival of local populations (Gausen & Moen 1991 ~. The river catchment manager must always be awaze of this kind of threat. The dangers inherent in introductions are further enhanced by the blind faith put in recent genetic 'breakthroughs' where managers were made to believe large populations of desexed fish established by stocking would never produce off- spring. An excellent example of this fallacious assumption was the release of reportedly sterile) grass carp (Ctenopharyngodon idella) into the Mississippi River and the subsequent colonization of the system as naturally-reproduced popu- lations established rapidly (Brown & Coon 1991), all of this despite caution advised by scientists well-placed to predict ecological disasters. Effect of environmental contaminants Residues of persistent, toxic substances that bio- accumulate have been linked to the reproductive failures of wildlife (e.g. bald eagle Haliaeetus leucocephalus) and fish (e.g. lake trout Salvelinus naymaycush). Obviously the body burden carried by any hatchery fish and the potential to accumu- late more in the environment into which it has been introduced must be considered as factors affecting the overall success of fish survival and growth. It is possible that mega fish stocking pro- grammes will fail to re-establish self-sustaining fish populations in rivers because of uncontrolled toxic effluents and high concentrations of con- taminated sediment (Gilbertson 1992). One pertinent criterion often ignored by man- agers is whether or not the species chosen for a river fish culture programme has the properisity to accumulate persistent toxic substances that may threaten human health. Notwithstanding any effects that biomagnified toxic body burdens may have on the general health of the carriers and on the specific reproductability of mature fish, there is the fundamental issue of effects from toxic substances in fish on humans, especially 397 women and children. Swain (1988) identified sig- nificantly damaging effects on maternal health and showed the risks associated with trans- placental transmission to infants in utero and for nursing infants. 20.4 ROLE OF REGULATIONS Regulations are an important mechanism for controlling risks to native fish communities which may result from stocking-related activities. Regulations can be used directly to control the choice of species or strains used for stocking, including the use of exotics, or to prevent the introduction or spread of serious fish disease agents. Indirectly, regulations play a major role in con- tributing to the success of a stocking programme. Fishing seasons and access can be controlled to protect stocked fish when they are most vulner- able, such as at the stocking site, or in the case where anadromous species aze stocked in a river as pre-smolts, prior to their movement down- stream to a lacustrine environment. More funda- mental regulations controlling exploitation can be used to eliminate the need for starting a stock- ing programme. Regulations are needed to provide protection at continental, regional or local levels. Man-made boundaries ~i.e. national, territorial or local govern- ment) are the main mechanism used to develop, implement and enforce regulations. The fact that fish do not recognize man-made boundaries poses a major challenge to the effectiveness of regula- tions. For this reason, international commissions such as the North Atlantic Salmon Conservation Organization, EIFAC and the Great Lakes Fishery Commission play an important role in developing international agreements and co-ordinated strategies which assist in managing large watersheds. National or territorial controls provide the ma- jor framework for implementing legislation, re- gulations and policy. These controls are often easier to enforce, because they aze based on clearly defined boundaries. Territorial legislation can be used as the basis for regulations which control at the local level, such as specifying the location of fish sanctuaries.