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Northcote, T. G. (1998). Migratory behaviour of fish and its significance to movement through riverine fish passage facilities. Pages 3-18 in M. Jungwirth, S. Schmultz and S. Weiss, eds. Fish Migration and Fish Bypasses, Fishing News Books, Vienna (Austria).

Migration - movements involving regular cyclic alternation between different habitats used for spawning, feeding, or survival is a common behavioural phenomenon in the Old and New World as well as antipodal freshwater fish faunas. Usually it involves, at some stage in the life cycle, both upstream and downstream movements to reach the appropriate habitats. Upstream phases of migration are active with high energy demands and are directed by a variety of cues, whereas downstream phases often but not always occur by passive drift. Cyclic patterns of movement in such migrations are generally linked to seasonal environmental changes, in concert with the hormonal stage of the individuals involved, but they may be overlaid by did fluctuations. These features of migration are discussed in detail, with specific examples of the migratory capabilities and requirements of various species. Also discussed is the relevance of life-history stages to problems of fish passage over dams, weirs and other man-made obstructions in river channels. Of nearly 200 European fleshwater fish species, 67 are now considered to be threatened by a variety of human activities and major causes have been identified for 48 of these. Over half of these causes are associated with obstructions to migration pathways at dams and weirs, or other alterations in river channel features. There can be little doubt that migratory passageway problems are threatening a high proportion of European fleshwater fishes. Similar conditions are shown to affect many North and South American species, as well as those in the antipodes. If a major loss of freshwater fish biodiversity is to be avoided, more information must be gained rapidly on the migratory behaviour of freshwater fishes, and on effective means to facilitate the passage of young and adults in both upstream and downstream directions. Furthermore, attention must also be given to ensuring that appropriate habitat conditions for spawning, feeding and survival are available at either end of the migratory passageways used.