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<br />INTRODUC'fiON <br />Recruitment is central to population ecology because the abundance of young <br />individuals often drives dynamics of subsequent life stages (Roughgarden et al. 1988). <br />Understanding mechanisms that regulate recruitment is challenging because it integrates <br />many disparate life-history processes, including timing and success of reproduction and <br />growth and dispersal of young. Moreover, most aquatic organisms with larval and adult <br />phases have highly variable recruitment because their high fecundity, coupled with small <br />variations in regulating processes, cause large differences in survival of larvae (Hjort <br />1914, Thorson 1950, Fogarty et al. 1991). <br />Recruitment may often be regulated by interacting physical and biological <br />processes, which change in relative importance across temporal and spatial scales. In <br />marine systems and freshwater lakes, physical processes such as nearshore currents <br />produced by wind may transport larvae into or away from suitable habitats and thereby <br />influence local or regional recruitment (Frank and Leggett 1981, Roughgarden et al. <br />1988). In rivers, regimes of discharge, temperature, and sediment transport influence <br />timing of reproduction by adults and the quality and quantity of critical habitat for larvae <br />(Petts 1984). Distribution, abundance, and size-structure of the population of <br />reproducing adults determines the supply of larvae upon which other biological factors <br />act (Thorson 1950, Gaines et al. 1985, Underwood and Fairweather 1989). These factors <br />