Oceanic or coastal spawning grounds of fish are often distant from nursery areas. Fish larvae require appropriate currents and sufficient and suitable food during transit to reach the nursery area at the proper time, size, and condition. Meteorologic and oceanographic factors influence food availability and transport direction and time. Annual variation in these controlling factors could affect recruitment success. Certain generalizations can be made that apply to marine and estuarine systems. Reproduction occurs in a selected portion of the species' total range. Spawning often takes place close to gyral, upwelling, or other directional circulations that frequently are associated with major current systems. The coupling of spawning to natural oceanographic transport systems for eggs and larvae is advantageous to a species as long as those systems operate normally. The details of such coupling, and the consequences for eggs and larvae of deviations from usual transport mechanisms, remain poorly understood. Investigation of year-class success requires a clearer understanding of the natural variability and periodicity inherent in these physical processes. Further research is needed to resolve these details, including environmental cues to reproductive behavior and relative importance of passive and behaviorally mediated transport; to statistically analyze atmospheric and oceanographic cycles; and to quantify transport mechanisms for spawner-recruit models and predictions of year-class success.
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