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') . I;, that temporary pooling of water at the mouth of the Little Colorado River during daily hydropower peaks of darn discharges often created a habitat conducive to larval and juvenile fish. During the descending limb of the daily peak, water in the pool would be pulled into the mainstem carrying (or entraining) the larval and juvenile fish. In this example. the larval and juvenile fish descended from the Little Colorado River. During the high-discharge event similar pools will be available at the mouths of many tributaries but the source oflarval and juvenile fish may, in most cases, be from the mainstem. The ability of these life-history stages to move into such refuges as opposed to being swept downstream will be tested. Metbods Downstream displacement of (I) larval and (2) juvenile fishes will be studied automatically for the former by thorough analysis of pre-flood, flood, and post-flood particulate drift. A need for additional, more specific studies of potential displacement of eggs and larvae is not anticipated, but the following suggestions for this aspect of the experiment may result in other kinds of data becoming available, (28) One danger influencing interpretation of apparent drift of eggs and larvae is that adults may respond to the event by spawning in response to (I) stabilization of discharge for the period prior to upramping; (2) increased discharge or rlring and stabilization of flow during the event; (3) as a response to the descending limb of the hydrograph, or (4) respond to the event by spawning somewhere else than in the mainstem, with the eggs or larvae entering the mainstem in some way. Whether or not eggs or larvae appear in drift samples will depend upon (1) whether or not eggs and larvae are present in the system (have adults spawned yet?); (2) fragility of eggs and larvae (if extremely fragile or handled roughly they may be reduced to amorphous, gelatinous masses and therefore undetected); (3) hatching time of eggs deposited during one or more of the above periods (in cold water of the mainstem, hatching time will likely exceed 10 days for any species present; it may be longer, but likely not shorter); and (4) at what point in the scenario larvae or eggs deposned other than in the mainstem (e.g., in creek mouths, which is a possibility) are entrained into the channel to become susceptible to drift netting. Sampling for eggs and larvae in tribuwy mouths should be done (at the same time as adults and subadults are sampled to test Hypothrsis 1, above) in order to cover the eventua1ity that tributary inputs may influence mainstem drift. Hypothrsis 2 would be rejected for larval fishes if changes in larval drift (which are not attributable to one or more of the potentially confounding circumstances given above) are undetectable throughout the period of the experiment This assumes that eggs or larvae are even present during the period of study. which they will likely be based on other years of information. (2b) Assessment of the presence or absence of downstream displacement of juvenile fishes may be possible by exhaustive sampling (adequate to obtain statistically comparable sarnples) by seining along 5-10 selected sandbars or by electrofishing along 5-10 selected, talus- dominated shorelines (e,g,. Valdez 1993 techniques). Pre-, during, and post-flood data can thus be placed in perspective. Hypothrsis 2 would be rejected for juvenile fishes if there are (I) no statistically significant changes in the population sIZes or (2) if the post-flood pattern is other than an apparent upstream depletion and downstream accrual in population sizes. The evidence 24