Upstream Movement of Crayfish in an Intermittent Oklahoma Stream

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Abstract
Weekly observations were made on a population of the crayfish, Orconectes nais, in an intermittent Oklahoma stream. The population density at the beginning of the study was about 1 crayfish for every 2 ft2 of stream bottom. The percentage of young-of-the- year crayfish in the total population increased as the summer progressed, indicating extensive mortality inolder individuals. The life span of this crayfish is two years; thus it has a rapid population turnover rate. Migration of crayfish between three adjacent sections of the stream stopped when the falling water level isolated the sections from each other. The general pattern of migration was upstream. Physical and chemical conditions of the water were approximately the same for all sections. Crayfish migrated extensively upstream from a section with a silty substrate toward one with a rubble substrate. In contrast, upstream migration from a section with a rubble substrate into one with a silty bottom was much less pronounced. Drought obliterated the population that had migrated upstream into the rubble-bottomed pond. Thus survival in such extremely fluctuating habitats seems to be a matter of chance. Periodic floods tend to sweep crayfish downstream; perhaps their upstream migration acts as a compensating redistribution mechanism.

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