Seasonal Activity, Migration and Distribution of the Crayfish, Pacifastacus Ieniusculus, in Lake Tahoe

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Abstract
Investigation of the natural history and ecology of the crayfish, P. leniusculus, in Lake Tahoe [California, Nevada, USA] revealed extensive seasonal migration. A series of trap lines was set to determine patterns and possible causes of seasonal migration. During summer and autumn, the peak bathymetric distribution of crayfish was in shallow, near-shore waters. In autumn, with decreases in both water temperature and daily solar radiation, the adult population migrated into deeper waters. This migration is probably an adaptation of the species to avoid winter storms that cause high rates of mortality among members of the population remaining in shallow water. As is typical with many other invertebrates living in an environment with large temperature variation. P. leniusculus shows peak activity during the warmer summer season and very low activity during the winter months. Diel activity was directly related to the length of the dark interval with even a small amount of light (e.g., moonlight) reducing the activity period of the population.

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