Abstract

Use of SCUBA has made it possible to sample effectively all components of the crayfish population in Trout Lake (Vilas county, Wisconsin) to depths of 15m, Differences in certain aspects of life history and distribution of Orconectes propinquus (Girard) were correlated with differences in temperature which resulted from thermal stratification. For example, although adult females were abundant to 10m during June, the maximum number bearing eggs in the deeper, colder water was 14%, compared to 86% in the shallower, warmer water. More importantly, newly hatched young-of-year occurred almost exclusively in shallow water « 3m), possibly because deep water females molted before their eggs hatched. The distribution of the young then shifted as the season progressed, so that by November the number/m2 was nearly equal at all depths to 10m. Summer molts of adult males, which occurred in late June and early August, were delayed a bout 8-10 days in deeper water; this difference was probably at least partly related to differences in temperature. By mid-August the thermocline represented a sharp boundary at 11-13 m, above which crayfish were abundant (~13/m2 exclusive of young-of-year) and below which crayfish were sparse (~0.9/m2). As the thermocline moved deeper in the fall, however, the distribution shifted and adult crayfish became numerous as deep as 15m.

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