Some Studies on Crayfish Distribution in a Small Pond

While trapping crayfish of the species Orconectes virilis Hagen (formerly Cambarus virilis Hagen; Hobbs, 1942) during the summer of 1956 in a small pond in Lincoln, Massachusetts, it was noted that certain sites within the pond yielded more crayfish than others. Also it was noted that the catches varied from time to time throughout the summer. These observations prompted speculations about the preference of the crayfish for certain sites in the pond, possible migration, and their population density. Therefore, it was decided to plan the trapping activities for the summer of 1957 to include a study of some of these problems. METHOD The site of the study was an overflow basin of the Hobbs Brook Reservoir in Lincoln, Massachusetts. Physically the basin approximates a rectangle about 180 m long in the east-west direction and about 45 m wide in the north-south direction. The average depth of the water is about 1.5 m when filled. The water level fell from about 0.5 m below normal level at the beginning to about 0.9 m below normal by the end of the experiments. The east and west ends are lined with large rocks which normally extend under the surface of the water. The sides are lined with gravel, the bottom of the soutlh side being muddy in comparison to the somewhat more sandy bottom of the north side. Three stations were used in the studies. Station A was located in the middle of the east end (Fig. 1). Station B was located on the north side about 38 m west of the east end. Station C was similarly located on the south side, directly across from Station B. Crayfish were trapped, marked, and released at these three stations. Minnow traps baited with fish trimmings were used to trap the crayfish. Haddock heads seemed to be the most effective bait. Salmon and haddock backs were less effective and mackerel - heads least of all. The traps were placed approximately 7 to 8 m off shore at each station within a radius of about 2 m. Four experiments were carried out (TABLE I). In Experiment I the animals were trapped at Station A and released at Stations B and C. In Experiment II the