10 PROCEEDINGS OF THE NATIONAL MUSEUM V0L - ™ 



viduals of Cambarus I. longulus in a given riffle area in January than 

 in April. Utilizing the usual collecting techniques, however, it is 

 very difficult to obtain even a dozen specimens during the winter 

 months; in the early spring the collectable individuals are mostly 

 males and yearling females ; a little later in the spring the adult females 

 appear in the population so that an approximation of the population 

 size cannot be obtained until late spring. In late fall the population 

 begins to diminish in size and by winter it has almost disappeared. 

 This fluctuation is obviously a result of the habits of the species in 

 burrowing below the frostline before the stream freezes and, although 

 the males and yearling females emerge in early spring, the adult 

 females remain in the burrows until their eggs (laid in late winter or 

 early spring) have hatched and the young have left or are ready to 

 leave their mothers. Although year-round data are not available 

 on any of the crayfishes in the Mountain Lake area, Smart (1962) 

 and one of us (Hobbs) have not observed appreciable changes in 

 populations in Swift Run in Greene County, Va., over a 10-year 

 period. 



In contrast to the seasonal fluctuation of populations of C. I. 

 longulus, the collectable population of C. sciotensis in Sinking Creek 

 exhibits little fluctuation throughout the year and from year to year, 

 and the same is true for many populations of C. b. bartonii. 



Adequate data are not available to assess the population sizes in 

 various localities, but possible effects of competition are emphasized 

 in (1) the natural experiment in Little Stony Creek above the Cas- 

 cades, which C. sciotensis has not been able to ascend (here, without 

 competition, C. b. bartonii occurs in much larger numbers than in 

 similar streams where it occurs with C. sciotensis) , and in (2) Mountain 

 Lake, where the introduced 0. juvenilis has displaced the introduced 

 C. acuminatum and the native C. b. bartonii (Hobbs and Walton, 1966a). 



Perhaps the most exciting observations of competition between 

 species in the area are those that are in progress in Potts Creek. In 

 1960, two of us (Hobbs and Walton), together with several others 

 whose help has been acknowledged above, visited station 7 and within 

 a few minutes collected 12 specimens of C. b. bartonii, 10 of C. I. 

 longulus, and 12 of 0. juvenilis. In 1965, one of us (Walton) returned 

 to this locality and this time collected 94 specimens of 0. juvenilis and 

 a single specimen of C. b. bartonii; not one individual of C. I. longulus 

 was to be found! There is no record of 0. juvenilis having been 

 intentionally introduced into the headwaters of Potts Creek and 

 presumably fishermen collecting their "crawfish bait" in West Virginia 

 released excess animals in the creek, thus stocking a population that 

 not only has become successfully established but is in the process of 

 replacing the native species as it has done in Mountain Lake. In an 



