LIFE HISTORY OF THE BLUE CRAB. 401 



Within the larger bodies of water the crabs are quite generally dis- 

 tributed — that is to sa}', individuals are not uncommon auN^where, but 

 there are certain localities Avhere their abundance is almost incredible 

 and the suppl}" seems inexhaustible. These favored spots seem to be 

 the mud bottoms such as arc to be found near the mouths of the larger 

 rivers, in shallow water where there is an abundance of vegetation. 

 Hard bottoms, oyster beds, or bottoms consisting of soft ooze without 

 vegetation are apparently not best suited to their welfare, for on such 

 spots comparatively few crabs are to be found. 



The habitat varies considerably with the season. In the summer 

 the craljs live close to the shore; in the winter they move into deeper 

 water. It would also seem that the habitat varies somewhat with the 

 age and sex of the individuals, for even in the summer the small and 

 medium sized crabs are most abundant in shallow water, while the 

 large males remain in the deeper channels.'^ An examination of the 

 cral)s from shallow water shows that small males and virgin females 

 constitute the bulk of the catch. 



POWER OF MOVEMENT. 



Either in the water or on land the blue crab is an animal of great 

 activity and has considerable power of endurance. Progression 

 through the water is effected by means of a sculling motion of the 

 broad, oar-like posterior legs, and under ordinary conditions is slow, 

 the effort of the animal being apparentl}^ only to keep itself afloat 

 while it is borne along by the current. Under these conditions the 

 movement is either backward or sidewise. The shell is held with the 

 posterior portion uppermost, the legs are brought together above the 

 back and strike backward and downward at the rate of from 20 to -10 

 strokes per minute. When alarmed, however, the animal strikes out 

 with great vigor and rapidity, moving its paddles too swiftly for the eye 

 to follow; it moves through the water almost as rapidh" as a fish and 

 quickly sinks below the surface. When on the bottom and undis- 

 turbed, the crab ma}- be seen to walk slowly about on the tips of the 

 second, third, and fourth pairs of legs, the large pincers being held 

 either extended or folded close under the shell and the paddles either 

 raised and resting against the back of the shell or assisting the move- 

 ment by slow sculling strokes. In such cases the movement is in any 

 direction — forward, backward, or sidewise — although the usual direc- 

 tion is sidewise. If the animal becomes alarmed it moves away by a 

 combination of the walking and swimming motions and often disap- 

 pears like a flash. In fact, so rapid is the movement that it is almost 

 impossible to see how it is accomplished. It is too steady and uniform 



"This fact is well known to the fishermen, who frequently refer to these large males 

 as " channellers." 



F. C. 1904—26 



