LIFE HISTORY OF THE BLUE CRAB. 113 
crabs have become active and have left the deeper waters, being abundant in the 
shallower waters. The peak of the spring catch is attained then. The falling off in 
the abundance of crabs during August is probably due to two factors; first, a great number 
have been caught by the crabbers; second, many of the females which spawn in June 
and July do so for the last time and die shortly thereafter. ‘This matter is discussed 
more fully on page 123. The sudden abundance of crabs appearing in October and 
November is due to the migration to these waters of the crabs which have matured 
and mated in more northerly waters. These constitute the school crabs previously 
mentioned. About 80 per cent of the individuals of these schools are females, and 
nearly all are adults. 
Third. During the first part of the summer great numbers of sponge-bearing crabs 
are found in the southern part of the Bay. So we have these conditions: A great number 
of maturing females in Maryland which mate and go somewhere else, since no sponge- 
bearing crabs are found there, a sudden appearance of large schools of female crabs in 
the southern part of the Bay in October, crabs in considerable numbers on the bottoms 
in the southern part of the Bay during the winter, and an abundance of sponge-bearing 
crabs in the southern waters the following June. Every evidence points to the fact 
that the mature female crabs which mated in Maryland waters migrate to the southern 
part of the Bay and spawn there the following summer. 
Records were kept of various catches made by the dredge boats at intervals during 
the winter of 1916-17. Fourteen lots dredged in the lower part of the Bay gave an 
average percentage of 85 females to 15 males. Four lots dredged from points north of 
the city of Cape Charles, Va., gave 55 females to 45 males. It is safe to say that at 
least 80 per cent of the adult crabs found on the bottoms in the lower part of the Bay 
during the winter are females. 
In brief, the migrations of a majority of the crabs of Chesapeake Bay are as follows: 
They hatch in the southern part, move northward as they develop and molt, lie on the 
bottoms where winter overtakes them, resume their northerly course in the spring, 
continue molting, reach maturity in the waters of upper Virginia and central Mary- 
land, and mate there. The females return south in the autumn, lie on the bottoms 
of the southern part of the Bay, and spawn the following summer, the males remaining 
mostly in more northerly waters. A certain number do not migrate, but spend their 
entire life in the lower part of the Bay. Some small crabs may be found there during 
the entire summer. The great majority, however, of the young migrate as described 
above. 
GENERAL HABITS. 
Hay ® presents an excellent description of the general habits of the blue crab. 
Certain portions will be quoted as affording the most convenient method of presenting 
these interesting features of the natural history of the blue crab. 
Hither 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 
apparently 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 
@ Hay, op. cit., pp. 401-403. 
