SEA-FISHERIES LABORATORY. 469 



Distribution and Migration. 



According to Williamson,* the crabs after the larval 

 stages may be placed in four different groups according 

 to their distribution. 



Group I includes the young stages up to J-inch in 

 breadth. These are probably restricted to the shallow 

 shore waters. 



Group II includes the crabs found on the beach 

 between tide-marks. From ^-inch to 2\ inches in breadth. 



Group III includes the crabs living in the littoral 

 waters beyond low-water mark. From 2\ to 4 inches. 



Group IV includes all the crabs above 4 inches in 

 breadth. These crabs are mostly mature, and migrate 

 from the inshore waters in the summer to the deeper 

 offshore waters in the winter. 



With regard to Group I, my own observations 

 confirm those of Williamson. In the spring and summer, 

 when small specimens of Cancer must be very abundant, 

 they are very rarely found between tide-marks. On the 

 other hand, they are frequently taken in the. dredge close 

 to the shore. 



The migration of the mature crabs has been long 

 known to fishermen, and our knowledge with regard to 

 this subject is now fairly complete, thanks to the work of 

 Williamson, Meek and others. Only the crabs of 

 Group IY are concerned in the migration, which may be 

 divided into an offshore migration in the autumn and an 

 inshore migration in the spring. Both hard and soft 

 crabs begin to move outward into the deeper water in 

 September (see Text fig. 13). The extreme depth to 

 which they travel must necessarily vary with the locality, 

 but it is generally between twenty and thirty fathoms. 



* Williamson. Eighteenth Annual Report. 



