of the Fishery Board for Scotland. 



77 



II.— CONTRIBUTIONS TO THE LIFE -HISTORY OF THE 

 EDIBLE CRAB (Cancer pagurus, Linn.). 



By H. Chas. Williamson, M.A., B.Sc. (Plates I.-IV.). 



CONTENTS. 



PAGE. 



Introduction, ........ 77 



Size of Crab at Maturity : — 



The Mature Female Crab, ..... 79 



Fertilisation, ........ 82 



Annual Spawning, ....... 85 



Times of Spawning and Hatching, .... 88 



Number of Eggs of Berried Crab, .... 89 



The Mature Male Crab, ...... 97 



External Sexual Characters, ...... 98 



Proportional Numbers of the Sexes, ..... 99 



Exuviation, Casting, ....... 104 



The Occurrence of Soft Crabs : Hardening of Shell, . . 105 



Frequency of Casting : Increase in size, .... 109 



Regeneration of Lost Limbs : the Repair of Injuries, . . . Ill 



Rate of Growth and Distribution, . . . . . .113 



The Migrations of Crabs : Labelling Experiment, . . . 119 



The Regulation of the Crab Fishery, . . . . .134 



The edible crab (Cancer pagurus, Linn.) is to be found on all the 

 coasts of Great Britain and Ireland. It gives rise to important 

 fisheries, the chief of which are in the English Channel, and on the east 

 coasts of England and Scotland. Owing to the fact that the crab is 

 found close to the shore, the fishery may be carried on with small boats. 

 In 1877, as a result of the report of the Crab and Lobster Commission 

 of 1876-7 the Fisheries (Oyster, Crab, and Lobster) Act was passed. 

 With a view to develop the fishery, and to check a tendency to deteriora- 

 tion which was evident in certain districts, the measure prohibited the 

 sale of (1) any crab less than 4| inches across the broadest part of the 

 back, (2) any soft crab, (3) any berried crab. The first and second 

 classes of crabs are practically unsaleable ; berried crabs are seldom 

 captured. The law, however, made an exception in the use of crabs for 

 bait ; so that while small, soft, and berried crabs could not be sold, they 

 might be broken up for bait. The result was that the law, so far as 

 protection was aimed at, was to a considerable extent inoperative. In 

 certain places crab fishing is carried on more or less for the greater 

 part of the year ; in some districts, however, during autumn, when a 

 considerable proportion of the catch consists of unsaleable crabs, viz., 

 soft, and when the price falls in consequence of the inferior quality of 

 some of the saleable crabs, viz. those which have just become hard, Yhe 

 fishermen discontinue this for some other mode of fishing. In Dunbar, 

 a port which may be said to have devoted itself specially to crab fishing, 

 the fishery is pursued during the whole year, with, however, intervals, 

 during which the majority of the men take up the summer and winter 

 herring fishing. Within the past few years the crab fisheries of 

 England have attracted a large amount of attention from the District 

 Committees, which were created by the Sea Fisheries Regulation Acts, 

 1888-1894. The shortcomings of the Act of 1877 have been recognised, 



