120 



Part III. — Eighteenth Annual Report 



shore. Of these crabs, 131, that is 8 per cent., have been recaptured. 

 There are certain circumstances which tend to lower the number of the 

 crabs which may be recaptured, viz. (1) the chance of the label being 

 torn off; (2) the risk of death following the treatment to which the 

 crab is exposed while being brought ashore, labelled, and returned to 

 the water. The percentage of recovered crabs is very much lowered by 

 the very few crabs recaptured during the first part of the experiment. 

 Of 539 crabs labelled from October 1897 to April 1898, only 12 were 

 recaptured. Of 1028 labelled since November 1898, 119 have been 

 recovered, viz. 11*5 per cent. The crabs were marked by attaching, by 

 means of a silver wire, a nickel label, about | to f inch square, to a small 

 hole bored in the edge of the shell, usually at the seventh septum on 

 the left side. At first small brass labels were used ; some of these were 

 attached by fine brass snare wire to the great claw, others were attached 

 in the same manner as the nickel labels. Two only were recovered 

 with the label tied to the claw. Nickel labels were alone used for the 

 crabs labelled from 1 to 1173. The number of crabs set free at one 

 time, the date, and the place are given in Tables X. and XL On the 

 right side of the Table the particulars regarding the recaptured speci- 

 mens, their condition when set free, and when and where recovered, 

 the length of the interval of freedom, etc., and in a number of cases the 

 sex and size of the crab, are detailed. Table X. contains the crabs put 

 away at the mouth of the harbour ; Table XI., those returned to the 

 sea at various distances from shore. 



The majority of the crabs used for labelling were soft gauge crabs, in 

 number 999; 568 hard crabs, viz. 532 small crabs measuring 3| to 4J, 

 and 36 gauge crabs, were also marked. The small hard crabs were 

 used for labelling from January to July ; the large hard crabs in J une 

 and July ; the soft crabs from July to December. Of nine batches, 

 consisting of 333 marked specimens, no individual was recovered. 

 The date and other particulars of these lots are given in the following 



Date. 



Number 



of 

 Speci- 

 mens. 



Descrip- 

 tion. 



Mode of Attachment 

 of Label. 



Place where set free. 



Oct. 29, 1897, 



52 



Soft, 



Attached to great claw, 



Mouth of harbour. 



Nov. 1, ,, 



51 





55 35 55 



33 »3 



Dec. 2, 



19 



> > 



5 J 5 5 3 5 



33 33 



24 



5 5 3 5 



35 





to edge of shell, 



35 >> 



J» >> 33 



19 



*u. Hard : ,, ,, ,, 



55 >> 



Feb. 26, 1898, 



22 



> > 



,5 5 3 3 3 



4 miles N. of Dunbar. 



Mar. 1, 



35 



" 



3 3 33 35 



5 3 5 > 



May 13, 1899, 



50 



>» 



33 35 55 



3 miles E. by N. of 

 Dunbar. 



>, 25, „ 



50 



) 5 



5 3 5 5 3 3 



Mouth of harbour. 



* Under gauge size. 



Very few small hard crabs were recovered, viz. 16 only out of a total 

 of 532. This was in some measure no doubt due to the fact that the 



