APPENDIX H: GARSTANG 



4 — 



Table I, showing the number of plaice marked and liberated to the end of 1903, and recovered 



to the end of June 1904 



The object of these experiments was three-fold, viz., first, to throw light upon the natural 

 migrations of the plaice in different regions and at diiferent seasons of the year, secondly, to 

 contribute to our Icnowledge of the rate of growth of tliis species, and, thirdly, to yield information 

 concerning the intensity of fishing under modern conditions. 



The results attained under the first of these heads are clear and convincing, and will be 

 dealt with in further detail below. Differences in the method of marking adopted in the different 

 countries do not appreciably affect the conclusions which are to be drawn upon this point. 

 But quantitative problems like the rate of growth and the intensity of fishing depend for their 

 solution upon the suitability of the methods employed. A glance at the preceding table shows 

 that considerable differences with regard to the percentage of fish recovered have been mani- 

 fested in the course of the experiments. It is therefore desirable at the outset to make a brief 

 statement as to the methods pursued in different countries. In Sweden, Denmark, Holland and 

 England Petersen's method of marking flat-fish has been adopted. This consists in passing a 

 small piece of silver wire through the dorsal edge of the body, about half-way down, below 

 the base of the dorsal fin, and in attaching a couple of small discs to the wire, one on the 

 upper or eyed side, and one on the lower or blind side. „The lower disc is invariably made of 

 bone. In the Danish experiments the upper disc also consists of a bone button bearing a 

 distinctive number stamped upon it. As, however, the number is liable under these circumstances 

 to be obliterated after a few months by wear and decay of the bone, Dr. Petersen has added 

 an additional brass disc bearing the same number and superimposed upon the upper bone button. 

 Numbered bone buttons were also used in the earlier Swedish, Dutch and English experiments, 

 but were soon replaced entirely by a special brass disc of concave form, which has proved to 

 be a very satisfactory substitute. Little injury is caused to the fish by the use of labels upon 

 Petersen's model, and the rate of growth does not appear to be much retarded by the employ- 

 ment of this method, although excessive looseness or excessive tightness of the wire qccasionally 

 leads to abrasions of the skin. There is only one recorded instance of a marked plaice having 

 already died before, it was recaptured by a fisherman, viz., Da 220, which was caught near 

 the Vyl Lightship four days after it was liberated in April, 1903. This instance, however, 

 is of importance in showing that the percentage of marked fish recovered by the fishermen can 

 only claim to be a minimum measure of the intensity of fishing, especially as regards the 



' This is the percentage of fish recovered within twelve months after date of liberation, and is not 

 expected to agree with the percentage calculated from the figures given (see Table III). 



