476 REPOllT ON TRAWLING AND OTIIEK INVESTIGATIONS 



experiments. The difference, however, is apparently attributable, not 

 to any permanent change in the distribution and abundance of the 

 fish caused by the closure of the bays, but principally to a temporary 

 scarcity during 1901-2 of medium-sized plaice from 8 to 11 inches 

 in length (three to four years old), caused by an unfavourable 

 spawning season in 1898. 



2. THE :\IIGKATIONS OF THE PLAICE. 



In order to provide some definite information as to the movements of 

 plaice to and from the bays, a considerable number of living fish were 

 marked with numbered labels and set free in the autumn of 1901 and 

 the early summer of 1902. After some preliminary experiments with 

 other devices. Dr. Petersen's method was adopted. This consists in 

 passing a small piece of silver wire through the dorsal edge of the body, 

 about half-way down, between two of the interspinous bones below the 

 base of the dorsal fin, and in attaching a couple of special bone buttons 

 to the wire, one on the upper (or eyed) side, and one on the lower (or 

 blind) side. One, and in some cases each, of the buttons bore a dis- 

 tinctive number stamped upon it. The numbered bone button on the 

 upper side was advantageously replaced in some of the experiments by 

 a thin oval disc of brass, also numbered. By this modification of 

 Petersen's method the obliteration of the number by wear and decay 

 of the bone was obviated, and the fishes appear to have suffered little, 

 if any, inconvenience. The only observed injuries caused by the label- 

 ling were due to an accidental slackness of the wire in two or three 

 cases, thus causing the hinder margin of the lower button to catch and 

 cut into the skin. In the great majority of cases, however, the fish 

 were recovered in good condition. 



Neglecting the preliminary trials, the marking experiments fall into 

 two groups: (1) fish marked and liberated in the bays in the autumn 

 of 1901 ; and (2) fish marked and liberated outside the bays in the 

 early summer of 1902. The details of liberation and recovery are 

 given in Table XXV. 



I. Start Bay. 



Four batches of marked plaice were liberated in Start Bay between 

 the 2nd October and the 9th November, 1901. During October 159 

 were marked, and during November 108, making a total of 267. Of 

 these 62 fish had been recovered to the end of July, 1903, i.e. 23^ 

 per cent. Of these 34, i.e. 13 per cent., were recovered in the first 

 six months, and 23, i.e. 8^ per cent., in the second six months, making 

 a total of 2H per cent, recovered within one year of liberation. The 

 size of the fishes marked varied from 17*5 cm. to 46 cm., i.e. from 



