37 



THE PLAICE FISHERIES OF THE IRISH SEA 



BY 



JAS. JOHNSTONE, D.Sc; W. BIRTWISTLE 

 AND W. C. SMITH 



CONTENTS 



PAGE 



PART I: The Pke-War Period, 1908-1913 39 



Introduction ... ... ... ... ... ... ... ... 39 



The area investigated, p. 40 ; Nature and regulation of the 

 grounds, 42 ; Distribution of the various species of fish, p. 45 ; 

 Tables I and II, species of fish found, p. 46 ; Seasonal fisheries, 

 p. 49 ; Migratory fishes, p. 50 ; Long period fluctuations in 

 the fisheries, p. 52. 



Methods of investigation ... ... ... ... ... ... 53 



Treatment of the data ... ... ... ... ... ... ... 55 



Statistical methods, p. 56 ; Pearson curves, p. 58 ; Summational 

 curves, p. 60 ; Use of the same, p. 65 ; Measures of dispersion, 

 p. 67. 



Lengths of the plaice caught ... ... ... ... ... ... 71 



Tables III to XIII, Length frequencies on the grounds during 

 1908-1913, p. 73 . Prevalent lengths, 85. 



PART II : The Life-History of the Plaice 

 The spawning grounds ... 

 The hatching and transformation stages 

 The first shore stages ... 

 Food of the larvae and transformed plaice 

 Growth of the plaice during the first year 

 The nursery grounds and their conditions 



88 

 93 

 94 

 95 

 96 

 99 



The rate of growth of the plaice ... ... ... ... ... 102 



Tables XIV and XV, length frequencies for age-groups 0-IV, 



p. 104 ; Ratio of males to females, p. 107 ; Sizes at sexual 

 maturity, p. 108. 



