155 



about 90 per cent, of all those that are less than 8 cms. in 

 length belong to Age-group 0. This arbitrary limit has 

 therefore been taken in Table 20, and the proportions of 

 plaice of less than 8 cms. long have been calculated and regarded 

 as giving us a good idea of the relative abundance of young 

 fish resulting from the spawning of the months March and April 

 immediately before. In this way Fig. 20 has been made. 



% 

 80 



4-0 



poa ipo^ ^i^io 



'J>/3 'I9'H- '191s- 



igib 



1917 ' 191& 



91^ • l<pS.O' 1^2.1 



Fig. 20. Graph showing the productivity of the spawning seasons 

 during the years 1908-19. The heights of the rectangles are proportional 

 to the numbers of plaice larvae reaching the nursery grounds. 



We see that 1908-11 and 1913 were good years in that 

 large numbers of young plaice came on to the nursery grounds. 

 The years 1912, 1916, and 1918 were bad ones — years in which 

 there was an unusually small production of young plaice. 



It would be miprofitable to pursue this matter further, 

 for hardly any data exist, just yet, which would enable us to 

 look for the reasons why some years are better than others. 



Tables 21 to 27 now follow : these give the results of 

 measurements of plaice made in the Irish Sea during the 

 year 1920, and they are intended to provide the data for more 

 minute comparisons with the pre-war period than we have 

 now the opportunity to undertake. 



