SEA-FISHERIES LABORATORY. 



183 



This, it will be seen, is a " small-fish " ground. 

 About 50 % of all tbe plaice caught in a trawl-net of 

 6-inch mesh are between about 17'5 and 21'5 cms. in 

 length. 



The population on this ground is not a stationary 

 one, a conclusion which may be deduced from the length 

 statistics no less clearly than from the marking experi- 

 ments. The modal length shows a general rise throughout 

 the period investigated, but this increase is not a regular 



Length-Frequencies of Age-Group II $ 2 at Nelson Buoy, 



1909-1913. 





May. 



June. 



July. 



August. 



14-5 



2 



1 







15-5 



6 



4 



4 



1 



16-5 



17 



11 



14 



4 



17-5 



23 



37 



29 



15 



18-5 



13 



57 



73 



37 



19-5 



19 



87 



95 



47 



20-5 



10 



74 



53 



42 



21-5 



14 



69 



43 



37 



22-5 



15 



28 



31 



19 



23-5 



6 



16 



21 



16 



24-5 



4 



11 



7 



6 



25-5 



5 



5 



10 



5 



26-5 



4 



2 



4 



2 



27-5 



— 



2 



1 



2 



28-5 



— 



3 



1 



— 



29-5 



— 



1 



— 



— 



30-5 



— 



1 



— 



— 



31-5 



— 



1 



— 



— 



Mean 



19-79 



20-43 



20-2 



20-97 







Error of 











Mean 



± 0-16 



± 0-19 



± 0-07 



± 0-09 



one. If we consider only the plaice of Age-Group II, 

 instead of all the fish caught, so as to obtain a homogeneous 

 frequency distribution, we still find that these fish do not 

 grow regularly, that is, although the mean length of the 

 plaice sampled rises from 19-79 in May to 20-97 in 



