SEA-FISHERIES LABORATORY. 107 



considerable space is saved by the grouping, and no 

 serious error is involved. 



All the Tables from p. 153 to p. 171 relate only to 

 these measurements of length made immediately after 

 capture of the fish. The actual frequencies are given 

 under the headings "Nos.," and then these frequencies 

 have been converted into percentages of the whole catch 

 accurate to the first decimal place. Representation of 

 the frequencies as percentages of the total catch assists in 

 making comparisons, and enables us to draw graphs to 

 the same scales of coordinates for all the catches. 



The Tables "Age-Groups, 1909," which occur on 

 pages 172 to 178, represent the ages of those plaice 

 examined according to the conventional grouping : Age- 

 Group includes fish to 1 year old, I fish 1 to 2 years 

 old, and so on. The first group is seldom represented 

 in catches made with a trawl net of 6-inch mesh, and 

 has not been considered. Age-groups higher than III 

 are also very sparingly represented in most of the 

 localities, with the exceptions of the offshore grounds 

 near Bahama Bank, and in Luce Bay and the Clyde 

 area. " Lumping " can only be practised here to a very 

 limited degree. It is permissible to combine the measure- 

 ments relating to the same month, though even this 

 involves error during the period of most rapid growth. 

 The measurements made during the months January to 

 March and September to December may, however, be 

 combined, since growth is minimal during these seasons. 

 Obviously one cannot combine the results from different 

 grounds without risk of error. 



The Table " Modal Lengths of Plaice captured by a 

 6 -inch Trawl Mesh, 1909," p. 179, summarises the 

 measurements so far as the modal, or characteristic 

 lengths, are concerned. These lengths are given for each 



