SEA-FISHERIES LABORATORY. 113 



the modal length +%, and negative values the modal 

 length - x ; and positive values of y represent the modal 

 frequency + y, while negative values are the modal 

 frequency - y. I have drawn and discussed several such 

 diagrams in a later section of the report, and it will be 

 seen at once that these afford a picture of the changes 

 taking place on the fishing grounds. Parts of each curve 

 are, as it were, eaten away, showing how the fish popula- 

 tion has changed as the result of the operation of several 

 factors. 



Several diagrams are given in section 5 showing 

 the relation of length and weight in plaice. That on 

 p. 141 represents the average weight, in relation to mean 

 length, of plaice caught in Barrow Channel, Rock 

 Channel and in Beaumaris Bay. Such curves can be 

 drawn by making use of the length-weight coefficients 

 tabulated on p. 179: they are the graphs of the function 



kl 3 

 g — -jt=, when the suitable values of k have been 



substituted. The theoretical curve differs hardly at all 

 from the smoothed curve of actual values represented in 

 fig. 79. 



The construction of the graphs representing the 

 length-frequencies in Age-Groups I, II and III will be 

 discussed in a later section. 



The probable errors of the modal lengths have not 

 been calculated. So far a comparison of the results of 

 the measurements with similar data for other years is not 

 possible. In any such comparison, due allowance will 

 have to be made for the probable errors. 



3. MODAL SIZES OF PLAICE ON THE FISHING 

 GROUNDS. 



The determination of the modal sizes of the plaice 

 inhabiting the various fishing grounds has been the prin- 



