SEA-FISHERIES LABORATORY 245 



REPORT ON PLAICE MEASUREMENTS MADE 

 DURING THE YEAR 1912. 



By Jas. Johnstone, B.Sc. 



This Report deals with measurements of plaice made 

 during the year 1912, and forms a continuation of the 

 similar measurements made during the last four years. 

 The primary object of these investigations was to provide 

 data for a rational discussion of the effects likely to follow 

 from the adoption of the 6-inch trawl mesh in place of the 

 7-inch mesh — a question of considerable local importance 

 during the last few years. The data already accumulated 

 have proved sufficient for this purpose, but the measure- 

 ments have been continued for several reasons : (1) it is 

 hoped that they may be useful in future investigations 

 by providing fairly accurate data as to the modal lengths 

 of plaice on the fishing grounds at various seasons ; such 

 information, if it had existed for (say) the year 1870, 

 would now be of the greatest interest. (2) A study of 

 the variation in length on the various grounds is of 

 assistance in the interpretation of the results of the 

 marked-fish experiments, and, in general, the problem of 

 plaice migrations. (3) It is hoped that they will provide 

 data for the determination of the lengths of plaice at 

 different ages, and of different sexes, and for that of the 

 age and length at which these fish become sexually 

 mature for the first time. (4) The estimates of the 

 " condition " of the fish, that is, the values of the co- 

 efficient k may be of service in a study of the relationship 

 between the physical conditions of the sea and the rate of 

 metabolism of the fish. 



The arrangement of the data is much the same as in 

 previous years. The length-frequencies are first given. 



