HADDOCK FISHERY 97 



SESSIONAL PAPER No. 38a 



(C) STUDY OF SCALES TO DETERMINE AGE OV HADDOCK. 



Scales were obtained from the fish of the first eleven catches examined. Those 

 of seventy-four have been carefully studied. The scales were taken from the shoulder, 

 above the lateral line just behind the head. They were washed in water, brushed 

 with a small stiff paint brush to remove the mucus and epidermis, and mounted dry 

 between two slides. 



The morphology of the gadoid scale has been carefully woj-ked out by Dr. Damas 

 in connection with the North sea investigations. He examined the scales of the cod 

 which very closely resemble those of the haddock. The haddock scale is ovoid and 

 when magnified appears to be mad'C up of numerous concentric rings. The distance of 

 these rings from one another varies in a definite periodic manner. The first rings about 

 the nucleus are relatively wide apart, outside these the rings come close together 

 forming a so-called "winter ring," outside of which they are suddenly farther apart 

 again. By studying cod scales at different seasons of the year Dr. Damas concluded 

 that the region where the rings were well separated represented rapid growth under 

 the favourable conditions of summer, and the narrow compressed rings were formed 

 during the winter months. Each band of summer and winter growth together repre- 

 sent one year of the fish's life and the age of the fish can therefore be estimated by 

 counting the number of winter rings on its scales. Fig. 2 shows the margins of 

 successive winter rings on a scale of a four-year-old fish. 



In a length frequency curve for the separate ages dTawn after determining 

 the age of each fish from a study of its scales, an obvious fact to be plainly deduced 

 from this curve is that we have not sufficient data from which to draw satisfactory 

 conclusions as to the most abundant size for any one age. It appears that the year 

 classes overlap one another to a considerable extent, and that the overlapping becomes 

 greater after the fourth year. This shows that growth is slower and more irregular 

 after the fourth year, which is probably the age at which the haddock mature. 



'We can deduce the following year classes: — 



Comparing the averages of these classes with the averages deduced from the first 

 length frequency curve (Fig. 3B) we find a striking correspondence in the first four 

 classes. 



38a— 7 



R— 16 



