RAPPORTS. XIII C2: THOMPSON 



12 — 



centimetres, after which it begins to fall gradually; in other words, this would seem to 

 be the point at which the otter trawl began to retain all the fish that came within its 

 meshes, while below this size a greater and greater percentage of the fish escaped and 

 slipped away. This fairly obvious deduction is corroborated by an inspection of the 

 Table of our small mesh catches (Table II), where we see that the numbers of Cod found 

 in the small mesh net became infinitesimal after just about the same size of 27 centi- 

 metres. 



, "f^Looking now at the Firth of Forth curve, we see that while it approximates to a 

 straight line, it does not do so so closely as does Mr. Edser's plaice curve for the South- 

 ern portion of the North Sea. We seem to have a pretty steady rate of fall up to a 



10 20 ^ 30 40 50 60 70 80 90 



Fig. II. Sizes (and approximate ages) of Cod from the Aberdeen coast: 

 S. S. "Goldseeker", 1903 — 1909; January— March. 



size a little over 50 centimetres, while after that the fall is steady, but more rapid. I 

 think it highly probable that this means that, above that size, that is to say after the 

 corresponding age of between two and three years, the numbers of Cod within the Firth of 

 Forth tend to diminish by migration seawards over and above the diminution to which 

 they are subject by capture and by natural mortality. In the Moray Firth curve no very 

 striking points of novelty appear, for other features are overshadowed by the one conspi- 

 cuous phenomenon of the great scarcity of fish from 50 to 80 centimetres, and of the 

 return in abundance ot the fish of greater size. 



We have in the next place a series of curves (figs. 11 — 14) from the East Coast of 

 Scotland, that is to say from a number of stations between the Firth of Forth and the 

 Moray Firth, chiefly off the Aberdeenshire Coast and all at no great distance from the 

 coast. Again it is impossible to deal with these here in great detail, but it is interesting 

 to note that, while we have nothing on so great a scale as the great immigration of 



