WHAT IS OVEK-FISHLN-G i 589 



fourteen to ten inches (Diagram, Illb), and statistics show a decreasing 

 value year by year in the North Sea taken as a whole, the North Sea 

 being a biologically well-defined area for the "P." * 



This being the fact, what can be the reason or the reasons for the 

 declining statistics and for the reduced average size of the "P" in this 

 area ? The catching power has been much enlarged, the prices have 

 risen, and the physical conditions have not undergone any unfavourable 

 change ; so the decrease in value of the total yearly catch must be 

 ascribed to organic factors, i.e. to man or to other organisms. 



Has the bottom been injured by trawling in such a way that the food 

 of the " P " has been destroyed ? 



This view was held in former times, but has never been proved 

 or set forth in such a way as to make it probable. If the "P's" food 

 was destroyed, we might suppose that the "P" in consequence would 

 look very lean, or not be able to grow, as the case is in the Baltic. 

 Marking experiments, nevertheless, prove that the "P" grows fast 

 when not too abundant in a narrow space. Overcrowding may perhaps 

 be found on certain grounds, this being actually the case in the Western 

 Lim Fjord ; but in other parts of the Lim Fjord the " P " grows very 

 fast where it is scarce. Experiments of mine specially directed to this 

 point have shown that the small invertebrates are still as numerous per 

 square foot in the western part as in many other places in the Lim 

 Fjord. Speaking generally, we cannot consider that food is wanting in 

 the North Sea, at any rate not to a greater extent than formerly ; but 

 in the present state of our knowledge is it possible to suppose that 

 other invertebrates, e.g. the star-fish Asterias ruhcn-s, eat the small 

 bivalves which are the best "P" food, and that Asterias is more 

 numerous at the present time because the large " P " indi\dduals have 

 disappeared from many fishing grounds ? Investigations on the actual 

 rate of growth of the " P " in such localities may solve this problem — 

 at any rate, they may prove how fast that "P" is growing, which is the 



* I am extremely familiar with this kind of fishing upon the II Group, since the plaice 

 lives in the Tnm Fjord, but does not propagate there, perhaps because all plaice are fished 

 out there every autumn when they have grown some few inches during the spring and the 

 summer. The young ones immigrate in numbers every year from the North Sea. In the 

 Lim Fjord we have no true stock at all. What must, then, be thought of the Lim Fjord 

 fishery ? Is it "destruction of immature fish," since all are fished out before they reach 

 maturity, and almost entirely fished out every year ? The Lim Fjord, however, is not a 

 biologically self-contained area for the plaice, and this question accordingly forms only a 

 part of the whole over-fishing problem. The Qord gets its young plaice from the North 

 Sea every spring, and we in Denmark have only the two things to do : ( 1 ) To help into the 

 Qord as many as there is room for, and this is limited, and (2) to leave them in peace 

 during the summer to grow up to a saleable size, like carps in a carp pond. As we get our 

 young plaice every spring for nothing, or almost for nothing, and as they reach a good size 

 for sale during the six to eight months, they ought to be fished out every autumn and 

 winter. 



