404 A HISTORY OF FISHES 



have been taken, the dangers of over-fishing are not now 

 beheved to be so very serious. The fact remains, however, 

 that twenty-five per cent, of the catchable Plaice, that is to 

 say, of fish big enough to be retained by the meshes of the 

 nets, are taken out of the sea every year, and the situation 

 requires to be carefully watched if the stocks of this valuable 

 species are to be preserved for future generations. 



Apart from the laws designed to conserve the existing 

 stocks of fish — the prohibiting of the capture of young fish, 

 closing of certain grounds, establishment of close seasons, and 

 so on — the only possible means of sustaining or increasing the 

 stocks of demersal fish in a region such as the North Sea lies in 

 the artificial rearing of young fish or in the transplantation of 

 young or mature fishes from other localities. The hatching 

 of the eggs of Plaice and other Flat-fishes in special tanks, 

 the rearing of the larvae through the critical period of their 

 lives, and their subsequent liberation in the sea, has been 

 carried out in hatcheries established at the Bay of Nigg in 

 Scotland, Port Erin in the Isle of Man, and Piel on the Lan- 

 cashire coast. Large numbers of fry have been released, but 

 the chances of increasing to any appreciable extent the existing 

 stocks of fish by such artificial methods are at present very 

 remote. After all, what are the few millions of fry liberated 

 every year to the many miUions already in the sea? Trans- 

 plantation, as a method of replenishing depleted stocks, has 

 been tried in the North Sea with some success, but the obstacles 

 to be overcome before it would be practicable to carry this out 

 on a scale sufficiently large to have any definite eflfect on the 

 resources of the North Sea are at present rather great. Small 

 Plaice were caught off the coast of Holland, marked with discs, 

 and half of them liberated on the spot, the remainder being taken 

 alive in special tanks and released on the famous Plaice ground 

 on the Dogger Bank. When the marked fish were subsequently 

 recaptured, it was found that those on the Dogger Bank, a 

 locality known to be particularly rich in a certain kind of 

 shell-fish to which the Plaice is partial, had grown very much 

 faster than those on the Dutch coast, where the food supply is 

 less abundant. 



It was the pressing need for a scientific investigation of the 

 alleged decline in the numbers of fish, due to over-fishing, 

 coupled with the increased interest taken in the science of 

 oceanography, which had received a marked stimulus from 

 the Challenger expedition in 1872 to 1876, that led to the 



