SEA-FISHERIES LABORATORY. 367 



state that contrary opinions have been expressed. It is at 

 first sight a paradox that year by year the total catch of 

 fishes in British waters should increase, while the fishing 

 grounds may be really deteriorating. Along with this 

 increase in total quantity of fish caught, however, has 

 gone on a marked increase in the catching powers of the 

 fishing fleets and an extension of the area fished over. 

 The introduction of steam into fishing vessels about 1850, 

 and the use of ice for preserving the catches, made possible 

 the use of larger and more efficient apparatus (the otter 

 trawl latterly), and enabled the vessels to make longer 

 voyages. With this change the small sailing boats began 

 to decrease in numbers, and fishing instead of being car- 

 ried on by vessels independently owned by masters or 

 crews, became a great capitalised industry. 



Therefore although the annual catch has gradually 

 increased, the average catch per vessel is now beginning 

 to decrease, and the density of the fish population in the 

 seas round the British Isles is less than it formerly was. 

 The catches of 4 Grimsby sailing trawlers for every year 

 since 1875 have been published by Grarstang,* and all of 

 these shew a marked decrease w T ith hardly any fluctuations. 



In Danish seas the same decline has been noticed. 

 Petersen! has shewn that there has been a steady decrease 

 in the size of the Plaice landed for many years, and it is 

 obvious that the reduction in size of the fish landed is 

 indicative of the reduction in number of those present on 

 the fishing ground. i 



* See Garstang Mar. Biol. Assoc. Journ. for these figures and the 

 elaboration of the above argument. 



f 4th Rep. Danish Biological Station, 1893. 



X From the relation between the average size at first maturity and the 

 average size of all mature plaice captured, the change in the fish population 

 of an area may be deduced. See Kyle- 18th An. Rep. Scottish Fish. Bd., 

 1900, p. 200, 



