320 THE SEAS 



to the fishing industry, the herring, indeed, being one of the 

 most important of all fish from the waters on the north- 

 eastern part of the Atlantic. The plaice make up a large part 

 of the catches of the trawlers in the North Sea while the 

 pursuit of the herring constitutes that great drift-net fishery 

 which takes place around our coasts chiefly in the late 

 autumn and winter. This distinction points at once to a 

 fundamental difference in the behaviour of these two 

 fish. The plaice which are captured by the trawls that 

 scour the sea floor are bottom-living or demersal fish, 

 while the herring, as their mode of capture suggests, live, 

 for considerable periods at any rate, in the water layers 

 above the bottom and are pelagic. 



In studying the life-history of a fish it is best to start 

 right from the beginning and watch the growth and move- 

 ments of the individual from the time it is first brought 

 forth by the parent fish as an egg. 



Let us, therefore, put ourselves in the place of the early 

 naturalists, the founders of fishery research, and imagine 

 that we must set out to find the eggs of the herring and the 

 plaice. We should immediately say, " How can we find 

 them if we do not know what they are like to look at ? " 

 This brings us to the very first step in the study of the life 

 of a fish. The eggs when discovered must be accurately 

 described and figured so that those who come after us 

 may know at once what to look for. 



Towards the end of the nineteenth century a controversy 

 arose as to whether the advent of the steam trawler might 

 not have a harmful effect on the sea fisheries by destroying 

 in large quantities the eggs of the fish as the heavy net was 

 dragged over the bottom. In the year 1864 the great 

 Norwegian naturalist, Prof. G. O. Sars, discovered large 

 numbers of eggs drifting in the surface water layers well 

 above the bottom, and was able to show that these were 



