278 THE SEAS 



catching these in the trawl also. When fishing for herring 

 however the mesh of the net is somewhat reduced and the 

 trawl is towed at nearly the full speed of the vessel, as 

 opposed to the two and a half to four knots under usual 

 trawling conditions. 



Drift Fishing 



Most of our food fish live on or near the bottom and can 

 be scooped up by the trawl, but two or three species, such 

 as the herring and the mackerel, live a great part of their 

 lives swimming in huge shoals in the water layers above the 

 bottom. In the daytime they are usually swimming 

 rather deep in the water, but at dusk and during the night 

 they come up very close to the surface itself. It is then 

 that they can be most easily caught in the specially 

 designed nets known as " drift nets." This habit of coming 

 towards the surface at night is not peculiar to herring and 

 mackerel. Those drifting animals that form the plankton 

 show these habits and such vertical migrations are also 

 common to many other fish. The hake is an excellent 

 example ; so regularly does this fish leave the bottom at 

 night that the fishermen never trawl for them except in 

 the daytime, when they are on the bottom. 



The drift nets by which the herrings are caught act on 

 a principle very different from that of the trawl. There is 

 no bag into which the fish are swept. A drift net is literally 

 a wall of netting hanging vertically in the water, and in 

 this case it is the mesh of the net that catches the fish 

 (Plate 98). This mesh is made so that the herring can 

 exactly push his head through, but not his body. When 

 once the head has been pushed in beyond the gill-covers 

 it is impossible to get it out again, because, the gill-covers 

 being slightly raised, the twine of which the mesh is made 

 slips under them. The herrings, swimming in vast shoals. 



