282 FISHES AND MAN xi 



expect the larger and nearer aggregations, but there is still much to 

 be done in tracing the migration and behaviour of pelagic fishes. 

 It is not impossible that other pelagic fisheries could be developed 

 that would be at least as advantageous as the herring fishery. Besides 

 those eaten fresh, others are preserved as kippers by salting and smok- 

 ing, or are heavily salted and smoked to make 'red herrings' for which 

 there has been a large export market. 



Lining is a method that can be used for either pelagic or demersal 

 fish. For instance, the cod fishery of Newfoundland uses lines with 

 several thousand baited hooks. Inshore fishing may be accomplished 

 by beach seining, a process of enclosure of the fish from the shore. 

 There are also various forms of trap into which the fish swim and 

 cannot escape. Danish seining, or purse seining, completely surrounding 

 the fish and sometimes then also drawing the bottom of the net 

 together, is another effective method. 



The greatest quantities of fish are caught, however, by the various 

 forms of trawling. These depend essentially on dragging a bag along 

 the bottom of the sea, and the different types adopt various means of 

 keeping the bag open. The earlier way of doing this was by means of 

 a rigid bar and these beam trawls sometimes used poles over 50 ft 

 long. More recently otter-trawling has replaced the beam trawl, the 

 otter boards being flat wooden structures attached at each end, so as 

 to sheer away when they are dragged through the water, thus opening 

 the net. Various devices are used to stir up the fish from the bottom; 

 in particular the otter boards are now usually separated from the net 

 by long wires and a 'tickler' chain is attached in front of the mouth. 



With such methods very large amounts of fish can be taken from 

 the sea bottom. In i860 sailing-ships landed 500 tons of fish at 

 Grimsby; by 190 1, 176,000 tons were landed from the steam traw lers 

 50,000 tons of plaice alone are taken annually from the North Sea. 

 There is evidence that the taking of such amounts of fish from rela- 

 tively confined waters has a large influence on the population. For 

 instance, it is estimated that 45 per cent of the stock of plaice is 

 caught each year in the North Sea. Under these conditions man pro- 

 vides the main source of mortality for the fishes. It is less clear 

 exactly how such mortality influences the total population of the fish 

 in the area. There is reliable evidence that intensive fishing reduces 

 the productivity of fishing effort in some cases, but there is also 

 evidence that by reducing competition fishing may produce faster 

 growth of the fish. The problem is worth some further discussion 

 since, besides its economic importance, it gives us an insight into the 



