Introduction. 



METHODS OF COMMERCIAL FISHERY. 



From a general standpoint all marketable sea fishes are 

 regarded as belonging- to one or the other of two classes, 

 viz.: Pelagic and Demersal. Broadly speaking Pelagic- 

 fishes are those that live at various depths, whereas 

 Demersal fishes spend the greater portion of their lives on 

 the sea bed. 



The pelagic species with \\hich \ve have to deal are not 

 numerous, but they comprise the Herring, Mackerel, 

 Sprat, and Pilchard, all of which are of the highest com- 

 mercial importance. These are often described as "drift- 

 fishes" on account of the fact that for a certain period of 

 the year they frequent the drift, or upper strata of the sea, 

 feeding largely upon the minute animal and vegetable 

 life to be found in such open water. Until of comparatively 

 recent years, the term "irawl fish " was applied solely to 

 demersal fishes, but nowadays, notably in the North Sea, 

 comparatively large numbers of Herring and Mackerel 

 arealso caught on the bottom by means of the trawl. During 

 the period of their inshore migration, however, pelagic 

 fishes are chiefly caught in " drift-nets," i.e., nets 

 suspended vertically from the surface of the water, in 

 which the fish become enmeshed behind the gill-covers in 

 swimming against the current, by means of ''seines," 

 i.e., nets operated in such a way as to enclose an observed 

 shoal, and by other less familiar methods. 



Demersal fishes, on the other hand, arc- caught com- 

 mercially almost entirely in two distinct ways, namely 

 trawling and long-lining. The trawl varies in size and 

 method of construction largely in accordance with the 

 type of vessel from which it is tised, but in general 

 principle it consists of a bag of netting, fitted with bridles 

 which enable the whole to be towed over the bottom bv 

 means of a single rope. The chief difference in construc- 

 tion lies in the method adopted for keeping the mouth open 

 tinder water. The smaller sailing craft are generallv 

 supplied with a "beam-trawl," in which this is effected bv 



