298 DREDGING AND TRAWLING 



As it is intended to scour the bottom, it is necessary 

 to make the foot rope heavy ; for medium-sized 

 trawls 8-inch rope is recommended, weighted by the 

 attachment of lengths of chain. 



The net should be about one and a half times the 

 length of the beam. It is made of hemp or manila 

 twine of 2 to 2j inch mesh in the back and belly, 

 and i inch double mesh in the cod end. The lower 

 part of the cod end, which comes in contact with the 

 ground, is protected from chafe by an extra piece of 

 stout netting attached on the outside. 



The trawl moves comparatively slowly over the sea 

 bottom, and consequently fish which have entered the 

 net frequently manage to swim out again and avoid 

 capture. To obviate this, pockets are formed by 

 stitching together the back and belly of the net at the 

 sides, as indicated in Fig. 202. The net is opened and 

 closed behind by a running string through the meshes. 



The 2 or 2j inch mesh is much too large to retain 

 any small organisms. The whole net may be lined 

 with sprat netting (i-inch mesh) or bags of the same 

 material and of mosquito netting may be attached to the 

 back, in the path of the swirl caused by the foot rope. 

 The latter system has the advantage that the coarser 

 part of the catch is kept in the trawl, while samples 

 of the smaller animals are separately collected and 

 saved from crushing. 



Tow nets with cane or iron rings and a long cheese- 

 cloth bag may also be attached to the beam or to the 

 net. If placed too far back, they frequently fill with 

 sand or mud, and burst. 



The very small makes of trawl, which are suited for 

 use from rowing boats or launches, are usually known 

 as " shrimp trawls." In these the net is made of stout 

 sprat meshing with a lining of mosquito net. 



