302 • DREDGING AND TRAWLING 



considerably, and this may be conveniently done by 

 winding chain around the iron beams. The net should 

 be of " shrimp " or " sprat " mesh. The Agassiz 

 trawl is more useful for catching invertebrates than 

 for fish. The procedure in shooting and hauling does 

 not differ in any essential way from that already detailed 

 under " Dredging " (pp. 292-295). 



The Otter Trawl. — For work on small steamboats, 

 especially where a winch or capstan of any kind is 

 available, a small otter trawl is more handy to use than 

 a beam trawl of equal spread. The shape of the net 

 of an otter trawl is practically the same as that of a 

 beam trawl, the difference between the two trawls 

 consisting in the method adopted for keeping the 

 mouth of the net open. In the case of the beam trawl 

 this is effected by the long wooden beam and the two 

 iron heads. In the case of the otter trawl two oblong 

 boards, fitted with iron shoes — the otter boards — are 

 used. The mouth of the net in both beam and otter 

 trawl has a heavy ground rope below, which drags 

 along the sea bottom, and a head line above, which in 

 the beam trawl is attached to the beam, but in the 

 otter trawl is floated up in the water by means of corks 

 or (in deep water) glass floats attached to it. These 

 two ropes, the head line and the ground rope, are made 

 fast at each end to the hinder ends of the oblong otter 

 boards, which, when the net is working, stand on their 

 lower iron-shod edges on the sea bottom. 



The two otter boards act after the manner of kites 

 which are " flown " from the stern of the ship by 

 means of two towing warps, one bearing away to star- 

 board, the other to port. Each towing rope is fixed 

 to its otter board by means of iron brackets or of four 

 chains, in such a way that the point of attachment is 

 behind the centre of the board, and the board therefore 



