THE BEAM TRAWL 295 



the dredge inboard, it is advisable to keep the frame 

 slung up, and if necessary lashed, until the contents 

 of the bag have been emptied. 



Trawling. 



Trawling is the best and easiest way of obtaining 

 extensive samples of the bottom fauna, but the method 

 can only be satisfactorily employed on smooth ground. 



Three types of trawl are available for biological 

 investigation — the beam trawl, Agassiz trawl, and 

 otter trawl. 



The Beam Trawl.— In this pattern the net is kept 

 open horizontally by a long beam of greenheart or 

 oak, and vertically by a pair of iron runners or heads, 

 Fig. 202 gives a good idea of the appearance of the 

 frame. 



Beam trawls may be used at practically any depth, 

 but in very deep water they show a tendency to capsize, 

 the beam dragging along the bottom, and the foot rope 

 completely closing the net. In such cases the haul is 

 naturally a complete failure. With a certain amount 

 of experience in shooting this difficulty may be largely 

 overcome ; but the otter and Agassiz trawls will be 

 found more efficient for work in greater depths than 

 300 fathoms. 



The beam trawl collects a larger number of inverte- 

 brates than the otter trawl, but does not secure so 

 many fish — active species of the latter are doubtless 

 scared by the beam in its passage along the bottom. 



Trawls of this pattern range from 6 to 50 feet in 

 beam-length. Small makes, with a 6 or 8 feet beam, 

 are easily handled from a rowing boat or launch. 

 The commercial beam trawl is usually from 40 to 

 50 feet in length ; these sizes are, however, unwieldy, 



