SEA-FISHERIES LABORATORY. 343 



on several other occasions, and shows that the vertical 

 closing nets, even when more than one haul is made, may 

 miss many of the species present. These various examples 

 will suffice to show that vertical hauls do not give such 

 truly representative samples as has sometimes been 

 supposed, that results taken from a few hauls only may 

 be deceptive, and that it is advisable to check the 

 accuracy by taking duplicate observations whenever 

 possible. 



Necessity for Frequent Vertical Hauls. 



It has sometimes been said that if vertical hauls be 

 taken from the bottom to the surface, they are bound to 

 show everything that is present in the area, and to 

 represent each constituent of the plankton in its true 

 proportion. It has been argued that while the surface 

 plankton may vary greatly, and therefore the surface nets 

 may give partial or deceptive samples, the various groups 

 of the plankton, however much they may rise or fall or 

 segregate into zones, must always be somewhere between 

 the bottom and the surface, and therefore must all be 

 sampled by a vertical haul. That may be the case in many 

 localities, but it is not necessarily the case always. It 

 must be remembered that some groups of organisms move 

 not merely up and down, but also laterally, so as to reach 

 and occupy some narrow gulley or some deeper hole, and 

 in that case a vertical haul might capture that particular 

 group of organisms or might escape doing so, and even a 

 small series of vertical hauls might, through this segrega- 

 tion, which is horizontal as well as vertical, give quite a 

 deceptive impression of the constitution of the plankton. 

 This possibility is exemplified in the accompanying 

 diagram, which represents a section across a fjord or sea- 

 loch with an irregular bottom having a ridge at E, a 



