54 



Lattin: Introduction 



Intro, fig. 76. Surber square-foot bottom sampler being 

 used in shallow stream. 



Heavy-duty dredging under all types of bottom 

 conditions is done with a Peterson dredge in which 

 the mechanism holding the jaws open on the way down 

 is released when it touches bottom. This dredge is 

 much heavier than the Ekman, often weighing up to 

 70 pounds, so a sturdy winch is required to operate it. 



The Surber square-foot bottom sampler (intro. fig. 

 76) is designed for use in riffles of shallow streams. 

 It consists of two square frames hinged together. 

 One bears the net that extends downstream and the 

 other delimits the area of bottom to be sampled. 

 The frame is placed in position on the bottom and 

 the enclosed pebbles or other material are carefully 

 gone over with the hands to dislodge the specimens. 

 The insects are carried back into the net by the 

 current. This sampler has the disadvantage of per- 

 mitting some specimens to escape around the edges, 

 especially if a fine mesh net is used. Side wings 

 are used to reduce this hazard. One great advantage 

 of the Surber sampler is that the frames fold flat and 

 can be easily carried in the field. 



The Hess sampler (intro. fig. 77) is a variation of 

 the Surber sampler designed to correct its disadvantage 

 of allowing specimens to escape. It is a cylinder of 

 one-half-inch hardware cloth on a steel frame. The 

 hardware cloth is covered except on the front to keep 

 the smaller organisms from escaping. A square hole 

 is cut in the back and a net attached. The sampler 

 is placed on the bottom and is turned by the handles 

 until it is firmly imbedded in the bottom. The tech- 

 nique of collecting is the same as for the Surber 

 sampler. When using either of these samplers in 

 rapid water, the operator should stand downstream 



from the sampler, bracing it with his legs, to prevent 

 its movement by the current. The standard Surber 

 sampler and the improved Hess sampler are limited 

 in usefulness to depths of less than arm's length. 



A more versatile sampler was devised by Usinger 

 and Needham (1956) (intro. fig. 78). This drag-type 

 sampler consists of a rectangular iron box with bars 

 on the open face to exclude large rocks and trash. 

 The two leading edges are provided with tines that 

 dig into the rock and gravel of the bottom. The curved 

 tines serve the same purpose as the fingers of the 

 operator of the shallow-water type samplers. The 

 current sweeps the organisms into the net, just as in 

 those samplers. The net bag is removable and can be 

 opened by means of a zipper to gather the organisms. 

 A canvas sleeve is provided for the protection of the 

 net. In operation the sampler is lowered into a riffle 

 and pulled. The area of bottom to be sampled is 

 determined by the length of bottom over which it 

 is pulled. 



The square-foot tray ("basket method," Wene and 

 Wickliff, 1940) may be used to determine the number 

 and type of organisms per unit area on the bottom of 

 a stream or lake. The tray is made with wooden sides 

 and a one-fourth-inch mesh screen bottom. It is filled 

 with clean bottom material. It is then placed flush 

 with the surrounding bottom of the stream or lake 

 and should be left long enough for the fauna to become 

 stabilized. A collar is placed around the tray at the 

 time of removal to avoid disturbing the organisms. 

 The trays are lifted out at intervals and all the 

 organisms collected and counted. 



Traps. — Several traps have been devised which 



Intro, fig. 77. Hess sampler, collecting technique. 



