Fish Sampling 135 



position by stakes or weights."*^ Wing nets are sometimes fished with a 

 long lead net set upright between the wings at the net opening. This lead 

 net acts as a "drift" fence and fish following it soon find themselves in 

 the wing net. 



Hansen ^^ found considerable variation in the catch of wing nets at 

 various times of the year and under varying physical and chemical con- 

 ditions associated with water— temperature, turbidity, dissolved oxygen, 

 and carbon dioxide. 



Trap nets are usually modified wing nets with wings arranged in loops 

 to direct fish toward the opening of the net no matter which way they 

 attempt to go, and with a lead net attached inside a forebay so that fish 

 following the lead net to its proximal end are already inside of the front 

 of the trap. 



Mesh covering these nets is composed of nylon or cotton webbing 

 squares varying in size from M inch to 4 inches. Hoop diameters range 

 from 2/2 to 6 feet. Trap nets of larger sizes are not used for sampling. 



"Hoop nets" made of hardware cloth are more useful for fishing in 

 ponds and small lakes than are hoop nets or wing nets made of string 

 because the wire nets are not subject to muskrat damage. The nets are 

 constructed of /2-inch hardware cloth and consist of a cylinder of wire, 2 

 feet in diameter and 4 or 5 feet long, with a single funnel leading into the 

 open end and wire mesh across the closed end. Fish are removed through 

 a small door covering an opening on one side, or through the open end 

 of the cylinder after the funnel has been lifted out. 



Thompkins and Bridges ^^^ found that low doses of copper sulfate 

 (0.15 ppm) in soft water irritated the fish and caused them to move about, 

 thereby increasing the catch of wing nets set in the area of treatment. 

 Some fish may be attracted into a net by bait ^' -^ or by the darkness of 

 the water inside of it. However, other fish, that avoid nets of small mesh, 

 will enter those of larger mesh because their interiors are scarcely darker 

 than the surrounding water. Certain kinds of fish such as largemouth 

 bass will seldom enter hoop nets, wing nets, or trap nets in clear water, 

 whether the mesh size is large or small.^^ Because these nets are attractive 

 to certain kinds of fish and are avoided by others, the nets are extremely 

 selective and samples of fish taken by them will not be representative of 

 the fish population from which they were taken. 



Minnow Seine Sampling. Minnow seines are often used to catch the 

 young of various kinds of fish in order to gather information on the 

 number of species of fish present in a body of water and to determine 

 spawning success (relative abundance of young) of the several kinds of 

 fish present. Usually when a dominant year class of one species of fish 

 has been spawned, it will show up almost at once in early summer minnow 

 seine hauls. 



