guidelines for safe operation of electrofishing equipment are discussed by Reynolds (1983) and Goodchild (1991).
Seining is a common method for sampling fish communities in streams (Bagenal, 1978; Nielsen and Johnson, 1983) and is used to complement electrofishing collections in order to obtain a representative sample. Although electrofishing is viewed as the most effective single method for sampling fish communities in streams (Bagenal, 1978; Plafkin and others, 1989), it is reported to be size selective, with large fish more susceptible to capture than small ones (Wiley and Tsai, 1983). Therefore, electrofishing alone should not be used to assess fish community structure (Reynolds, 1983). Unlike electrofishing, seining is an effective technique for collecting small-size individuals and should be conducted following electrofishing to complement electrofishing collection efficiency and obtain a representative sample.
Seines are collection devices that trap fish by enclosing or encircling them. The fish are then sieved from the water by means of mesh panels. The bottom or lead line has lead weights strung or crimped onto it to weight the net. The top or float line includes cork, polystyrene foam, or plastic floats to keep the top of the seine near the water surface. The net is attached to wood or metal poles to handle the seine.
Seines are manufactured in a variety of dimensions and mesh sizes. However, three types of seines are commonly used to study fish community structure: (1) 3 x 1.2 m, (2) 7.6 or 9.1 x 1.2 m, and (3) about 30.5 to 61 x 1.8 m. The 3- x 1.2-m seine is referred to as a "common sense" seine (Hendricks and others, 1980; Bryan, 1984) and is attached to two wooden poles 31.8 mm in diameter. A mesh size of 6.4 mm is appropriate for the common sense seine. The 7.6- or 9.1-m seine has a bag or pocket in the center of the seine and, thus, is referred to as a bag seine. As the bag seine is pulled through the water, fish are herded toward the center of the net and into the bag.
As with the common sense seine, a bag seine is attached to two 31.8-mm diameter wooden poles and usually has a mesh size of 6.4 mm. A beach or drag seine is typically used along the shorelines of large bodies of water and is usually greater than 30 m lo ng. Because of the greater length, a larger mesh size (9.5 mm) and larger dimension poles (usually 51 mm x 51 mm) are required for the beach seine to maximize sampling efficiency and seine durability.
Wadeable streams are sampled by seining using the common sense seine, the bag seine, or both. The choice of the method used is dependent on the geomorphic channel units present and the degree of complexity of the habitat features within a sampling reach. Riffle areas require a seining technique separate from that used in runs or shallow pools. Large areas of submerged objects make seining difficult, and the potential for collecting a representative sample should be evaluated before seining in an area with submerged objects.