The experimental gill net must be rigged with anchors on the lead line at both ends of the net, and buoys at the float line at both ends of the net. Also, the net must be tagged with some type of identification to indicate ownership. If the net is set (suspended in the water column) perpendicular to the shoreline, one end of the float line should be attached to the shore. The length of rope attaching the anchor to the lead line should be long enough so that the lead line of the net is resting on the stream bottom. However, if conditions do not permit a gill net set perpendicular to shore (high-water velocity carrying debris that could damage the net or reduce sampling efficiency), then the net should be set parallel to the current. The gill net set depends on flow conditions and procedures used by local fish ecologists.
The net should be set in the late afternoon and remain in the water for a period of several hours but no longer than 24 hours. The number of fish collected in a gill net is not linearly related to the duration of the set (Hubert, 1983). The exact duration of the set to achieve the maximum catch depends on flow conditions and the presence of drifting debris. Additional considerations concerning the duration of the set are high water temperatures (accelerating decomposition of fish that may die in the gill net) and State regulations that may restrict the duration of the set. The decision concerning the duration of the set should be made after consultation with local fish ecologists.
Two experimental gill nets are set for each nonwadeable sampling reach. Each experimental gill net should be located within the sampling reach where it would be (1) most effective in collecting a representative qualitative sample, (2) least likely to b e damaged from snags or debris, (3) least likely to present a hazard to the public, and (4) least likely to be vandalized.
Hoop netting is the capture of fish by entrapment in an enclosed mesh trap. It has many of the advantages and disadvantages of gill netting; however, unlike gill netting, fish caught by hoop netting can be released with little or no harm to the fish.
Hoop nets are cylindrical traps that are fished passively in moderate or low velocities. They are usually constructed of nylon mesh hung on round frames (hoops) made of steel, fiberglass, wood, or flexible plastic pipe and have one or more funnel-shaped throats inside the net to retain the catch (fig. 4). Hoop net mesh sizes vary from 12.7- to 101-mm bar mesh, strung on hoops that vary from 0.3 m in diameter to 2.4 m, or greater. The mesh can be chemically treated to increase the durability of the hoop net. Though hoop nets are selective for certain species, they often collect species not caught by other gear. Some fishes that avoid or are not susceptible to gill netting, seining, or electrofishing can be captured with hoop nets (Hubert, 1983).