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Fish Information Table (39KB)

Processing Methods

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Sampling sites for fish collection are chosen to represent the set of environmental conditions deemed important for controlling water quality. The two types of sampling sites established are fixed sites and synoptic sites. Fixed sites are usually located near USGS gaging stations where continuous discharge measurements are available, and other physical and chemical characteristics can be measured. Three sampling reaches, sections of the stream designated as the sampling unit for describing fish community structure, are established to represent environmental conditions associated with each fixed site. Three reaches are the minimum needed to determine variability within the stream. Synoptic sites are usually nongaged sites where one-time samples are taken, and a limited number of physical and chemical characteristics are measured to answer questions regarding source, occurence, and spatial distribution. Only one sampling reach is required for synoptic sites.

The sampling season should occur during low- and stable-flow periods, usually mid-June to early October, when access to the stream and the suitability of wadeable stream sampling methods is maximized. Sampling efficiency tends to be greatest during this time period since fish populations tend to stay in the same area.

Electrofishing
Electrofishing is the use of electricity to capture fish. Towed electrofishing gear is used for sampling fish in wadeable streams. The power source is either a 24-volt deep cycle battery or a 115-volt gasoline-powered generator. Electrical current stuns the fish and draws them toward the anode, the positive end of the current.

Towed electrofishing, where a portable generator is placed in a boat and towed behind an operator, is done in streams greater than 1 m deep and 5 m wide. Electrofishing crews requires three to six individuals, with members either operating the electrofishing equipment, collecting fish with dip nets, or transferring fish to the holding container. Sampling begins at the downstream boundary of the sampling reach and is conducted in an upstream direction. This maximizes visability and collection efficiency.

Nonwadeable streams are sampled using electrofishing boats. These boats are usually made of aluminum and have a gasoline-powered generator and an electrical output control mechanism.

Seining
Seining is a technique for collecting small fish and complements electrofishing to obtain a representative sample. Seines are collection devices that trap fish by enclosing or encircling them. Seines consist of a mesh panel with weights on the bottom, floats at the top, and poles on each side. There are many dimensions for seines, but the most common sizes used are 3 x 1.2 m, 7.6 or 9.1 x 1.2 m, and 30.5 to 61 x 1.8 m. The smallest seine is known as a common sense seine while the 7.6 or 9.1 m seine is known as a bag seine, since it has a bag or packet in the center. Seining is usually done downstream where it is the most effective is collecting fish.

For the LIRB, seining was mostly conducted in wadeable streams. In wadeable streams relatively free from obstructions, the bag seine is used. In riffle areas, a common sense seine is used with a technique known as "kick seining." Two people hold the seine above the water, perpendicular to the flow. Then the poles and lead line of the seine are thrust to the stream bottom. A slight pocket in formed in the seine as the poles are allowed to slant downstream. A person, upstream of the seine, kicks the substrate as he or she works dowstream toward the seine. This is done across the channel, and then the seine is lifted out of the water and the fish removed.