has proven to be the most effective in collecting fish. Three bag seine hauls are conducted in the sampling reach, each covering an area of about 50 m, and taken from the upper, middle, and lower sections of the sampling reach. The fish from the three seine hauls are combined and processed before immediate release.
Nonwadeable streams can be sampled using a beach seine in wadeable shoreline areas, if present. Three beach seine hauls are conducted in accessible parts of the upper, lower, and middle sections of the nonwadeable sampling reach, the length of each equ aling that of the seine. The fish from the three seine hauls are combined and processed before release.
Other sampling methods may be necessary to obtain a representative sample of the fish community for NAWQA. These methods include gill netting, using experimental gill nets, and hoop netting. Experimental gill nets 1.8 m deep with six sections of monof ilament mesh 7.6 m long each, using 13-, 25-, 38-, 51-, 76-, and 102-mm mesh sizes (bar measurements), can be used to collect a representative sample. Two experimental gill nets are set for each nonwadeable sampling reach.
Hoop nets should be constructed of fiberglass hoops 0.6 m in diameter, with funnels on the second and fourth of the seven hoops, untreated 38-mm mesh (bar measure), and should be 3.7 m long. Two hoop nets are set within the sampling reach. Hoop nets should be baited with cheese, pressed soybean cakes, or other material and set in the water along a steep bank or on the outside bend of the stream parallel to the current with the opening facing downstream.
During sample processing, carbon dioxide is used to anesthetize the fish and thereby minimize handling stress. Taxonomic identification is made only by an ichthyologist who is familiar with the taxonomy of fish species found in the study unit. Both total and standard length measurements are made, and the data are recorded to the nearest millimeter; weight is recorded to the nearest gram. The presence of external anomalies, including skeletal deformities, eroded fins, lesions, tumors, diseases, and parasites, is also recorded.
The fixing and preserving of specimens are required for those fish that
cannot be taxonomically identified in the field and for voucher specimens
(representatives of nongame species collected from each sampling reach).
Fixing fish tissues is achieved by using
10-percent buffered formalin. Permanently preserving fish specimens
requires storage in
40-percent isopropyl alcohol or 70-percent ethanol.
The USGS Branch of Analytical Services' Biological Quality-Assurance Unit located at the National Water-Quality Laboratory provides verification of taxonomic identifications through the collection of voucher specimens and the establishment of a reference collection. At each sampling reach, voucher specimens are collected, fixed, and preserved to document and verify species identification.