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Casselman, J. M., T. Penczak, L. Carl, R. H. K. Mann and J. Holcik (1990). An evaluation of fish sampling methodologies for large river systems. Polskie Archiwum Hydrobiologii. 37:521-551.

Fish sampling methodologies for large rivers were reviewed at the Large River Symposium by surveying 64 diverse sampling methods, their application and efficiency under various riverine conditions, diversity of habitat, and extreme environmental conditions in large rivers. Fishways and fish ladders are uniquely applicable for sampling migrating fish in rivers, especially those with large control dams or high flows. Remote sensing by stationary hydroacoustics has been used where spawning migrations are assessed. Trawling may be used where the current is relatively slow. There are no standardized sampling techniques for large rivers because environmental conditions are often extremely variable. Usually attempts are made to sample selectively only those parts of the river that have low flow and are amenable to bottom-set stationary gear such as gill nets, trap nets, and other fixed gear. Sampling riverine fishes at the community level is much more difficult and requires combining the results of several types of sampling gear (e.g., quantitative sampling using electrofishing or explosives, in combination with large lift nets or block off nets). Portable fish diversion systems exist that could make fish sampling in large rivers much more efficient. Some of these systems, such as portable marine fences, weak electric fields, bubble currents, and hydrosonic pulsers could be used to direct and concentrate fish to improve the actual sampling procedure. Because environmental conditions are more variable in rivers than in lakes, it is essential that if sampling efficiencies are to be compared, environmental conditions must be the same. Sampling of fish populations in rivers where discharge is variable should be conducted in relation to velocity, rather than at fixed stations.