Electrofishing results corrected by selectivity functions in stock size estimates of brown trout (Salrno trutta L.) in brooks

Abstract

To overcome the problems usually met as a consequence of small numbers of fish collected for trout stock size evaluation in small rivers, a selectivity function was developed and tested in two small rivers in western Switzerland. The function takes the form In E = bL-k whereEis the fishing efficiency, L is the fish length in cm, k is a constant and b is the slope, estimated by regression analysis.A good fit was obtained f o r k = 1 (R. Flon de Carrouge) and k = 2 (R. Cerjaule). Individual selectivity functions have to be computed for each survey, because they depend on the operators of the fishing gear and on the physical and biological conditions in the rivers.The results are discussed in the light of the Petersen mark-recapture method and the De Lury removal method for stock evaluation. The mark-recapture method gives better results when time intervals between successive fish removals are short.

An Analysis of Potential Stream Fish and Fish Habitat Monitoring Procedures for the Inland Northwest: Annual Report 1999.

“…Previous investigations have attempted reduce the influence of sampling bias by using a variety of maximum effort methods, such as multiple removal ("depletion" sampling) and mark and recapture methods. However, these techniques are also influenced by factors such as fish size, morphology, and behavior as well as the physical habitat characteristics of the area sampled (Buttiker 1992;Rodgers et al 1992;Anderson 1995). To minimize the influence of fish sampling efficiency on data quality, future effectiveness monitoring protocols should incorporate fish sampling methods with known biases and apply them under circumstances in which catchability is reliable.…”

Risk management of non-target fish taxa in the Yakima River Watershed associated with hatchery salmon supplementation

“…In the last stage, only when a causation analysis indicates impacts to NTT are beyond acceptable levels does a risk containment measure become initiated. In this case, risks to NTT are contained by implementing an adaptive management action to reduce or eliminate impacts reasonable ways of indexing relative abundance because fish size is one of the most important factors that influences electrofishing efficiency (Buttiker 1992;Anderson 1995).…”

Selecting Gear for Monitoring Fish Assemblages

“…Yeh 1977;Dauble & Gray 1980;Layher & Maughan 1984;Schramm & Pugh, Chapter 4), and developed adjustment factors so that corrected estimates may reflect existing assemblages (e.g. Hamley 1975;Willis et al 1985;Buttiker 1992;Spangler & Collins 1992). In spatial and temporal monitoring programmes, focusing on relative differences and trends or change rather than on unbiased estimates (Willis & Murphy 1996) often circumvents selectivity.…”