Catch-effort Efficiency using Three Small Seine Nets

Abstract

A catch‐effort method of estimating fish density and biomass using three small seine nets placed simultaneoulsy to enclose a known area of water is described. The efficiency of capture in the first catch was high for both density and biomass with an overall average of 70 and 69% respectively, and 95% confidence limits of approximately 20% for both.

Species density obtained for fish sampled with three seine nets hauled individually towards a stop net or a bank

“…Sampling procedures with identical three seine nets hauled individually towards a stop net or a bank were described and presented in figures and photos in former papers (Penczak & O'Hara 1983, Frankiewicz et al 1986, Penczak et al 1997, Penczak & O'Hara 1998. For the density calculation, the Zippin model was applied in the above papers Photo 1.…”

“…After laying all three nets on the bank they were drawn simultaneously into the water to form closed semicircular areas. Each net was then alternately hauled back onto the bank (Penczak & O'Hara 1983, Frankiewicz et al 1986, Penczak et al 1997 or on the stop net (Penczak & O'Hara 1998). Modifications with net dimensions and sampling techniques were related to sampled water bodies, and detailed descriptions are available in the four cited papers.…”

“…We used the TSNT sampling technique in the Weaver River (England), the Ivai River (Parana), the heavily trafficked Shropshire Union Canal (England), and the littoral part of the Sulejów Reservoir (Poland) (Penczak & O'Hara 1983, Penczak et al 1997, Penczak & O'Hara 1998, Frankiewicz et al 1986). For the above research, we used small mesh (1.5 -4.0 mm) knotless netting material.…”

“…However, in their study based on 82 literature references, the authors do not indicate any work providing a method that enables the confidence interval to be calculated for an assessment of juvenile fish density using a net, other than the variable mesh seine method, which supplies a solution for only a specific case of the problem. The first to have addressed and solved this problem are Penczak & O'Hara (1983). They applied a three seine nets technique (TSNT), which consists in nets placed simultaneously and submerged one after the other.…”

“…As three samples are an absolute minimum for any accurate estimate employing a removal technique (Raleigh & Short 1981), this procedure provides an estimate of density with a known error because it allows for calculations of the variance value for calculated density. We used the TSSN sampling technique in two rivers (Penczak & O'Hara 1983, Penczak et al 1997), a heavily trafficked navigation canal (Penczak & O'Hara 1998), and the littoral part of a reservoir (Frankiewicz et al 1986). In all of the conducted catches the efficiency of the first catch was in the range 100-60 (40)% in relation to the calculated density (Table 1), despite some obstacles (branches, trunks, submerged plant clumps, stones).…”