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DESCRIPTION OF A RING NET AND A TRAP NET FOR THE SAMPLING OF PIKEPERCH FRY
DESCRIPTION D'UN FILET TOURNANT ET D'UN FILET PIEGE POUR LA CAPTURE D'ALEVINS DE SANDRE

by/par

Maria Nagieć
Wydzal Ochrony Wód i Rybactwa
Sródladowego, Olsztyn
Poland/Pologne

ABSTRACT

A ringnet and trapnet for the capture of pikeperch fry are described. The trapnets, particularly if lighted, are selective but because of their effectiveness and easy application are useful for studying the distribution of fry and its relative abundance in different years.

RESUME

On décrit un filet tournant et un filet piège pour la capture d'alevins de sandre. Les filets pièges, en particulier s'ils sont éclairés, sont sélectifs, mais, du fait de leur efficacité et de leur application facile, ils sont utiles pour l'étude de la distribution des alevins et de leur abondance relative au cours de différentes années.

CONTENTS

1. RINGNET

2. TRAPNET

1. RINGNET

The ringnet presented in the attached picture (Figure 1) was constructed of cotton netting of about 5 mm mesh size. A lead line was attached to the lower part of the net and a purse line passed through metal rings. Loading of the line was sufficient to keep the ringnet always at the bottom but then had the disadvantage that if the bottom was soft and muddy the net collected some mud and it was difficult to remove fish from the net. Consequently further catches with this gear were not carried out, although the results were rather good particularly in the case of pikeperoh fry.

All catches with ringnet were carried out at night.

2. TRAPNET

Experimental catches of pikeperch fry were carried out with trapnets, constructed as in the attached picture (Figure 2). The gear was always placed at the bottom at dusk, and taken out the following morning at dawn. Fishing was carried out in water 1–5 m deep. Nine trapnets were used; four of them were illuminated by an electric torch placed inside the gear. The torch was directed to the bottom so that it illuminated both throats. Trapnets were made of wire (5 mm in diameter) and steelon netting (dyed brown) of approximately 1 mm bar mesh. The gear was weighted with bricks. By adjusting the length of line holding the bricks, it was possible to place the traps at different depth. Each trapnet was equipped with polycele floats.

Trapnets were used during five consecutive nights, being placed at the bottom in the same place where pikeperch catches were carried out with a ringnet in 1961 and 1962 (Lake Jeziorak, Siemiany Bay, Mazurian Lake District).

Fry of the following species were obtained :

Perch (Perca fluviatilis) - 1 785 individuals
Ruff (Acerina cernua) - about 8 500 individuals
Pikeperch (Stizostedion lucioperca) - 166 individuals
Others (Cyprinidae) - 9 individuals

Preliminary results concerning the differences in fishing efficiency of illuminated and non-illuminated traps are presented in Table I.

TABLE I
Data on catches from lighted and unlighted trapnets
DateTrapnets lightedTrapnets unlighted
 SpeciesMean number
of fish in 1 trap
SpeciesMean number
of fish in 1 trap
27.VIPeroh292.7Perch-
Ruffca           40               Ruffca 2    
Pikeperch     1.75Pikeperch-
Others-Others-
28.VIPerch21.25Perch-
Ruffca      250                  Ruffca 1    
Pikeperch11.0Pikeperch-
Others  0.8Others-
29.VIPerch5.50Perch-
Ruffca         1 390                        Ruffca 1    
Pikeperch-Pikeperch-
Others     1.0Others-
3.VIIPerch109.0Perch   0.6
Ruffca         350               Ruff-
Pikeperch26.0Pikeperch-
Others-Others-
4.VIIPerch16.75Perch-
Ruffca         1                Ruff-
Pikeperch   2.75Pikeperch-
Others-Others-

Figure 1

Figure 1 Ringnet

Figure 2

Figure 2 Trapnet


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