Looking through a dirty glass: how different can the characterization of a fish fauna be when distinct nets are used for sampling?

Gianfranco Ceni,João Paes Vieira

doi:10.1590/s1984-46702013000500005

Abstract

The present study compares fish species composition, dominance, and size-structure patterns at an open sand beach area (32°15'S, 52°46'W) in Mirim Lake, RS, Brazil, estimated from samples collected with two distinct beach seine nets. The BS-9m net is 9 m long and 1.5 m high, and is made with a 5 mm multifilament mesh on its central portion and 12 mm on the side wings. The BS-30m net is 30 m long and 1.8 m high, with a 12 mm monofilament nylon mesh all over the net, except for a 30 cm strip made with a 12 mm multifilament mesh on the lower portion. Thirty hauls were performed with both nets resulting in a total of 849 fish captured, comprising 34 species. BS-9m was selective for individuals smaller than 60 mm TL and BS-30m for individuals larger than 60 mm TL. Low values of the faunal similarity (JI = 0.41, ANOSIM R = 0.2309, p < 0.0001) and numeric dominance (PSI = 0.46) indexes were revealed. We suggest that the concurrent use of both samplers provide a better description of the fish fauna of shallow areas. However, due to their robustness, rusticity, and ease of use and maintenance, small multifilament seines are indicated for regular work in environments without obstacles and with little open sand area available for sampling.

Highlights

The great variety of beach seines reported in fish fauna characterizations in the literature hampers a comparison between distinct studies
One important element of beach seines, their size, was tested by MONTEIRO-NETO & MUSICK (1994), who concluded that there is a direct relationship between the size of a net and the number of fish it catches: larger nets retain a greater number of individuals because they sample a larger area
A variety of beach seine nets have been reported in publications, contrasting with the fewer numbers of studies comparing their performances in marine (MONTEIRO-NETO & MUSICK 1994), estuarine (STEELE et al 2006) and freshwater environments (DELACY & ENGLISH 1954, RÍHA et al 2008)

Summary

Introduction

The great variety of beach seines reported in fish fauna characterizations in the literature hampers a comparison between distinct studies. Differences in the composition of catches when different samplers are used have been studied by several authors (HAYES 1989, GROWNS et al 1996, ROZAS & MINELLO 1997, BRIND’AMOUR & BOISCLAIR 2004, CLAVERO et al 2006, ERÖS et al 2009), and only direct comparisons among sampling gears can clarify the advantages and disadvantages of each and the sampling bias they produce (GROWNS et al 1996, OLIN et al 2009) For this reason, we endeavored to compare, in the present work, species composition, numeric dominance, and size structure of fish captured with two beach seines that have distinct structural characteristics

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