Comparison of two point abundance sampling methods to assess young roach (Rutilus rutilusL.) microhabitat in the littoral zone of lake Pareloup (France)

Abstract

One of the most frequently used sampling methods used in defining fish microhabitat is the Point Abundance Sampling by Electrofishing (PASE) technique. Nevertheless this method is size-selective and induces escapement behaviour in most fish species. The aim of this study is first to describe a direct visual fish observation method, the Point Abundance Sampling by Scuba diving (PASS), and second, to compare this method with the classical PASE to determine 0+ (i.e. young of the year) roach (Rutilus rutilus,L.) microhabitat in the littoral zone of a mesotrophic lake.The study was undertaken during summer 1998 in lake Pareloup (south-west France). Sampling was performed weekly in two restricted littoral areas of the lake which presented the same environmental and topographical characteristics aiming to compare 0+ roach habitat features obtained using the two sampling techniques (PASE and PASS). The two data matrices obtained (i.e. PASE and PASS) were used to develop microhabitat preference indices for each of the 9 variables as a measurement of habitat use by the 0+ roach vs. habitat availability.Even though 0+ roach occurrence and abundance were found to be similar with both methods, microhabitat profiles revealed different patterns. A significant microhabitat difference between the two sampling methods was found using the non-parametric statistical test of Wilcoxon (Z = -4.20, p < 0.01). We can hypothesise that the differences observed between the two sampling designs were due to an escapement behaviour of 0+ roach. Unlike PASS, using PASE, fish are located in «shelter habitats» such as shallow water and dense vegetation. Such behaviour is caused by the environmental disturbance induced by this sampling method. The study reveals that PASS appears to be more suitable than PASE for the assessment 0+ fish microhabitat. L'étude a été menée durant l'été 1998 dans le lac de Pareloup (France). L'échantillonnage a été réalisé dans deux zones littorales du lac présentant les mêmes caractéristiques environnementales de manière à comparer l'habitat obtenu avec chacune des deux techniques d'échantillonnage (PASE et PASS). Les deux matrices de données (PASE et PASS) ont été utilisées pour déve-lopper des indices de préférence du microhabitat pour chacune des 9 variables environnementales prises en compte. Alors que les deux méthodes donnent des valeurs identiques d'occurrence et d'abondance des gardons 0+, les profils de microhabitat révèlent des tendances différentes. En effet, une différence significative entre les profils obtenus par chacune des deux méthodes est révélée par le test non-paramétrique de Wilcoxon. Nous pouvons formuler l'hypothèse que les différences observées sont dues à un comportement de fuite du gardon 0+ face à l'une des méthodes d'échantillonnage. Contrairement aux résul-tats obtenus par PASS, par PASE, les poissons sont localisés dans des «habitats refuges», tels que les eaux peu profondes ou couvertes d'une dense végétation aquatique, conséquents d'une perturbation environnementale causée par cette mé...

A Comparison of Point Abundance and Continuous Sampling by Electrofishing for Age‐0 Fish in a Channelized Lowland River

“…Several studies have already directly compared point sampling with other methods of sampling age-0 fish. For instance, point sampling has been compared with seining (Garner 1997;Cowx et al 2001), scuba diving censuses (Brosse et al 1999), and electrofishing within stop nets (Perrow et al 1996). However, little is known about differences between point and continuous sampling strategies.…”

Inter‐calibration of three electric fishing techniques to estimate 0+ juvenile fish densities on sandy river beaches

“…In DE (Persat & Copp 1990), the operator activates the anode via a deadman's switch before submerging the anode in the water and keeping it motionless for a pre‐determined period of time. The presence of the operator can, however, disturb the fish (Brosse, Gabas, Cever & Lek 1999) and may reduce efficiency. The effect of the operator's presence can be decreased by increasing his distance from the sampled area, either by fastening the anode to an extension pole or by using an alternative technique (e.g.…”

“…population density, body size, behaviour of fish) and abiotic (e.g. conductivity, water temperature, substrata type) factors that may influence efficiency of electric fishing (Regis, Pattee & Lebreton 1981; Zalewski & Cowx 1990; Scholten 2003), while others have compared PAS by electric fishing with seine netting (Garner 1997; Cowx, Nunn & Harvey 2001), SCUBA diving censuses (Brosse et al. 1999), electric fishing within stop nets (Perrow, Jowitt & Zambrano González 1996) and continuous electric fishing (Pretty, Harrison, Shepherd, Smith, Hildrew & Hey 2003).…”