– We compared fish microhabitat use patterns in the littoral zone of a lake using a new direct method (point abundance sampling by scuba, PASS) and the widely used point abundance sampling by electrofishing technique (PASE). We collected microhabitat data for age 0+ roach (Rutilus rutilus L.), perch (Perca fluviatilis L.), and pike (Esox lucius L.). The two methods yielded different results for fish assemblage structure and microhabitat patterns. Using PASE, fish were mainly found in “shelter habitats” such as shallow waters and dense vegetation. It is likely that this behavior is caused by the disturbance of the observer stamping around. Using PASS, fish escapement behavior was rarely observed. Therefore, we concluded that this direct and nondestructive sampling technique can be used to provide an accurate microhabitat estimation of a fish community and is assumed to be more suitable than PASE for fish habitat studies.

No 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...