Fish spatial distribution in the littoral zone of Lake Pareloup (France) during summer

Abstract

We studied the spatial distribution of 11 fish species in the littoral zone of Lake Pareloup (South-West of France) using a non-destructive Point Abundance Sampling by Scuba diving. The fish spatial assemblage was investigated with seven commonly used environmental variables (topographical, biological and substratum variables). Three fish groups colonising three different habitats were identified. The spatial distribution of each fish species was mainly influenced by two environmental factors: distance from the bank (highly correlated with depth) and vegetation cover. i) Young-of-the-year (YOY) cyprinids and northern pike were mainly associated with a small distance from the bank (less than 6m). ii) Older cyprinids and perch (>/= 1+) were located between 6 and 12 m from the bank. iii) YOY perch and older northern pike (>/= 1+), occurred independently of the distance from the bank, but exhibited different responses to the percentage of vegetation cover: pike preferred areas with dense vegetation cover, while YOY perch abundance decreased rapidly with increasing vegetation cover. Thus, YOY fishes were common and abundant in shallow water, whereas large predators such as northern pike were found in vegetated areas. Therefore, vegetation cover, although generally considered as a crucial 0+ fish habitat, was here a secondary variable after distance from the bank. We hypothesised that the high density of predators (and especially northern pike) inside the vegetation as well as their high predation efficiency in this area could explain such a spatial distribution, shallow littoral areas being, in that case, safer from predation than vegetated ones for YOY fishes.