Effects of sedimentation on an endangered benthic fish, Cobitis shikokuensis: is sediment‐free habitat a requirement or a preference?

Abstract

A negative correlation between the degree of fine sediment deposition and the abundance of stream benthic fishes has often been reported, although the causal mechanisms for this effect are not fully understood. To better understand the influence of sedimentation, it is important to clarify whether it alters the habitat required by fish, or merely preferred by them. We conducted two enclosure experiments in the field to examine (i) whether an endangered benthic fish, Cobitis shikokuensis, prefers sediment‐free substrate and (ii) whether fine sediment deposition has negative effects on the physiological condition of C. shikokuensis. The first experiment, which used three types of substrates, ‘cobble’, ‘pebble’ and ‘mixture of fine sediment and pebbles’, showed that C. shikokuensis avoided the mixture. The second experiment, which compared the physiological condition of fish reared in enclosures with either a pebble or mixture substrate, showed that the condition of the fish in the latter group declined more quickly. These results suggest that, for C. shikokuensis, sediment‐free substrate is a habitat requirement, not merely a preference, and that excessive input of fine sediment due to human activities can cause a decline in the population of this species.

Size-Specific Advantage in Shelter Competition Between the Mountain Madtom and Crayfishes

“…As human development continues to sprawl into previously isolated environments, issues such as nonnative species introductions and agricultural runoff tend to follow (Holdich 1999;Wang et al 2001;Helms et al 2005;Bar-Massada et al 2014). For benthic fishes, these factors can pose a greater threat when sediment settles to the river bottom, filling in interstitial spaces and embedding larger rocks beneath which prey live, eggs are laid, and shelter from predators is found (Kawanishi et al 2015). Additionally, the introduction of large, aggressive crayfishes has been associated with native fish population declines, extirpations, and extinctions (Twardochleb et al 2013).…”