This paper reviews studies of relationships between riverine fish and woody
debris at micro- and meso-habitat scales, and discusses the potential
functions of instream structure for lowland river fish. Experimental research,
mainly in North America, has identified three main functions of woody debris
as microhabitat for fish in upland streams: overhead cover that decreases
predation risk both vertically and horizontally; horizontal visual isolation
that reduces contact between fish; and velocity refuge which minimizes
energetic costs. As with habitat features in other aquatic environments,
increasing spatial complexity of woody debris may modify predator–prey
interactions and provide greater surface areas for the growth of prey items.
Woody debris may also provide spatial reference points for riverine fish to
assist them in orienting within their surroundings. Lowland rivers differ from
upland streams in terms of a number of physical variables, including
turbidity, depth and water turbulence. Relationships between fish and woody
debris in lowland rivers are likely to rely on mechanisms different to those
in upland streams. Recent initiatives involving the reintroduction of woody
debris into previously cleared lowland rivers to replace lost fish habitat are
a positive development for lowland river restoration. However, if woody debris
reintroduction is to maximally benefit lowland river fisheries, there is a
requirement for better understanding of the ecological functions of woody
debris in lowland rivers.
Shining a light on the loss of rheophilic fish habitat in lowland rivers as a forgotten consequence of barriers, and its implications for management
