Animal perception in gravel-bed rivers: scales of sensing and environmental controls on sensory information

Animals make decisions based on the sensory information that they obtain from the environment and other organisms within that environment. In a river, this information is transported, transmitted, masked, and filtered by fluvial factors and processes, such as relative roughness and turbulent flow. By interpreting the resultant signals, animals decide on the suitability of habitat and their reaction to other organisms. While a great deal is known about the sensory biology of animals, only limited attention has been paid to the environmental controls on the propagation of sensory information within rivers. Here, the potential transport mechanisms and masking processes of the sensory information used by animals in gravel-bed rivers are assessed by considering how the physical nature of sensory signals are affected by river hydromorphology. In addition, the physical processes that animals have the potential to directly perceive are discussed. Understanding the environmental phenomena that animals directly perceive will substantially improve understanding of what controls animal distributions, shifting emphasis from identifying correlations between biotic and abiotic factors to a better appreciation of causation, with benefits for successful management.