River landscapes provide a spatially complex and temporally dynamic habitat that animals have to respond to at a range of scales to survive. I am interested in the direct linkages between organisms and their environment and, in particular, the physical processes that animals use to make informed decisions about their activity and presence. 

Tracking signal crayfish movements using radio-telemetry
I have used radio-telemetry (Passive Integrated Telemetry [PIT] tags) to track the movement of signal crayfish (Pacifastacus leniusculus), an internationally important invasive species, through river reaches in Lincolnshire and Northamptonshire, in collaboration with Prof. Stephen Rice, Prof. Ian Reid and the Environment Agency. Crayfish were found to be highly nocturnal and their activity was strongly related to the water temperature and depth of flow, moving less in cold weather and during high flow events. However, the relationship between environmental conditions and crayfish activity was not simple or linear, instead environment conditions acted as limiting factors to the movement of crayfish and were best described using quantile regression. 

Using sensory ecology to inform animal-environment interactions in rivers
Animals have an arsenal of sensory organs and can obtain detailed information about their environment and the presence of other organisms. Animals use this information, including sight, sound, touch, smell, taste and electrical and hydrodynamic senses, to make informed decisions within environments. The processes and the scale of processes animals can perceive does not match our scale of understanding, which tends to be focused at much coarser scales. In a recent review (Johnson and Rice, 2014), we argue that quantifying environmental processes at the scale of the sensory organs of animals would increase our understanding of the links between organisms and river environments, with important implications for managing river habitat. 

The hydrodynamic signature of biologically-generated flows
Of particular importance is how sensory information may be masked by the ambient environment. For example, many animals in rivers are thought to be able to sense the presence of other organisms from their hydrodynamic wake. However, this raises the question: How can an animal differentiate the turbulence generated downstream of an animal from the turbulence of the ambient environment? To investigate this, I quantified the turbulent flow downstream from living crayfish, inanimate crayfish replicas and over plane beds. Living crayfish could be differentiated from other objects under some ambient conditions, but when the substrate was coarse and the velocity was fast, this ‘crayfish signal’ was masked by the ambient hydraulics. Consequently, the ability of animals to utilise hydrodynamic (and other) senses is likely to be dependent on the environmental context
A PIT-tagged signal crayfish
 A signal crayfish with a PIT tag attached to its cephalothorax (back)

Flow visualisation over a living, moving crayfish
Visualisation of the flow over a living crayfish

Particle Image Velocimetry (PIV) to quantify the turbulent flow over moving crayfish