Table 1 Parameters included in the step selection functions. Spatially varying parameters are environmental parameters that are not uniform across the study site at a point in time. Movement parameters are parameters describing elements of the fish’s movement or position. Other environmental parameters are external parameters that are uniform across the study site (e.g. temperature does not change between true and null steps in the step selection function): these parameters were only included via interactions

Spatially varying parameters, available at the start and end of steps

Flow velocity

WV

Flow velocity, in meters per second

Spatial velocity gradient (SVG)

SVG

The spatial change of flow velocity between cells in the hydraulic model, in meters per second per meter

Water depth

D

Depth of water, in meters

Difference between flow angle and fish’s angle

DiffVang

The angular difference between the direction of the flow velocity and the direction of the fish (where 0° is north). Modelled as the cosine

Difference between SVG angle and fish’s angle

DiffSVGang

The angular difference between the direction of the SVG and the direction of the fish (where 0° is north). Modelled as the cosine

Movement parameters

Step length

SL

Distance travelled in a step, modelled as its logarithm

Turning angle

TA

Angle at which a fish has turned from the preceding step, modelled as the cosine

Other parameters

Temperature

Temp

Recorded by each receiver every 15 min. Median value taken for the whole study site. Temperature record closest in time to a fish position was used.

Time of day

TOD

Points categorised as dawn, day, dusk or night, based on nautical twilight.