Habitat Use of Pre-Spawning Adult Pacific Lamprey At Three Spatial Scales in North Umpqua River, Western Oregon, USA

We describe the holding and overwintering habitat use of pre-spawning adult Pacific lamprey at the macro, meso, and micro spatial scales.  To date, little research has focused on the habitat use of pre-spawning adult Pacific lamprey.  During 2009-2010, a total of 70 fish were radio tagged between May and September and were released in the lower North Umpqua River (~3,500 km² watershed).  At the macro scale, as represented by 1 km reaches, the radio tagged lamprey were concentrated in reaches that had high levels of sinuosity and many short segments of riffle habitats.  At the meso scale, as represented by individual habitat units (pool/riffle/run/glide), run and riffle habitats were used significantly more in comparison to available habitat.  At the micro scale, as represented by the precise positions within the habitat units, the interface of habitats (head and tail regions) were used significantly more for riffle and run habitats, while there was no distinct pattern observed for pool and glide habitats.  Finally, using the results from the combination of radio tracking, digital elevation models, and thermal infrared surveys, we hypothesize that hyporheic exchange flow may be a potential driver for the holding and overwintering habitat of these lamprey.