Summertime movement, biomass, and abundance of co-dominant cutthroat trout and Pacific giant salamanders in Cascade Mountain headwater streams

Identifying the patterns and drivers of movement is critical for understanding species
biology, population dynamics, and community ecology. Movement of co-dominant fish and
salamander species has never been studied concurrently in lotic environments despite their
importance as vertebrate predators. We conducted a mark-recapture survey of cutthroat trout
(Oncoryhnchus clarkii) and Pacific giant salamanders (Dicamptodon tenebrosus) in two
reaches of a 3rd order headwater stream to determine movement patterns during summer. We
also conducted biomass and abundance surveys at four sites along the 2km stream to learn
how the species composition of these two co-dominant vertebrates changes along a stream
gradient. We found that D. tenebrosus show a distinct upstream movement bias while O.
clarkii are generally immobile during summer low flow. We also found that length is
significantly correlated to movement for D. tenebrosus. Additionally, along a stream
gradient, biomass/m2 is relatively constant and similar for both D. tenebrosus and O. clarkii.
Keywords: Dicamptodon tenebrosus, Oncoryhnchus clarkii, cutthroat trout, Pacific giant salamander, movement, season