The anadromous Pacific Lamprey Entosphenus tridentatus is native to the northern Pacific Ocean and its drainages, returning each spring to spawn in streams along the West Coast of North America. We analyzed abundance trends of adult Pacific Lamprey from dam counts and redd surveys in western Oregon, USA. We compared a series of generalized additive models (GAMs) to describe lamprey abundance trends. Lamprey counts varied considerably among dams but showed steep declines over 70+ years at Bonneville Dam on the Columbia River, over 50+ years (1965-2019) at Winchester Dam on the North Umpqua River, and over 17 years (1993-2009) at Gold Ray Dam on the Rogue River. By contrast, redd surveys displayed synchronous abundance trends of different magnitudes among geographic management areas on the Oregon coast, with an overall increasing abundance over 13 years (2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019). This corroborates pre-existing notions that Pacific Lamprey spawning in Oregon coast rivers are from a single mixed population. The most supported GAM included a fixed effect for location and allowed abundance to vary over years as a function of location. These results suggest that abundance trends among dam counts are more variable than coastal redd surveys and that dam counts and redd surveys across this large region are not useful proxies for each other. Furthermore, counts across dams may be more variable because they record prespawning lamprey and thus may be recording a mixture of cohorts. Redd surveys, by contrast, provide a metric of a single cohort of spawning lamprey.

Intra‐ and interspecific competition for spawning space is a commonly observed interaction in salmonids that can result in progeny loss. This study examined the impacts of redd superimposition by kokanee Oncorhynchus nerka on the reproductive success of bull trout Salvelinus confluentus in the Deschutes River basin, Oregon. The activities of high‐density spawning groups of kokanee were hypothesized to place the eggs and alevins of bull trout at risk of displacement and damage wherever the spawning habitats of these two species overlap. Bull trout egg pocket depths and kokanee scouring depths were measured. Fry emergence from redds, a proxy for bull trout reproductive success in the presence of kokanee, was compared between superimposed and undisturbed redds by using fry emergence traps. Our results indicate that groups of spawning kokanee did not scour the stream bed deeply enough to reach bull trout eggs. Data on bull trout fry emergence revealed that kokanee redd superimposition did not affect bull trout egg‐to‐fry survival rates.