Life at the top: Coastal cutthroat trout in headwater streams

Headwater streams are complex networks that form a physicochemical template governing the persistence of aquatic species such as coastal cutthroat trout Oncorhynchus clarkii clarkii.  To gain insight into these interactions, we have been studying the distribution and abundance of this native trout in headwater streams (500-1000 ha) of western Oregon for the past 12 years.  Evidence suggests that movement is common at the channel-unit scale throughout the year, but reach- and segment-scale movements are frequent during the winter and spring.  Barriers to movement can influence phenotypic and genetic attributes of isolated populations, and isolation may compromise persistence.  Low-discharge periods appear to be annual survival bottlenecks, and interannual survival is related to precipitation patterns.  Within individual stream networks, food availability differs among vegetation types, but relative growth rates were similar among streams.  In fact, differences in size structure among populations appear to be more strongly linked to survival than growth rate.  Recent growth estimates from individuals that were implanted with passive integrated transponders and subsequently recaptured in successive years imply that growth is highly variable within and among streams and years.  Fish-habitat relationships in these relatively simple stream networks underscore the complexity of these systems and the limits of current understanding.