Growth Dynamics of Coastal Cutthroat Trout in Headwater Streams

Growth can be a critical factor affecting the behavior of stream fishes.  Although factors that influence growth have been well studied in laboratory settings, the complex interactions among environmental variables and life history strategies are still poorly understood for many species of stream dwelling fishes.  Age 1+ individuals implanted with Passive integrated transponders (PIT tags) were monitored across space and time.  Growth data from multiple watersheds over a 12-year period were summarized to elucidate patterns of growth for individuals and populations of headwater coastal cutthroat trout Oncorhynchus clarkii clarkii.  It appears that factors influencing growth fluctuate in both space and time.  For example, annual relative growth rates for age 1+ coastal cutthroat varied among watersheds and among stream segments within watersheds in most years.  However, annual relative growth rates generally exhibited substantial synchrony among watersheds.  Furthermore, disturbances such as clearcut logging and a dam-break flood resulted in changes in annual growth rate relative to reference sites as the forest canopy was opened and growing season was extended.  Individual cutthroat trout recaptured over multiple years displayed diverse patterns of growth ranging from none to constant rates over multiple years.  Within an individual year, seasonal growth rates were greatest in the late fall and spring.  Results suggest that local variation in growth may be influenced by both variation in habitat conditions and genetic variation, and riverscape-scale patterns reflect broad climatic and physiochemical conditions.