Quantitative Assessment of the Limiting Factors Affecting Salmonid Populations

Native salmonids have declined throughout their range in response to habitat loss and fragmentation in combination with other factors. Quantification of the links between habitat needs and demographic parameters are necessary to prevent further loss of these species and guide restoration efforts. However, in order to direct recovery efforts, we need research techniques that can account for multiple life-history strategies, accurately assess populations across landscapes, and understand the specific age/stage class that is potentially limiting population growth rates. To address these concerns, we are conducting a multiple system, mark/recapture project in conjunction with habitat surveys to understand the limiting factors affecting bull trout populations in northeastern Oregon. Our sampling design in combination with current technology allow for effective sampling across different life-history strategies and across spatial differences within each watershed, and ultimately will allow for direct comparisons of potential bottlenecks between populations. Our results suggest that the current monitoring techniques may not be appropriate for effectively monitoring the population trends of different bull trout life-history forms. Furthermore, these results indicate that monitoring techniques of declining salmonid populations need to be validated with respect to current management objectives