Evaluation of Bull and Brown Trout Responses to Increased Habitat Complexity

One of the greatest threats facing indigenous salmonids of the Pacific Northwest is the introduction of and competition with nonnative species.  For instance, brook trout Salvelinus fontinalis have been introduced outside their native range and are known to hybridize with and displace bull trout Salvelinus confluentus, a federally threatened species.  The effects of brown trout Salmo trutta on bull trout, however, are not well understood and much remains to be learned.  Research suggests that bull trout fare better in competitive interactions with nonnative trout if habitat complexity, such as large woody debris, is high.  A reduction in complex habitats is detrimental for native salmonids and may enable nonnative species to colonize degraded habitat.  Therefore, resource managers need to understand if enhancing habitat complexity in degraded reaches of streams facilitates recovery of bull trout in the presence of nonnative trout.  In 2010, we began a manipulative experiment to assess whether enhancing habitat complexity in streams within the upper Klamath River basin will benefit bull trout where they are sympatric with nonnative brown trout.  The experiment is being conducted in small, high elevation streams that have a history of extractive forestry operations.  We are using capture-recapture methods with passive integrated transponder tags to quantify changes in growth, condition, movement, and survival of both species before and after experimental treatments involving the addition of large woody debris to selected stream reaches.  Additional reaches similar to the treatment reaches are being monitored as controls, and changes in the physical habitat in both the treatment and control reaches are also being monitored.  The experiment is in the beginning stages with pre-treatment habitat monitoring concluding in 2011, treatment occurring in 2012, and post treatment monitoring occurring until 2014.  Fish tagging will continue throughout the duration of the project.