Distribution and Apparent Movement of Age-1 Lost River and Shortnose Sucker in Upper Klamath Lake, Oregon, in Response to Poor Water Quality

The influence of poor water quality on the distribution, movement, and survival of age-1 Lost River sucker (Deltistes luxatus), and shortnose sucker (Chasmistes brevirostris) within Upper Klamath Lake, Oregon, is not well understood. Our goal was to assess seasonal changes in the distribution and abundance of age-1 Lost River and shortnose suckers as they relate to dissolved oxygen (DO) concentrations and habitat characteristics. We collected juvenile suckers between April and September 2007-2009 and recorded a variety of habitat parameters at each sampling site. We examined water quality from 2007 to 2009 at a minimum of 16 monitoring stations that encompass the range of conditions present within Upper Klamath Lake. Mean daily DO concentrations were below 4 mg/L each year in July, August, and September with the most frequent declines and lowest DO levels occurring along the lake’s western shore and open water areas in the north. Spatial-temporal patterns in catch rates of age-1 suckers suggest initial movement toward deep water areas and shallow bays along the western shore in late June and early July followed by movement away from these areas as DO concentrations dropped below 4 mg/L. It is unclear from our results why age-1 suckers move toward the western shore in late spring, but poor water quality events provide a likely explanation for their exit from these areas in mid-summer. A distributional shift of age-1 suckers after mid-summer declines in water quality, followed by their near-disappearance in late-summer, suggests poor water quality may also affect overall survival.