Larval Fish Transport and Retention and the Importance of Location for Juvenile Fish Recruitment in Upper Klamath Lake, Oregon

In the Upper Klamath Lake basin of Oregon, we applied the member-vagrant hypothesis to larval lake fishes, documented marsh and hydrographic retention for larval shortnose suckers Chasmistes brevirostris and Lost River suckers Deltistes luxatus, and examined the effect of larval retention on the shoreline abundance of the juveniles of five species of fish in August. Emigration of larval suckers was highest from natal rivers, and immigration was highest in nonnatal areas downstream of the lake. Lake retention was facilitated by a wind-generated gyre and advection by an eastern boundary current. Marshes and other shoreline irregularities acted as traps that slowed river and eastern boundary current advection and retained larvae, especially for shortnose suckers, for up to 3 weeks. The interaction of behavior, seasonal spawning, and seasonal system dynamics appears to drive retention patterns. For both species of suckers and three minnow species (fathead minnow Pimephales promelas. blue chub Gila coerulea, and tui chub G. bicolor), the abundance of juveniles along the shoreline increased with distance from the lake outlet and was weakly related to lake elevation, a surrogate for available habitat. For these five species, 45.5% of the variation in August juvenile abundance was determined by distance from the lake outlet. This work suggests that the nonbehavioral component of freshwater retention is complex and depends on hydrographic features, the boundary conditions of hydrographic features. and shoreline habitat.