Rotary screw traps were used to estimate Pacific lamprey smolt yield,
outmigration timing, age structure and sex ratio for Tenmile Creek basin, Lane County,
Oregon. Traps were fished March to June and August to December 1994 and March to
June and October to December 1995. Lamprey smolts caught in the traps were marked
and released upstream. Recaptured fish were used to calculate trap efficiencies and daily
and weekly estimates of outmigrating smolts. Little movement of smolts occurred before
November. Outmigration peaked in late November and was complete both years by 2
December. Ages of smolts were determined using length-frequency analysis and by
reading statoliths. Tenmile Creek Pacific lamprey smolts have an extended freshwater
residency. Male to female ratios were approximately 1:1 both years. Larval, metamorphosing and smolting Pacific lamprey were examined for changes
in skin guanine concentrations, gill (Na+K)-ATPase activities and plasma thyroid
hormone levels during a 14 mo period. Seasonal peaks were observed in gill (Na+K)-ATPase activities and plasma thyroid hormone levels in larvae. Metamorphosing and
smolting lamprey showed increases in skin guanine concentrations and gill (Na+K)-ATPase activities along with decreases in plasma thyroid hormone levels. Smolting
lamprey challenged with artificial seawater showed no significant changes in the
parameters observed
