Age-growth, mortality, and models predicting growth of redband trout in high desert streams of Idaho

Large gaps in population dynamics information exist for redband trout residing in arid environments.   We estimate natural mortality in nine Idaho streams, estimate longevity and growth in each population, and investigate relationships between growth and  abiotic habitat parameters via multiple regression.  The longevity of redband trout collected from the study streams ranged from 2 to 9 years.  Natural mortality approximations ranged from 0.41 in Little Jacks Creek to 0.88 in Sinker Creek.  Males grew faster than females and attained greater maximum length in eight of nine streams.  The reason for the consistent smaller size of females is unclear but could be the result of a conflict in the timing of somatic and gonadal growth.   The best models relating first year growth of redband trout to abiotic variables included mean fall-spring temperature and elevation for both sexes and explained 52% and 59% of the variation in length at age 1 for males and females, respectively.  The fall-spring period (September to May) is a more important  period for redband trout growth in desert streams than the summer period (June to August).   This unexpected observation, apparently related to  excessive mid-summer water temperatures,  has been reported by a previous author as inverted seasonal growth.