Relative Importance of Recruitment, Survival, and Immigration of Three Age Groups of Brown Trout in Southeast Minnesota Streams

We estimated how much recruits, survivors, and immigrants contributed to population size in six reaches in southeast Minnesota.  Recruitment was determined from population estimates made in September.  Survival and emigration were estimated from mark and recapture of individually PIT-tagged brown trout, representing three ontogenetic groups (age 0, age 1 and 2 adults, age 3+ large adults) across reaches and four seasons (see associated Poster).  Immigration was calculated as one minus emigration.  Recruitment varied among the six reaches and three years of this study (range 0-1,292/km) and was consistently low in all reaches in 2007 due to flooding.  Survival and emigration varied by reach or season depending on ontogenetic group (see associated poster).  For age 0 trout, immigrants were estimated to contribute 50% or more of age-0 abundance in three of the six study reaches.  In the other three reaches, immigrants contributed 0% to 35%.  Recruitment (i.e., aging of age 0 trout to age 1) was estimated to contribute more than 50% of age 1 and 2 trout to most reaches, especially in 2006-2007 as a result of a large 2006 year class.  Survival was estimated to account for 50% or more of the predicted abundance of age 3+ trout in almost all reaches.  Although variable, broad patterns suggest that age-0 populations are dependent on immigration, age 1 and 2 adults on recruitment, and age 3+ trout on survival.