Seasonal Survival and Emigration of Juvenile and Adult Brown Trout in Streams of Southeast Minnesota

We assessed the influence of reach characteristics and seasonal patterns on estimates of survival and emigration of brown trout in six interconnected stream reaches in southeast Minnesota.  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) from September 2006 through October 2008.  Survival of the 2006 age 0 cohort varied by season, being highest in winter (0.73, 95% CI=0.56-0.85) and lowest during spring (0.59, 0.42-0.74), but did not differ among reaches.  Emigration of age 0 trout also varied by season but not reach, being 0.03 (0.01-0.06) in fall, 0.06 (0.03-0.14) in winter, and 0.10 (0.06-0.15) in spring.  Survival of age 1 and 2 trout differed among seasons being consistently highest in winter and lowest in fall.  Age 1 and 2 emigration was influenced by reach characteristics but not by season.  Overall emigration rates ranged across reaches from 0.01 to 0.26 per season.  Reach influenced both survival and emigration of age 3+ trout.  Very few or no age 3+ trout were captured in the three shallowest reaches with the least cover.  Survival ranged among remaining reaches from 0.77 (0.70-0.83) to 0.89 (0.85-0.92) and emigration from 0.02 (0.01-0.04) to 0.05 (0.02-0.16).  Survival was highest and emigration lowest in reaches with the most cover, including deep pools.  These data illustrate the complex interactions among reach-scale habitat characteristics, seasonal patterns, and fish age and size influencing brown trout survival and emigration.