Partial Migration in Salmonids: Environmental Controls and Resilience

Partial migration, in which populations exhibit both migratory and non-migratory behavior, is common among several species of salmonids.  Migratory polymorphism is diverse and can range from relatively short migrations between streams and lakes to long-distance migrations between rivers and the open ocean.  For salmonids occupying unstable or unpredictable environments, partial migration can act as a buffer against extinction by distributing risk across environments. While the genetic and ecological relationships between and among life history types remains an unanswered question in many cases, how we treat sympatric life history types has significant implications to management and research.  In this presentation, I will examine how environment influences migratory polymorphism using brief case studies of Sakhalin taimen (Parahucho perryi) and rainbow trout (Oncorhynchus mykiss).  While management of polymorphic species can clearly impact life history variation at the local scale, I propose that management of other species and habitats can have similarly strong influences, which may result in reduced resilience.