Life-history diversity and its importance to population stability and persistence of a migratory fish: steelhead in two large North American watersheds

1. Life-history strategies can buffer individuals and populations from environmental variability. For instance, it is possible that asynchronous dynamics among different life-histories can stabilize populations through portfolio effects. 2. Here we examine life-history diversity and its importance to stability for an iconic migratory fish species. In particular, we examined steelhead (Oncorhynchus mykiss), an anadromous and iteroparous salmonid, in two large, relatively pristine, watersheds, the Skeena and Nass, in northwestern British Columbia, Canada. We synthesized life-history information derived from scales collected from adult steelhead (N = 7227) in these watersheds across a decade. 3. These migratory fishes expressed 36 different manifestations of the anadromous life-history strategy, with 16 different combinations of freshwater and marine ages, 7.6% of fish performing multiple spawning migrations, and up to 4 spawning migrations. Furthermore, in the Nass watershed, different l...