Iteroparity in Atlantic Salmon and Steelhead Trout: a Contrast and Comparison

Among the Pacific salmonids (Onchorynchus spp), steelhead are unique because they are potentially iteroparous.  Indeed, for many years they were placed in the same genus with Atlantic salmon and brown trout (Salmo spp). I will compare and contrast what is known about iteroparity in steelhead with what is known about iteroparity in Atlantic salmon.  i will then explain a life history theory that combines proximate (physiological) and ultimate (evolutuionary) mechanisms, and which has been applied to both Atlantic salmon and steelhead.  This theory allows us to place the empirical comparisons in a conceptual framework.