Why Are There so Many Sneaky Males? Changes in the Proportion of Precocious Males over 16 Years in Columbia River Chinook Salmon Populations

The precocious male phenotype has been documented as a successful strategy for male salmonids, though it has historically been maintained at low proportions within populations.  Precocious males reach sexual maturity at age 1 or 2, but do not generally express secondary sexual characteristics (e.g., large body size, enlarged jaws).  Anthropogenic changes throughout the Columbia River Basin have altered many of the natural environmental regimes and historic patterns observed in biotic communities.  Increases in the precocious male strategy within salmonid populations could intensify competition for limited freshwater resources and reduce the amount of marine-derived nutrients entering freshwater and terrestrial systems.  This research utilized ~16 years of adult return data from PIT-tagged fish passing the Bonneville Dam on the Lower Columbia. Annual changes and trends in occurrence of the precocious male life history strategy of Chinook salmon (Oncorhynchus tshawytscha) were compared.  Early results suggest that the proportion of precocious males has substantially increased over the past 16 years (1997 – 2013).  Future research will focus on environmental and anthropogenic drivers as potential mechanisms of changing strategies. Shifts in life history strategies could have large impacts on management strategies and options for the conservation and recovery of salmonid species within the Columbia Basin.