Early Male Maturation of Chinook Salmon Caught at Sea

Variation in age and size of maturity of male Chinook salmon has been apparent at freshwater spawning sites from the earliest studies of these fish.  Study of fish rearing in the ocean is more difficult and an appreciation of the variety of male maturation strategies is less apparent.  Sampling of fish may occur at seasonal times when maturation status is not easily visible and consequently maturation status may not be easily quantified.  A sampling program for juvenile salmon in the Northern California Current has occurred over the past 10 years.  In this study the maturation status of the Chinook salmon captured has been directly assessed by measuring plasma androgen levels.  Maturing age 2 (miniJack) Chinook salmon are commonly captured.  The occurrence and distribution of this life history variant at sea has not been previously described.  In addition, growth status of the animals captured is assessed by measuring plasma levels of the hormone insulin-like growth factor 1.  We will assess how varying growth levels between years relates to the proportion of spring Chinook salmon that mature as jacks (age 3) in the following year.