State-dependent life history plasticity in Sacramento River winter-run chinook salmon (<i>Oncorhynchus tshawytscha</i>): interactions among photoperiod and growth modulate smolting and early male maturation

Abstract

An experiment was performed to determine the relative effects of photoperiod at emergence and growth rate on smolting pattern and early male maturation rate in Sacramento River (California, USA) winter-run chinook salmon (Oncorhynchus tshawytscha) (listed as endangered under the US Endangered Species Act). Fry were ponded on the same day but at three different points in the seasonal photoperiod cycle (using artificial lighting) spanning the natural range of emergence timing in this population. Significant increases in gill Na + ,K + -ATPase activity and seawater survival were found during March and April in all treatments, similar to yearling smolting patterns found in many salmonids. Fish that emerged early and grew at a relatively high rate also demonstrated signs of smolting in August–November. Male maturation was growth dependent, with HiFeed groups maturing at a rate double that found in LoFeed groups. Male maturation was also photoperiod dependent with a linear relation found between emergence date and rate of male maturation. These results demonstrate that individual life history pattern was variable and dependent on emergence timing and growth rate.