A Discussion of Otolith Chemistry Methodology Used to Estimate Life-History Parameters in Three Salmonid Species

Life history parameters derived from otolith (ear bone) chemistry have become increasingly used in the research and management of anadromous salmonids. Otoliths are mineralized structures that grow throughout the life of a fish and incorporate elements such as strontium in proportion to its abundance in the environment. In many systems water strontium:calcium (Sr:Ca) is lower in fresh versus brackish/marine water  and otolith chemistry may provide estimates of marine migration size, timing, and maternal origin. Here we present three analyses in which naturally occurring variation in Sr:Ca are employed to answer questions relating to life history strategies of anadromous salmonids. First we analyze otolith cores of juvenile Oncorhynchus mykiss to determine maternal origin (anadromous versus resident). Second we quantify daily growth increments and otolith Sr:Ca to estimate estuarine and marine habitat use by juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon. Lastly we measure otolith Sr:Ca and use back-calculation models to calculate size at marine entry to assess survival of different juvenile life history strategies.