Reconstructing salmon growth trajectories through biochronologies across a highly variable growthscape

Measuring the growth of migratory fish across habitats is difficult because field observations only provide a snapshot into their life; yet, understanding which habitats provide better growth opportunities is crucial for their conservation. We experimentally enclosed individually tagged juvenile Chinook Salmon (Oncorhynchus tshawytscha) in habitats with known differences in growth potentials to evaluate four different models (Dahl-Lea, Fraser-Lee, Biological Intercept, Modified Fry) used to back-calculated size-at-age from otoliths. We found that otolith-derived fish size reconstructions were most accurate using the Biological Intercept or Modified Fry model, though bias remains for slow growing fish. This tool was then used in a case study to reconstruct the mosaic of inter- and intra-habitat growth opportunities available to fishes, providing a useful framework for assessing and monitoring fish responses to habitat restoration and a changing environment.