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, and Modified Fry) used to back-calculate 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.