It is rare to have longitudinal data on the somatic growth of fish, that is, how their body length changes over time. In most temperate fish, scales or other hard parts, like otoliths or other bones, form annual rings or increments. Growth of the hard part can be measured, thereby giving a longitudinal record of hard part growth from cross-sectional data. Methods such as back-calculation and linear mixed-effects models have used the growth of hard parts to infer somatic growth.
At times, it is not feasible to obtain the measurements of the hard part. Body length at time of capture is much easier to measure and reflects somatic growth, which is usually of more interest. In this thesis, I present a model that is based on a longitudinal approach but models length at time of capture, rather than the yearly body growth. It also allows for estimation of environmental impact on growth.