# Reconstructing History: Scale Analysis Reveals Long‐Term Changes in Age‐Related Growth of a Coregonid Fish

## TL;DR

This study uses fish scales to track changes in growth over 22 years, showing how environmental factors and life stages affect growth patterns in a lake fish population.

## Contribution

The study provides rare empirical evidence of age-specific growth changes linked to environmental factors and life-history strategies in a natural fish population.

## Key findings

- Growth in younger fish remained stable or increased slightly, while mature fish showed declining growth over time.
- Phosphorus concentrations decreased, but spring temperatures showed no long-term trend.
- Temperature effects on growth varied by age class, suggesting age-specific interactions with environmental changes.

## Abstract

Animal growth is shaped by a complex interplay of environmental conditions and intrinsic life‐history trade‐offs, yet long‐term datasets allowing the reconstruction of individual growth histories in natural populations remain rare. Here, we use scale analysis to reconstruct age‐specific growth histories of coregonid fish (Coregonus sp.) from Lake Starnberg, Germany, over a 22‐year period, evaluating the roles of lake phosphorus concentrations and spring temperatures as potential drivers. Linear mixed‐effects models revealed age‐specific changes in scale growth over time: while growth remained stable or increased slightly in younger age classes (ages 1 and 2), growth significantly declined over time in mature fish (age 3). During the observed period, phosphorus concentrations decreased, indicating reduced nutrient availability, whereas spring temperatures showed no significant long‐term trend. Our analyses further indicated significant interactions between temperature and age class, suggesting that temperature effects on growth may have varied by age, even though there was no overall change in temperature during the monitored time period. The observed decline in growth among mature individuals aligns with predictions from life‐history theory, reflecting a potential allocation shift from somatic growth to reproductive investment following maturation. This study provides rare empirical evidence from a natural fish population that long‐term environmental changes interact with intrinsic life‐history strategies, resulting in clear age‐specific patterns of growth variation.

Model fit for change in scale radius length over time by age class, based on linear mixed effect models for (i) radius length as a function of year, age class, and subsequent interaction (dashed lines), and (ii) radius length as a function of year, temperature, phosphorus, and age class, as well as interactions between temperature and phosphorus with age class.