Increased temperatures favour reproductive investment in smaller over larger female common sole (Solea solea) in the Northeast Atlantic

Reproductive investment is a major life history trait affecting individual fitness. Understanding reproductive investment is important to assess population dynamics under current and future environmental changes. A major environmental change that affec t s the r epr oduc tive investment of fish populations is local warming under on-going climate change. In this study, we investigated the effec t s of increased temperature on the reproductive investment of female fish across different body sizes (measured as total length). To this end, we applied a mixed-effec t s modelling framework to a large dataset of 4637 observa- tions of ovary weight from developing-stage female individuals collected from 2004 to 2022 from four populations of common sole ( Solea solea ): the North Sea, Irish Sea, Bristol Channel-Celtic Sea North, and Eastern English Channel populations. We found that increased temperature had different effects on fish reproductive investment across body sizes, i.e. enhanced re- productive investment in smaller individuals, but reduced investment in larger individuals in the North Sea and Irish Sea sole populations. No significant size-specific temperature effect was detected in the Bristol Channel-Celtic Sea North and Eastern English Channel populations. In addition, we found that the reproductive investment of sole exhibits hyper-allometric scaling (positive allometry) with body size. Our study sheds light on how temperature changes influence fish reproductive investment, with implications for population dynamics.