Early-life temperature drives recruitment success in Eurasian perch (Perca fluviatilis) populations

Interannual fluctuations in the abundance of young-of-the-year (YOY) European perch (Perca fluviatilis) were studied in two large French peri-alpine lakes using a 12-year dataset of late summer hydroacoustic surveys. Previous research based on sampling over only a few years in localized areas or experimental systems has already highlighted the importance of temperature. However, these studies often considered only monthly or seasonal averages. In our study, we sought to understand the factors behind the significant annual fluctuations in perch stock and analysed 12 years of data at the ecosystem level. We used traditional thermal indices based on average values, as well as novel indices reflecting daily temperature fluctuations, which were derived from 36 years of in situ perch spawning data. Embryonic thermal conditions alone accounted for between 44% and 88% of the variation in YOY density across the lakes. An increase in temperature during the embryonic phase was beneficial, whereas significant daily variations had the opposite effect. In contrast, trophic factors and the adult stock did not exhibit consistent trends. Our study confirms previous findings using ecosystem-scale analyses, long-term data, and novel thermal indices, validating in natura the central role of spring thermal regimes in shaping recruitment and improving our understanding of recruitment variability under climate change.