TY - JOUR TI - Larger but younger fish when growth outpaces mortality in heated ecosystem AU - Lindmark, Max AU - Karlsson, Malin AU - Gårdmark, Anna A2 - Donoso, David A A2 - Schuman, Meredith C A2 - Stawitz, Christine VL - 12 PY - 2023 DA - 2023/05/09 SP - e82996 C1 - eLife 2023;12:e82996 DO - 10.7554/eLife.82996 UR - https://doi.org/10.7554/eLife.82996 AB - Ectotherms are predicted to ‘shrink’ with global warming, in line with general growth models and the temperature-size rule (TSR), both predicting smaller adult sizes with warming. However, they also predict faster juvenile growth rates and thus larger size-at-age of young organisms. Hence, the result of warming on the size-structure of a population depends on the interplay between how mortality rate, juvenile- and adult growth rates are affected by warming. Here, we use two-decade long time series of biological samples from a unique enclosed bay heated by cooling water from a nearby nuclear power plant to become 5–10 °C warmer than its reference area. We used growth-increment biochronologies (12,658 reconstructed length-at-age estimates from 2426 individuals) to quantify how >20 years of warming has affected body growth, size-at-age, and catch to quantify mortality rates and population size- and age structure of Eurasian perch (Perca fluviatilis). In the heated area, growth rates were faster for all sizes, and hence size-at-age was larger for all ages, compared to the reference area. While mortality rates were also higher (lowering mean age by 0.4 years), the faster growth rates lead to a 2 cm larger mean size in the heated area. Differences in the size-spectrum exponent (describing how the abundance declines with size) were less clear statistically. Our analyses reveal that mortality, in addition to plastic growth and size-responses, is a key factor determining the size structure of populations exposed to warming. Understanding the mechanisms by which warming affects the size- and the age structure of populations is critical for predicting the impacts of climate change on ecological functions, interactions, and dynamics. KW - Perca fluviatilis KW - body growth KW - size KW - size-spectrum KW - mortality KW - climate change JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -