Larger but younger fish when growth outpaces mortality in heated ecosystem

Area of Science:

• Ecology
• Climate Change Biology
• Fisheries Science

Background:

• Global warming is predicted to decrease ectotherm body size based on growth models and the temperature-size rule (TSR).
• Warming's impact on population size structure depends on its effects on mortality, juvenile growth, and adult growth rates.
• Eurasian perch (Perca fluviatilis) are ectotherms whose population dynamics may be sensitive to warming.

Purpose of the Study:

• To investigate the long-term effects of sustained warming (5-10 °C above ambient) on the growth, size-at-age, mortality, and population structure of Eurasian perch.
• To determine how warming influences body size and age distribution in a wild fish population.

Main Methods:

• Utilized a unique, two-decade-long dataset from an artificially heated bay and a reference area.
• Employed growth-increment biochronologies to reconstruct length-at-age for 2426 Eurasian perch individuals (12,658 estimates).
• Quantified mortality rates and population size- and age structure using catch data.

Main Results:

• Perch in the heated area exhibited faster growth rates across all sizes, resulting in larger size-at-age for all ages compared to the reference area.
• Despite higher mortality rates (reducing mean age by 0.4 years), faster growth led to a 2 cm increase in mean body size in the heated area.
• Statistical analysis of the size-spectrum exponent, which describes abundance decline with size, yielded less clear results.

Conclusions:

• Warming significantly increases Eurasian perch growth rates and mean body size, even with elevated mortality.
• Mortality rates, alongside plastic growth and size responses, are critical factors influencing population size structure under warming conditions.
• Understanding these mechanisms is vital for predicting climate change impacts on ecological functions and population dynamics.