Biomass and sustainable yields of Eurasian perch (Perca fluviatilis) in small boreal lakes with respect to lake properties and water quality

Understanding of factors that explain variation in potential fisheries yields is essential for the ecosystem-based management of lake fisheries. We used mark-recapture and Nordic survey net sampling to obtain estimates of Eurasian perch (Perca fluviatilis) abundance in 28 small (13.3 ha ± 11.4 ha, mean ± S.D.) boreal lakes. A size-structured population model was calibrated for each lake using further individual data to derive estimates of potential yields. Principal component scores formed from physical and chemical environmental parameters and a simple score reflecting the relative photic area of the lakes were then used to explain variation in theoretical yields to identify potential environmental proxies for fisheries management purposes. The estimated mean biomass of perch in the study lakes was 52.4 ± 51.2 kg ha⁻¹, and the maximum sustainable yield, obtained with environment-dependent recruitment size was estimated to be 9.4 ± 12.1 kg ha⁻¹ yr⁻¹. The estimated yields were highest in shallow lakes with good oxygen saturation and with high percentage of euphotic bottom while excess nutrients decreased yields and alkalinity was marginally predictive for catch of large individuals. Our study provides quantitative estimates of potential yields of varyingly sized perch and helps to develop environmentally informed management for small lakes of which some are surprisingly productive.