Model-based evaluation of the management of pikeperch (Sander lucioperca) stocks using minimum and maximum size limits

Pikeperch populations typically differ substantially in life-history traits. Here, we evaluated the potential of variable size limits to ensure ecologically and evolutionarily sustainable fishing of six important Finnish inland pikeperch stocks using a carefully parameterized age-, size-, and maturity-structured evolutionary population model. Individual growth rates of the Oulujärvi and Vesijärvi stocks were the fastest and least resource-limited. The Höytiäinen, Vanajavesi and Pääjärvi stocks were strongly regulated by density-dependent food availability. Minimum size limit ensuring the highest yields was clearly higher for the fast-growing stocks than for the strongly food-limited stocks. Implementation of a maximum size limit 200 mm above the minimum size limit (MSL) would allow the stocks to tolerate stronger fishing mortality rate, but the 200 mm slot appeared too wide to significantly prevent evolution towards earlier maturation. To ensure maximal stability of yield and minimal evolutionary effect, fishing mortality rates should be restricted to relatively low values.