Modelling fishing-induced evolution in pikeperch (Sander lucioperca) and vendace (Coregonus albula), Lake Oulujärvi, as template for ecosystem model.

Abstract

Fishing-induced evolution can impact fish trait distributions, with previous studies highlighting declines in size and age at maturation. However, the effects on fish growth remain less understood, and different fishing methods may exert distinct selection pressures on populations. This study explores the impact of gillnetting on pikeperch (Sander lucioperca, Percidae) and trawling on vendace (Coregonus albula, Coregonidae) modelled using data-based normally distributed selection curves and the Allometric Trophic Network with Evolution model (Perälä & Kuparinen). Simulating evolutionary changes caused by fishing, we specifically examined the parameters of the von Bertalanffy model, including asymptotic length $\left(L^{\infty }\right)$ and Brody's growth coefficient $\left(k\right)$ . In the model we simulated a negative correlation (-0.7) between asymptotic length and Brody's growth coefficient. We investigated the effects of parameters related to genotypic and phenotypic variance and the amount of correlation between asymptotic length and Brody's growth coefficient in the model using sensitivity tests. Trawling induces evolution in C. albula towards smaller asymptotic length, whereas Brody's growth coefficient stays at intermediate levels. The results for C. albula were consistent across different levels of correlation. Gillnetting of S. lucioperca results in evolution in asymptotic length and Brody's growth coefficient in variable directions. Frequently, S. lucioperca evolved towards larger size and growth, but depending on parametrization, selection can also be disruptive, or S. lucioperca may evolve towards smaller size and growth. The amount of genotypic and phenotypic variance also influences these outcomes, whereas instantaneous fishing mortality impacts biomasses across the food web. This study underscores the significance of considering fishing-induced evolution, its impact on fish growth and food web-level effects, in addition to the densities of targeted species. Such insights are crucial for a comprehensive understanding of the ecological consequences of fishing practices.