Preface to the Special Issue “Ecologically sustainable fishing”: Project KESKALA background, objectives and conclusions

‘Ecosystem-based fisheries management — criteria for the sustainable fishing’ project was started in 2005. The general aims were to define the main factors that affect the state and demography of fish populations, and to develop a strategy for fishing and fish stock management abiding by the principles of sustainable use. The key objectives were to investigate (1) the effects of fishing on abundance, structure, production and genetic characteristics of fish populations, (2) the effects of maternal traits on the amount and quality of offspring, (3) the effects of piscivore fishing on the ecosystem, (4) the factors affecting the interactions between fishes, and (5) the reliability of different methods in estimating fish population abundance and structure. The perch (Perca fluviatilis), pike (Esox lucius) and pikeperch (Sander lucioperca) were chosen as the main target species because they are the most abundant species in the recreational catches in Finland (Natural Resources Institute Finland 2015), but little studied from the abovementioned points of view. The maternal effects (i.e., the effects of female traits on the offspring characteristics) were studied in all three species. Special attention was paid to the role of large individuals in maintaining population renewability and to the effects of different fishing strategies on the food web structure and biological interactions. The experimental study lakes were located in the Evo forest area in southern Finland (61°13 ́N, 25°12 ́E). In addition, studies were carried out in some larger lakes in southern and central Finland (Roikonen 2014, Vainikka et al. 2017). The project was conducted in co-operation by the University of Helsinki and the Finnish Game and Fisheries Research Institute (as of 1 Jan. 2015 Natural Resources Institute Finland), and financially supported mainly by the Bergsrådet Bror Serlachius Foundation.