BOREAL ENVIRONMENT RESEARCH 26: 89–104 © 2021 ISSN 1797-2469 (online) Helsinki 28 June 2021 Editor in charge of this article: Örjan Östman Rapid effects of a fshing closure on whitefsh (Coregonus maraena) in the northern Baltic Sea Charlotte Berkström 1)2)*† , Ann-Britt Florin 1)† , Ronny Fredriksson 1) , Karl Lundström 3) and Ulf Bergström 1) 1) Department of Aquatic Resources, Swedish University of Agricultural Sciences, Institute of Coastal Research, Skolgatan 6, SE 742 42 Öregrund, Sweden (*corresponding author's e-mail: charlotte.berkstrom@slu.se) 2) Department of Ecology, Environment and Plant Sciences, Stockholm University, SE 106 91 Stockholm, Sweden 3) Department of Aquatic Resources, Swedish University of Agricultural Sciences, Institute of Marine Research, Turistgatan 5, SE 453 30 Lysekil, Sweden † These authors share frst authorship Received 28 Aug. 2019, fnal version received 7 May 2021, accepted 7 May 2021 Berkström C., Florin A.-B., Fredriksson R., Lundström K. & Bergström U. 2021: Rapid effects of a fsh- ing closure on whitefsh (Coregonus maraena) in the northern Baltic Sea. Boreal Env. Res. 26: 89–104. Areas closed to fshing year-round (no-take zones, NTZs) or during spawning time (spawn- ing closures) are used as a management tool to increase declining fsh populations. We evaluated the efects of a 147 km 2 NTZ and a 3980 km 2 spawning closure on whitefsh populations in the northern Baltic Sea, and also accounted for fsh consumption by seals and cormorants. Fish monitoring with multimesh gillnets in 2011–2016 showed a sig- nifcant increase in catch per unit efort (CPUE) of mature whitefsh (> 30 cm) both in the spawning closure and the NTZ compared with the reference area open to fshing. The rate of increase was signifcantly higher in the NTZ than in the spawning closure. Our results suggest that NTZs may strengthen coastal fsh populations in temperate regions and that also seasonal closures under a critical period of the life cycle may beneft the populations. Introduction Fish populations are declining worldwide and attempts to hamper decline has failed in many places including Northern Europe and the Baltic Sea (Zeller et al. 2011; Pauly & Zeller 2016; Froese et al. 2018). In the last decade, there has been some reversal in the downward trend for the internationally managed stocks in the North East Atlantic (Fernandez & Cook 2013; Fernandez et al 2017), however, 69% of 397 European stocks are still subjected to ongoing overfshing (Froese et al. 2018). No-take zones (NTZs), areas where no fshing or other extractive use is allowed, may be a useful regulation to protect and increase these declining fsh populations. This type of reg- ulation has been suggested as a central manage- ment tool in ecosystem-based management and marine spatial planning by providing means of achieving both conservation and fsheries man- agement objectives, where fsh abundance and biomass is expected to increase within the NTZ during the time of closure (Jennings 2009; Gaines et al. 2010; Halpern et al. 2010). From a fsheries perspective, the core mechanisms underlying the success of NTZs is a build-up of fsh densities