The general distribution pattern and mixing probability of Baltic sprat juvenile populations Hans-Harald Hinrichsen a, * , Gerd Kraus a , Ru ¨diger Voss a , Daniel Stepputtis a , Hannes Baumann b a Leibniz Institute of Marine Sciences, Du ¨sternbrooker Weg 20, D 24105 Kiel, Germany b Institute of Hydrobiology and Fisheries Science, Hamburg, Germany Received 21 February 2005; accepted 21 June 2005 Available online 8 September 2005 Abstract Transport of Baltic sprat Sprattus sprattus L. larvae spawned on different spawning grounds was investigated by detailed drift model simulations for the years 1979–2002. Modeling approaches with and without diurnal vertical migration were applied. We used recently collected data on spawning location, vertical distribution and the timing of spawning as input to a particle tracking model. Results of this modeling study enabled the identification of potential nursery grounds for sprat originating from different spawning grounds. On average, westerly winds are prevailing over the Baltic Sea. This leads to on average higher abundance of juvenile sprat along the southern and the eastern coast lines of the Baltic. The horizontal distribution of simulated larval or 0-group sprat is consistent with the observed distribution of 0-group sprat obtained from the hydroacoustic field surveys. In addition, this analysis identifies the potential for advective mixing between juveniles originating from different spawning sites or from the same spawning site throughout the spawning season. High spatial overlap was found between Arkona- and Bornholm Basin larvae hatched at the beginning of the spawning season. Mixing probability of sprat juveniles between Arkona- and Gotland Basin as well as between Bornholm- and Gotland Basin were on relatively low levels. D 2005 Elsevier B.V. All rights reserved. Keywords: Hydrodynamic modeling; Advective mixing; Hydroacoustics; Sprat nursery grounds; Spatial overlap analysis 1. Introduction The maintenance of distinct stocks of one species requires that juveniles recruit to their source popula- tion and that mixing between stocks is restricted. However, many fish stocks are sedentary as adults but are redistributed as juveniles by currents during 0924-7963/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2005.06.003 * Corresponding author. Tel.: +49 431 600 4566; fax: +49 431 600 4553. E-mail address: hhinrichsen@ifm-geomar.de (H.-H. Hinrichsen). Journal of Marine Systems 58 (2005) 52 – 66 www.elsevier.com/locate/jmarsys