Sprats, Baltic

Biryukov, N.P. (1980). Baltic sprat Biological Condition and Commercial Use (In Russian). Leningrad University Press, Leningrad, 142 pp. 

Ipatov, V.V. and Kondratyeva, N.M. (1986). Bioenergy aspects of ecology of Baltic sprat. Fischerei-Forschung, Rostock 24,52-54. 

Diekmann, M., Mollmann, C., Voss, R., 2007. Feeding ecology of Central Baltic sprat (Sprattus sprattus L.) larvae in relation to zooplankton dynamics—impheations for survival. Marine Ecology Progress Series, 342, 277-289. 

Voss, R., Clemmesen, C., Baumann, H., Hinrichsen, H. H., 2006. Baltic sprat larvae coupling food availability, larval condition and survival. Marine Ecology Progress Series, 308, 243-254. 

Domiszewski, Z. and Kofakowska, A., 2001, Heating-induced changes in fatty acid composition of fresh and frozen Baltic sprat at 100°C, presented at 24th World Congr. ISF, Berlin, September 16-20, 54. 

Because of the large-scale biomanipulation experiment of the twentieth century, the Baltic Sea should therefore be a fish and fisheries paradise. And in fact for sprat and herring it seems to be (Fig. 18.2). So much so that they are now competing among themselves for food and may even be inhibiting recovery of the cod population. Additional details of these interactions, and the role of climate on their regulation, are described below. 

FIGURE 18.13 Scheme summarizing the processes leading to the present low cod/high sprat ecosystem in the central Baltic Sea grey arrows indicate salinity/oxygen-driven processes, hlack arrows indicate temperature-driven processes, dotted hlack arrows indicate a trophic cascade from cod to sprat and Pseudocalanus acuspes, F Fishery, C Cod, SPR Sprat, PS P. acuspes, AC Acartia spp. 

Fishery and hydrography are obviously the major driving forces of the fate of the eastern Baltic cod stock. In the absence of a large foraging cod stock, sprat stocks thrive, foraging themselves on the food of cod larvae and on cod eggs as well, leading to a sprat-dominated ecosystem (Fig. 18.14). 

FIGURE 18.14 Schematic presentation of processes stahi lizing a cod or sprat dominated system in the central Baltic. Note the vertical line represents the situation in the second half of the 199O s with the regime shift taking place in the late 198O s and the early 199O s (from Koster et al., 2003). 

Second, the populations of herring and sprat would decrease because of an increase in predation (Koster et al., 2001, 2003). As a consequence of their decrease in population size, the density-dependent competition within and among these species for zooplankton prey (Mollmann et al., 2005 Casini et al., 2006) would decrease. This should subsequently lead to an increase in their growth rates and condition (Mollmann et al., 2005 Casini et al., 2006). Given that the demand by humans for Baltic herring has partly decreased because of their lower condition, larger and better-conditioned herring would make these fish more attractive to human consumers. 

FIGURE 18.15 Spawning stock biomasses of cod and sprat of the Baltic Sea and cod of the central Baltic Sea. Mind the different ordinate scales for sprat and cod, data derived from ICES (2006). 

FIGURE 18.16 Concentrations of PCBs (a) in Baltic herring, sprat, and salmon muscle and (b) in cod liver (MacKenzie et al., 2004). Error bars represent two standard errors. 

In this chapter, we review fishing history and climate effects on cod, sprat, and herring stocks considering effects of the fishery and physical environment on stock development and the reproductive success, recruitment, and growth. Finally, the potential for the recovery of the eastern Baltic cod stock and the benefits of a more balanced ecosystem are discussed. 

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