Vol. 191: 295-299,1999 l MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published December 30 NOTE Growth of Baltic Sea young-of-the-yearherring Clupea harengus is resource limited Fredrik Arrhenius',', Sture Hansson Department of Systems Ecology. Stockholm Universlty, 106 91 Stockholm. Sweden ABSTRACT: We have determined the in situ food consump- tion rate of young-of-the-year (YOY, length 25 to 94 mm) Baltic Sea herring. This consumption Increased with increas- ing food availablhty, which suggests that the growth rate of young Baltic herring is food lirmted. This has been described previously for larval stages, but not for metamorphosed fish. The daily food consumption rate of YOY herring decreased from about 8 to 15% of body weight for small fish in the sum- mer to 0.6 to 2% for larger juveniles in late autumn. KEY WORDS. Baltic Sea . Juven~les . Herring . Food con- sun~ption . Zooplankton Herring Clupea harengus L. is a dominant predator on crustacean zooplankton in the Baltic Sea (e.g. Hans- son et al. 1990, Rudstam et al. 1992, Arrhenius & Hans- son 1993).It is possible that the effects of this predation indirectly influence other trophic levels (cf. experi- ences from lakes; Carpenter et al. 1985, Carpenter & Kitchell 1993). To evaluate the predation pressure exerted by herring on its prey (Hansson et al. 1990, Rudstam et al. 1992, 1994),food consumption has been estimated from a bioenergetics model, based on physi- ological assumptions and field data on fish growth, habitat temperature, and diet. These analyses have shown that, of the total zooplankton consumption by the Baltic herring population, young-of-the-year (YOY) fish consume 38 to 76%, making them the dom- inant zooplanktivorous age group (Arrhenius & Hans- son 1993, Arrhenius 1997). Although these results in- dicate intensive predation on zooplankton, there are few studies that present a quantitative relationship between food availability and zooplanktivory in the 'Present address. Institute of Marine Research, National Board of Fisheries, PO Box 4, 453 21 Lysekil, Sweden. E-mail: f.arrhenius@imr.se Baltic Sea (Rudstam et al. 1992, Thiel 1996). The ob- jective of this study was to test if such a relationship exists. Materials and methods. Using small charges of ex- plosives (15 to 120 g of Primex 17 mm, Nitro Nobel AB), herring were sampled at approximately 2 h intervals during ten 24 h periods between July and November 1992 and 1993 (data from 1992 are from Arrhenius & Hansson 1994a,b). The explosives were detonated below the fish at varying depths (see Table 1) and explosion gases carried the fish to the surface where they were collected. The depth of the fish was found either empirically, from detonations on different depths, or from an echo sounder. Samples of about 10 fish per length class were taken within 10 min after a detona- tion. In 1992, the fish were immediately preserved in 70% ethanol; in 1993 they were deep-frozen (-18°C). All sampling was done in coastal areas of the northern Baltic proper (around 58" N, 17" E). In the laboratory, the total length of each fish was measured to the nearest mm and the wet weight (WWT) was determined to the nearest mg. Weight data were corrected for effects of preservation (WWT = 0.02 + (1.05 X ethanol-weight [g]), r2 = 0.99, n = 40 and WWT = 0.08 + (1.02 X deep-frozen-weight [g]), r2 = 0.99, n = 200). Fish dry weight (DWT) was estimated as DWT = -0.022 + (0.22 WWT [g]), r2 = 0.99, n = 300. Stomachs were removed and stored in 70 % ethanol for at least 1 mo to stabilise the biomass (Ka rjalainen 1992). Each stomach was cut open, rinsed with ethanol and food particles collected on a glass fibre filter (Whatman GF/F in 1992 and GF/D in 1993).DWT of stomach con- tent was determined to the nearest pg (Sartorius micro M3P) after drying to stable weight at 60°C. We assumed that the zooplankton prey used by the fish were found in the depth interval between the sur- O Inter-Research 1999 Resale of full art~cle not permitted