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EN
The abundance of the sardine in the North Sea suddenly increased after 1995. Since 2002, the sardine has been spawning regularly in the German Bight, and all its life stages can be found in the area. The larval feeding ecology of two small pelagic clupeiform species with very similar life histories was investigated, the particular aim being to determine signs of food overlap. The distribution and feeding of sprat and sardine larvae were investigated during late spring 2003 on two transects covering a wide range of environmental conditions in the German Bight. Larvae co-occurred at all the stations investigated. Sprat and sardine larvae shared a wide range of prey types. Gut fullness and feeding success were similar in both species; however, potential food competition is avoided to some extent by different habitat preferences.
EN
Existing coupled biophysical models for Baltic larval cod drift, growth and survival use idealised constructed mean prey fields of nauplius distributions. These simulations revealed the best feeding conditions for Baltic cod larvae longer than 6 mm. For shorter, first feeding larvae (between 4.5 and 6 mm) pronounced differences in growth and survival were observed, which depend on food availability and to a lesser degree on ambient temperature. We performed runs with an Individual-based Model (IBM) for Baltic cod larvae in order to demonstrate how natural variability in prey abundance influences the survival success of first feeding larvae. In the Baltic, this larval stage lives mainly between 20 and 40 m depth and feeds exclusively on the nauplii of different calanoid copepods (Acartia spp., Pseudocalanus acuspes, Temora longicornis and Centropages hamatus). Prey data obtained from vertically stratified samples in the Bornholm Basin (Baltic Sea) in 2001 and 2002 indicate a strong variability at spatial and temporal scales. We calculated larval survival and growth in relation to natural variation of prey fields, i.e. species-specific nauplius abundance. The results of the model runs yielded larval survival rates from 60 to 100% if the mean size of nauplii species was taken and lower survival if prey consisted of early nauplius stages only.
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