Sprat Feeding in front of the Bulgarian Black Sea Coast

This study i focused on identification of the main components of sprat diet in early summer and analysis of the temporal variations in feeding patterns in the western Black Sea. Four trawl surveys were performed during 2007 - 2010 (similar to 35 trawls included in one survey), as 15 - 25 sprat specimens per each trawl catch were randomly selected and preserved in 10 % formaldehyde seawater solution. Under laboratory conditions the absolute length and weight of sprat specimens were measured, the stomachs and food mass were weighted; feeding incidence and diet composition were estimated. The indexes of stomach fullness and relative importance of zooplankton species were calculated for quantitative analysis of the temporal changes in sprat feeding. The sprat diet was constituted by Calanus euxinus, Acartia clausi, Pseudocalanus elongatus, Paracalanus parvus, Centropages ponticus, Oithona spp., Pleopis polyphemoides, Parasagitta setosa, Ostracoda, Oikopleura dioica, Lamellibranchia veliger, Decapoda larvae and Cirripedia larvae. The primary food source for sprat - cold-water copepod Calanus euxinus represented high proportion - 68,50 % in ration in 2008, middle levels (similar to 50 %) in 2007 and 2009, while its share has decreased up to 20,81 % in 2010. The sprat diet showed great diversity in 2010, due to abundance of small warm-water and euryterm zooplankton. Nutrition based on small-sized zooplankton could not provide enough energy for growth and the sprat mean weight remained low during the survey in 2010, implying unfavourable feeding conditions. We established significant temporal variation of sprat weight and nutritional indexes, suggesting influence of the environmental conditions on the sprat population parameters and feeding.