Diet composition of the small sandeel (Ammodytes tobianus) in the Polish part of the southern Baltic Sea

Abstract

The aim of this survey was to determine the diet composition of the small sandeel (Ammodytes tobianus L.) from coastal waters of the middle coast of Poland. The small sandeel is a fish that is only occasionally caught on an industrial scale in the Polish exclusive economic zone, but it does constitute an important food source for predatory fish, seabirds, and mammals. This species throughout the whole life feeds mostly on zooplankton. The fish for the surveys came from manual trawl hauls carried out in various seasons of the year, between November 2014 and September 2015, in the region of the estuary of the river Łupawa to the southern Baltic Sea. The surveys involved both a macroscopic examination of the stomach fullness degree of the small sandeel and a detailed analysis of its diet composition. Studies results indicated that in the course of the year, over 60% of individuals of the small sandeel had their stomachs filled with food in August, while in the early spring and late autumn their stomachs were often empty. When the samples from all analyzed months were taken into account, the diet of the small sandeel varied and consisted of 26 food components. The basis of the diet was mainly made up of Calanoida: Acartia spp. and Temora longicornis. Moreover, freshwater Cyclopoida had a high frequency of occurrence in the diet of the small sandeel throughout the year of surveys, because as organisms typical for the Lake Gardno, through which the river Łupawa flows, they also occurred in the coastal waters. In May, Harpacticoida also appeared in all analyzed individuals of the small sandeel. Only the largest small sandeels fed on fish larvae and Mysidacea. The diet composition of the small sandeel confirmed that these fish are linked with a specific habitat and do not undertake long-distance food migrations.