Orientation mechanisms in migrating European silver eel (Anguilla anguilla): Temperature and olfaction

Abstract

The migration pattern of silver eel (Anguilla anguilla L.) in the Baltic is well documented from many tagging experiments. This particular investigation differed from previous taggings in that the background of all the eels used was the same. They came from a 1980 stocking programme and had been imported from France as glass eels. When migrating these stocked eels missed the outlet of the Baltic and continued in a south-westerly direction. They were still reported in this southern-most area more than 4 yr later. Indigenous eels turn northwards after passing the south of Sweden and leave the Baltic through the narrow Sound. Since the formerly stocked eels had never been in the Baltic, the absence of an imprinted olfaction cue may explain their orientation failure. Although lacking an imprinted olfaction cue eels were recaptured mainly in a very restricted area in the southwestern Baltic. This reflects another cue, genetic or imprinted during the Atlantic journey. This second cue, temperate, can also serve as the trigger which causes eels to stop migrating and to initiate spawning. The enclosed Baltic acts as a giant trap for eels from the huge stocking programmes undertaken there. As a consequence stocked eels probably contribute little to spawning stocks in the Sargasso Sea which may have contributed to the decrease in abundance of glass eels reported from western Europe in recent decades.