Survival and behaviour of European silver eel in late freshwater and early marine phase during spring migration

The seaward migration of European silver eel Anguilla anguilla (L.) was studied during the late freshwater and early marine phase in River Gudenaa and Randers Fjord, Denmark, in the spring 2004. Migration was monitored in sections with different physical characteristics over a total distance of 46 km using automatic listening stations. Generally, eels quickly left the River Gudenaa (67% within 2 days) and stayed for up to 4.3 months (mean 1.7 months) in the inner fjord. This indicates a two-step migration, with silver eels migrating out of the river in the spring, followed by a substantial residence period in the inner part of the fjord before continuing the migration. The results suggest that silver eel migration may not always be a direct journey to the ocean, but may include resident periods in coastal areas. The eels were subjected to a high mortality with less then 20% surviving out of the fjord. Fishing seemed to be the main reason for the mortality.