Publication Abstract

Individual biological traits of silver European eels sampled across the species geographic range were measured to assess the reproductive “quality” of the eels – eg. an expression of their ability to migrate, to breed successfully and to produce a viable offspring – in relation to geography, catchment characteristics and contamination with a broad range of metals and persistent organic pollutants. We sampled 13 different catchments from Sweden to Spain, and flowing to the Baltic, the North Sea, the Atlantic Ocean and the Mediterranean Sea. For each eel the quality was inferred from a large range of life history traits derived from biometric measurements (ie length, weight, eye diameter, pectoral fin dimensions, girth), estimated age from otoliths, calculated condition indices (ie, body condition, fat content, GSI, HSI), measured hormonal status (11kt) and undertook otolith microchemistry to determine the life history of each eel. The parasite loads, including Anguillicoloides crassus but also monogeans and Acanthocephalus., were also determined. These characteristics are combined to provide assessment of the eels’ “quality”.  Our results, which represent the most comprehensive assessment of silver eel quality undertaken to date, will enable us to explore the general patterns of age and size at silvering, life history traits and “quality” of eels and the possible effects of contamination. These results underline the requirement to take regional differences in life-history into account when designing Europe-wide management measures to protect eel populations.