Critical Assessment of Stocking Experiment on Silver Eel Production and Escapement from the Richelieu River

Experimental stocking was initiated in the Richelieu river to increase spawners escapement of American eel (Anguilla rostrata) as a short-term option to reverse recruitment decline. Between 2005 and 2008, 2.8 millions glass eels were stocked after being marked. A robust monitoring program was set up to assess growth, maturity, and spawning migration for these individuals. Since 2009, when the first migrating silver eels were caught in the estuary, 275 downstream migrants from the 2005 stocking operations were sampled for analysis. Mean length at silvering was 655.2 mm (SD = 51.2), a size 300 mm smaller than their natural-recruited counterparts and they remained shorter over the five sampled years. The first migrants sampled were 4-years old and exhibited a very rapid growth. Mean annual growth decreased later and was inversely correlated to age at migration. Abundance increased from 2009 to 2012 and remained the same in 2013 indicating that most of the stocked eels were silvering at age 7 and 8 as opposed to those naturally recruited at age-20. They showed a 20 days delay during the migration season  in the estuary, only 500 km from stocking location, which may have implications for reproduction synchrony in the Sargasso, 3500 km further.