Yield per recruit from stocking two different sizes of eel (Anguilla anguilla) in the brackish Roskilde Fjord

Published source details Pedersen M.I. & Rasmussen G.H. (2016) Yield per recruit from stocking two different sizes of eel (Anguilla anguilla) in the brackish Roskilde Fjord. ICES Journal of Marine Science, 73, 158-164.
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This study is summarised as evidence for the following.

	Action	Category
	Release wild-caught captive-reared eels to re-establish or boost native populations ('head-starting') Action Link

Release wild-caught captive-reared eels to re-establish or boost native populations ('head-starting')

A study in 2001–2011 at a fjord in Denmark (Pedersen & Rasmussen 2016) found that wild-caught captive-reared European eels Anguilla anguilla released at two different sizes had similar mortality rates, and small eels grew faster than large eels. During 3–8 years after release, average annual mortality rates did not differ significantly between captive-reared and released large (64%) and small eels (52%). Released small eels had greater average annual growth rates (52 mm) than large eels (44 mm). During 2–13 years after release, recapture rates of captive-reared and released eels were estimated to be 13% for small eels and 9% for large eels (difference not statistically tested). In July–September 1998 and June–July 1999, European eels of two sizes (large: 8–9 g, total 50,000 eels; small: 3 g, total 274,000 eels) were tagged and released into a brackish fjord (water depths of 1–3 m over vegetation or soft bottom). All eels had been imported as glass eels from France and reared in an aquaculture facility for 3–6 months before release. In 2001–2006, a proportion of commercial fisheries catches (15%) were checked for tagged eels. Recaptured eels were weighed and measured in length. Recapture rates for 2007–2011 were estimated using growth and mortality rates. 

(Summarised by: Anna Berthinussen)