European eel restocking programs based on wild-caught glass eels: Feasibility of quarantine stage compatible with implementation of prophylactic measures prior to scheduled reintroduction to the wild

Published source details Delrez N., Zhang H., Lieffrig F., Mélard C., Farnir F., Boutier M., Donohoe O. & Vanderplasschen A. (2021) European eel restocking programs based on wild-caught glass eels: Feasibility of quarantine stage compatible with implementation of prophylactic measures prior to scheduled reintroduction to the wild. Journal for Nature Conservation, 59, 125933.
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This study is summarised as evidence for the following.

	Action	Category
	Change capture, transport or release methods to increase survivorship of translocated (‘stocked’ or ‘restocked') eels Action Link

Change capture, transport or release methods to increase survivorship of translocated (‘stocked’ or ‘restocked') eels

A replicated study in 2017–2018 at a laboratory in Belgium (Delrez et al. 2021) found that wild-caught European glass eels Anguilla anguilla had higher survival rates following release into outdoor basins after quarantine periods of 15 rather than 30 days, and providing food or modifying water temperatures during quarantine had no effect on survival rates. In each of two years, average eel survival rates were higher following release after a 15-day quarantine period (2017: 99–100%, 2018: 98–99%) than a 30-day quarantine period (2017: 95–97%, 2018: 91–94%). Survival rates during quarantine did not differ significantly between eels that were fed (2017: 99–100%, 2018: 98–99%) or not fed (2017: 99–100%, 2018: 100%), or kept in tanks with water temperatures of 20°C (2017: 95–99%, 2018: 94–100%) or 24°C (2017: 97–100%, 2018: 91–100%). Glass eels were wild caught in estuaries in France (2017) and the UK (2018) and transported to the laboratory. After acclimatization, 400 eels were transferred to each of six 40-l quarantine tanks containing PVC pipes. Eels were quarantined for 15 days (four tanks) or 30 days (two tanks). Water in half of the six tanks was kept at 20°C, and half at 24°C. Eels in half of the tanks quarantined for 15 days were provided with food (cod roe and pellets), while the other half were unfed. Following quarantine, three groups of 50 eels were transferred from each tank to separate plastic cages randomly placed in three outdoor basins (110 cm long x 110 cm wide, 33 cm water depth) containing groundwater. Surviving eels were counted after 15 days.

(Summarised by: Anna Berthinussen)