Do glass eels restocked in winter have a lower survival rate than glass eels restocked in spring?

Published source details Simon J. (2023) Do glass eels restocked in winter have a lower survival rate than glass eels restocked in spring?. Fisheries Research, 266, 106784.
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This study is summarised as evidence for the following.

	Action	Category
	Translocate wild eels to re-establish or boost native populations (‘stocking’ or ‘restocking’) Action Link

Translocate wild eels to re-establish or boost native populations (‘stocking’ or ‘restocking’)

A study in 2010 and 2020–2021 in five lakes in Brandenburg, Germany (Simon 2023; same sites as Simon & Dörner 2014) reported that less than half of translocated wild European glass eels Anguilla anguilla released in winter survived for 3–4 years, and survival rates were similar to translocated wild eels released in spring. Results are not based on tests of statistical significance. After 3–4 years, the percentage of eels surviving in each lake was estimated to be 19–45% for translocated eels released in winter and 9–45% for translocated eels released in spring. During winter in February 2017, translocated wild glass eels (370 eels/ha, average 0.3 g/eel) were released in five lakes (each <20 ha, water temperatures 1–5°C). Eels were tagged and marked before release. In April–June 2020 and 2021, eels were recaptured by electrofishing from a boat along the entire shoreline on 6–8 occasions/lake. Data were compared to previously published survival estimates for translocated wild eels released at the lakes in spring 2006 and 2007 (200 eels/ha, average 0.3 g/eel; water temperatures 6–18°C), and recaptured in April–June 2010.

(Summarised by: Anna Berthinussen)