Reinforcing the native otter Lutra lutra population in East Anglia: an analysis of the behaviour and range development of the first release group

Published source details Jefferies D.J., Wayre P., Jessop R.M. & Mitchell- Jones A.J. (1986) Reinforcing the native otter Lutra lutra population in East Anglia: an analysis of the behaviour and range development of the first release group. Mammal Review, 16, 65-79.
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This study is summarised as evidence for the following.

	Action	Category
	Use holding pens at release site prior to release of captive-bred mammals Action Link
	Provide supplementary food during/after release of captive-bred mammals Action Link

Use holding pens at release site prior to release of captive-bred mammals

A study in 1983–1985 along river on the Norfolk-Suffolk border, UK (Jefferies et al. 1986) found that following the use of holding pens at release sites and short-term provision of supplementary food, released captive-bred Eurasian otters Lutra lutra stayed in their release area for at least two years and bred. Otters survived in the release area at least 28 months after release. Breeding was confirmed the summer after release and suspected again the following summer. Otters held in pens before release displayed similar activity periods, range sizes, and behaviours to those seen in wild otter populations. One male and two female otters (captive-bred and unrelated) were kept in a large pen with a pool where they had limited contact with humans from 10 to 18 months of age. In June 1983, at 18 months, they were moved to a 9 × 15-m pre-release pen, 10 m from a river bank, on a river island. After 20 days, the pen door was fixed open. Food was placed in the pen daily for 12 days after release. The male was radio-tracked from 5 July to 24 August 1983. Otter signs (especially spraints) were then monitored until 1985.

(Summarised by: Ricardo Rocha)
Provide supplementary food during/after release of captive-bred mammals

A study in 1983–1985 along a river on the Norfolk-Suffolk border, UK (Jefferies et al. 1986) found that following the short-term provision of supplementary food after release from holding pens, captive-bred Eurasian otters Lutra lutra survived at the release site for at least two years and reproduced. The otters survived in the release area at least 28 months after release. Breeding was confirmed the summer after release and suspected again the following summer. On the first night, otters were fed prior to being released. They returned to feed on the second, third and fifth to seventh nights but after that food was untouched. Spraint analysis suggested they were catching fish from the fourth night. One male and two female otters (captive-bred and unrelated) were kept in a large pen with a pool where they had limited contact with humans from 10 months to 18 months of age. In June 1983, at 18 months, they were moved to a 9 × 15-m pre-release pen, 10 m from a river bank, on a river island. After 20 days, the pen door was fixed open. Food was placed in the pen daily for 12 days after release in diminishing quantities and uneaten food was cleared away. The male was radio-tracked for 50 days from 5 July 1983. Otter signs (especially spraints) were then monitored until 1985.

(Summarised by: Ricardo Rocha)