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Providing evidence to improve practice

Individual study: Surrogate-reared southern sea otter Enhydra lutris pups have greater survival rates in the wild than pups reared without surrogates, California, USA

Published source details

Nicholson T.E., Mayer K.A., Staedler M.M. & Johnson A.B. (2007) Effects of rearing methods on survival of released free-ranging juvenile southern sea otters. Biological Conservation, 138, 313-320


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Place orphaned or abandoned wild young with captive foster parents Terrestrial Mammal Conservation

A controlled study in 1986–2004 at an aquarium and coastal site in California, USA (Nicholson et al. 2007) found that stranded sea otter Enhydra lutris pups reared in captivity by foster mothers began foraging earlier and had greater survival in the wild than unfostered pups, and similar survival to wild pups. Fostered sea otter pups began foraging independently on live prey at younger ages (average 8–19 weeks old) than unfostered pups reared mostly alone (average 11–22 weeks old). A greater proportion of fostered pups survived at least one year after release (5 of 7 pups; 71%) than unfostered pups (8 of 26 pups; 31%), and survival was similar to wild pups (9 of 12 pups; 75%). In 2001–2003, seven stranded sea otter pups were brought into captivity and reared with adult female sea otters. In 1986–2000, twenty-six stranded sea otter pups were reared in captivity without foster mothers (mostly alone). All pups were rehabilitated at the same aquarium. Before release, pups were implanted with radio-transmitters and individually tagged. After release in 1987–2004, the rehabilitated otters were monitored daily during the first month and then twice weekly for up to 12 months. Twelve wild juvenile male sea otter pups were observed during a field study prior to 2003 (date not reported).

(Summarised by Ricardo Rocha)

Hand-rear orphaned or abandoned young in captivity Terrestrial Mammal Conservation

A study in 1986–2000 in an aquarium in California, USA (Nicholson et al. 2007) found that approximately one-third of rehabilitated sea otter Enhydra lutris pups released back into the wild survived for at least one year. Eight of 26 (31%) rehabilitated sea otter pups reared in captivity survived for at least one year after release. The other pups died (16 pups; 11 of which died within one month of release) or had to be permanently returned to captivity (two pups). In 1986–2000, twenty-six stranded new-born sea otter pups were brought into captivity and rehabilitated. Pups were raised primarily in isolation (60–80% of their time during rehabilitation) but were introduced to other sea otters at 9–18 weeks old. Before release, pups were implanted with a radio-transmitter and individually tagged. After release in 1987–2000, rehabilitated otters were monitored daily from shore during the first month and then twice weekly for up to 12 months.

(Summarised by Ricardo Rocha)