Release of Casualty Lutra lutra - European otter (Wildlife Casualty Management)

Summary Information
Type of technique Health & Management / UK Wildlife Casualty Management / Techniques:
Synonyms and Keywords N.B. This information should be read in association with Wildlife Casualty Release which contains background information together with links to the Electronic Library and Organisations (UK Contacts). The related Species pages contain similar linkages.
Description This page has been prepared for the "UK Wildlife: First Aid and Care" Wildpro module, and is designed for the needs of the following species: Lutra lutra - European otter


  • No pre-release preparation is required if these animals have been in care for a short period of time.

Release assessment/criteria:

  • Released mammals:

    • Must be able to recognise, catch, manipulate, consume and digest their natural diet.
    • Must be capable of normal locomotion (movement) and have sufficient fitness for sustained activity.
    • Must have adequate sensory ability (sight, smell, hearing, touch).
    • Must be of an appropriate weight for the age, sex, and time of year. 
    • Must have a satisfactory hair coat.
    • Must show appropriate wariness of humans and domestic animals.
    • (P19.1.w10, P24.233.w11, J35.147.w1, D27)
  • Appropriate health checks should be carried out prior to release. A careful assessment (risk analysis) must be made as to the risks of released animals introducing novel pathogens (disease agents) into the wild population/environment.
    • These pathogens may have been acquired from domestic animals, other wildlife casualties or humans whilst the animal was in captivity.
    • The health checks should be designed to minimise the risk that pathogens posing a threat to wild populations of this or other species will be introduced into the environment when the animal is released.
    • (V.w5, V.w6, P28.2000.w1, J15.20.w3)

Selecting a release site:

Hard release:

  • Release adults back into their own territory, at the safest suitable site to the site of origin.

(P19.3.w3, D24, D27)

Soft release:

  • Select release area carefully. Suggested criteria are:
    • "possession of good habitat.
    • sufficient habitat to accommodate successive groups of otters over several years.
    • an adequate food supply.
    • no serious pollution problems.
    • a minimum of potential points of conflict such as fish farms.
    • widespread acceptance of a release programme by landowners and other interest groups.
    • a sub-optimal otter population in need of reinforcement.
    • a reliable local assistant." (P19.3.w3)
  • Information from both national and local surveys may be required to provide adequate data to identify suitable release sites.(P19.3.w3)
  • Contact expert organisations such as the International Otter Survival Foundation and The Otter Trust for advice.

Timing of release:

  • Release adults as soon as possible.
  • Release at dusk.
  • (P19.3.w3, D24)
  • Release may best be carried out when the cub reaches the normal age for dispersal from its mother, or delayed until spring if this would mean a winter release. (D51)

Type of release:

Hard release:

  • Release back into own territory as soon as possible.
  • Release at dusk.
  • (P19.3.w3, D24)

Soft release:

  • Required for hand-reared orphaned otters.
  • Build the release pen at a secluded site.
  • Release pen may be constructed from 75cm high fencing with an electric wire; plastic netting with a single electrified strand of wire near ground level just inside the netting has been used successfully.
  • Accustom animals to the electrified fence prior to moving to the release pen.
  • Transfer animals to the release pen within their own, familiar sleeping boxes.
  • Allow animals to acclimatise at the release site for three weeks prior to release.
  • Provide fish within the pen after release; otters may return for up to two weeks. (P19.3.w3)
  • The length of time for which individuals return for food is variable.(D51)
  • (P19.3.w3, D51)
Appropriate Use (?)
  • Soft release is particularly important for hand reared animals, particularly of species which need to learn about their surroundings (e.g. food sources) and/or learn survival skills such as hunting.
  • Soft release is also suitable for animals which have been in care for prolonged periods.
  • Soft release may compensate for difficulties of newly released animals finding food and shelter, particularly in a new environment and/or at a time of reduced physical fitness/stamina.
  • Hard release is most appropriate for animals which have been held in captivity for only a short time, for adult animals and for animals being released back into their own territory.
  • The individual animal must, at the the time of release, be healthy, have a reasonable level of fitness and be able to fend for itself in the wild.
  • Diurnal species should be released in the morning, giving them a full day to explore and look for food and shelter before nightfall.
  • Nocturnal species should be released at night.
  • Release should preferably take place during a period of fine weather.
  • Radio-tracking has been used to monitor post-release behaviour of hand-reared cubs.
  • A subcutaneous transponder may be implanted to allow the future identification of an individual casualty.
Complications/ Limitations / Risk
  • Hard release is least appropriate for juveniles which have been hand reared, particularly species for which learning about their environment and/or social skills are important.
  • Hard release may also be inappropriate for adults which have been maintained in captivity for prolonged periods and/or are being released at a site distant from their original location.
  • Released animals may be at risk of contracting disease if there is an ongoing disease problem in the wild population at the time of release.
  • The wild population may be at risk from novel pathogens (disease agents) carried by a rehabilitated animal. These pathogens may pose the greatest threat to free-ranging populations if the animal is to be released at a site distant from its original location therefore increasing the likelihood of spread of disease. It is important to remember that the casualty wild animal may have acquired disease from domestic animals, other wildlife casualties or humans whilst in captivity. 
Equipment / Chemicals required and Suppliers
Expertise level / Ease of Use
Cost/ Availability
  • Soft release may involve a considerable time investment.
  • Soft release may be expensive in terms of construction of appropriate temporary accommodation at the release site.
  • Costs of appropriate health screening.
Legal and Ethical Considerations
  • The potential risks to the individual being released and to the wild population into which it is being released (also to domestic animals) must be considered before release is undertaken.
  • The potential risk to humans and pets from habituated/tame individuals must be considered.
  • An offence may be committed under Section 1 of the Abandonment of Animals Act 1960 if a released rehabilitated animal does not have a reasonable chance of survival (i.e. a chance similar to its non-rehabilitated peers). 
    • This may include release at an unsuitable site, in the wrong territory, unfit, not having learned to hunt, at the wrong time of year etc. 

(J35.147.w1, B156.21.w21, B223, W5.Jan01)

Author Debra Bourne
Referee Becki Lawson and Suzanne Boardman

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