TECHNIQUE

Release of Casualty Seals (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: Halichoerus grypus - Grey seal, Phoca vitulina - Common seal.

These species are within the family Phocidae.

  • The release of seals requires expert advice and equipment; release should always be conducted in conjunction with specialist centres/organisations such as the RSPCA and BDMLR.
  • Be aware that seal releases may attract public attention. Measures should be in place to control any crowds which might collect at the release site, with members of the release team assigned to explaining the release process and ensuring that members of the public are kept away from the animal(s) being released.

Pre-release:

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

  • Tagging and identification markers:
    • Tag with a cattle "rototag" in hind flipper prior to release. (J61.1.w1, P26.2000.w1)
    • Tag before release with tags provided by the Sea Mammal Research Unit. (V.w21)
    • Tags are marked with an identifying number on one side and "Inform London Zoo" on the other.(V.w21)
    • Tagging procedure: administer local anaesthetic in back flipper, make incision in back flipper between two digits, insert numbered tag. (P19.3.w4)
    • The Sea Mammal Research Unit runs a "seal hat" scheme, organised principally to investigate seal pup mortality. This scheme allows individual identification of seals and therefore post-release monitoring. The plastic hat is marked with a unique number clearly visible from a distance with binoculars when the seals head emerges above the water.

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)
  • Criteria for hand-reared pups:

    A range of suggested minimum release body weights for seal pups are reported in the literature. It may be advisable to accept the highest and therefore most conservative release body weight value. The following recommendations have been made:

    • Release at minimum weight Phoca vitulina - Common seal 30-35kg, Halichoerus grypus - Grey seal 40-45kg. (J61.1.w1, P26.2000.w1)
    • Release only when reached at least 25kg (Phoca vitulina - Common seal). (J23.28.w3, P19.1.w6)
    • Halichoerus grypus - Grey seal: More than 30kg weight, in good health and been feeding well without hand feeding for one month.(V.w21)
    • Decision on time for release requires behavioural observation as well as the seal having reached a set minimum weight. (J61.1.w1)
    • Should be able to catch fish to feed themselves when released.(P19.1.w6, J23.28.w3)

Selecting a release site:

  • A suitable site must be carefully chosen for release; release at known seal haul-out site with good feeding grounds nearby. (P19.1.w6, P19.3.w4)

Timing of release:

  • Release in good weather with calm weather expected in the following days.
  • Do not release in bad weather/rough seas.(V.w21)
  • Release when the tide is going out (ebb tide) rather than when the tide is coming in (flood tide).(P19.3.w4)
  • Release at high tide.(V.w21)

Type of release:

  • Seals may be transported on inflatable boats (RIBS) back to colonies for release. (D14)

Hand reared Seals:

  • Transport to release site in suitable, well ventilated container within a van. (see: Wildlife Casualty Handling and Transport)
  • Allow pup to enter the water in its own time.
  • (P19.3.w4)
  • Release on beach, in area with no motor boats; site should be accessible for carrying the seal in e.g. a Sky Kennel. (V.w21)
  • Release from a stationary boat in the water close to an existing seal colony. (J61.1.w1, P26.2000.w1)
Appropriate Use (?)
  • Release back into seal colonies may give a higher chance of survival. (D14)
  • 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.
Notes
  • Release should preferably take place during a period of fine weather.
  • Seals should be tagged prior to release to allow future identification. (P19.3.w4, P26.2000.w1)
    • e.g. plastic cattle rototag in the web of the right hind flipper. (P26.2000.w1)
    • Tagging procedure: administer local anaesthetic in back flipper, make incision in back flipper between two digits, insert numbered tag. (P19.3.w4)
  • The Sea Mammal Research Unit runs a "seal hat" scheme, organised principally to investigate seal pup mortality. This scheme allows individual identification of seals and therefore post-release monitoring. The plastic hat is marked with a unique number clearly visible from a distance with binoculars when the seals head emerges above the water.
  • Licence may be required for some forms of marking. (J35.147.w1)
Complications/ Limitations / Risk
  • Potential hazards with staff working in or near the sea include drowning, hypothermia and physical injury. 
  • 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
  • Considerable information on seal natural history and the local habitats and populations are required for the choice of suitable release sites and time of release.
  • The release of seals requires expert advice and equipment; release should always be conducted in conjunction with specialist centres/organisations such as the RSPCA and BDMLR.
Cost/ Availability
  • Time and equipment required for release including vehicles, transport containers and personnel time may be considerable.
  • 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)
  • Sea shores are potentially hazardous environments. The risks to human health and safety must be remembered: these include sharp rocks, water and the external environment, which may lead to physical injury, drowning, hypothermia or (less commonly in the UK) hyperthermia/sunstroke. All personnel who may work in such conditions must be given adequate training to ensure that they are aware of the risks and know how to minimise these risks.
  • Health and Safety at Work, etc. Act 1974 applies to protect any employees of a wildlife hospital, as well as volunteers at the hospital and visitors. Appropriate safety procedures must be provided to take into account any special risks involved with persons working with non-domesticated species (J35.147.w1, B142.4.w4, B156.21.w21)
Author Debra Bourne
Referee Becki Lawson and Suzanne Boardman
References

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