Download Management Strategies: Stoat (Mustela erminea)

Management: Stoat (Mustela erminea)
Compiled by the IUCN/SSC Invasive Species Specialist Group (ISSG)
Contents :
1. General Considerations

Applicability of control
2. Monitoring / Tracking

Tracking tunnels
3. Preventative Measures

Exclusion fencing
4. Physical Control



Trapping
Bait use
Use of trained dogs
5. Chemical Control


Brodifacoum (Talon®), sodium monofluoroacetate (1080)
Public perceptions
6. Biological Control

New Zealand Government biocontrol research fund
7. Information Access

International bibliography of stoat information
8. Integrative Management


Monitoring threatened species
Detecting breeding success of threatened species
9. Research


Use of lures
Bait formulation
10. Ethical Considerations


Ethical dilemmas
New Zealand legislation
1. General Considerations
King (1984) concluded that stoat control is probably only worthwhile (in New Zealand)
in specific situations, namely during the nesting season and only for the protection of a
few endangered bird species that are most adversely affected by stoat predation (in
Lawrence and O.Donnell 1999). This extract is edited from King (1994):
To plan a mustelid control or monitoring operation, it is necessary to:
 Be familiar both with the conservation landowner’s general policy on
pests, and also with the national strategy for mustelids
 Have a clear understanding of the local problem, and with any native
species to be protected
 Set clear and achievable objectives, and
 Choose appropriate field techniques that will serve the objectives and
assess whether they have been met.
To operate the chosen plan, it is necessary to:
 Develop experience in the efficient use and maintenance of the field
techniques to be used
 Keep systematic records on what has been done,
 Note and think about any potentially significant observations made
during the course of routine field work.
2. Monitoring / Tracking
Stoats (Mustela erminea) can be detected via tracking tunnels, which conservation
managers and researchers at mainland sites throughout New Zealand are now using to
index mustelid numbers (Gillies and Williams Unpub.).
3. Preventative measures
Clapperton and Day (2001) found that the costs of exclusion fencing for stoats using the
Xcluder™ design of multi-species pest-proof fence is effective and cost-efficient in large
reserves of 5000 ha or more and on peninsulas. In such locations the cumulative costs of
conventional control methods exceeds the initial cost of a fence set up (plus maintenance
costs) in as little as four years. Electric fences may also be used but may be prone to
failure (Clapperton and Day 2001).
4. Physical Control
Trapping is a widely used method to control stoats in the United Kingdom and New
Zealand. Intensive trapping is effective but may be rapidly countered by re-invasion from
surrounding areas (McDonald and Harris 2002). Control via trapping was attempted in
New Zealand to protect the takahe Notornis mantelli. Traps were set in a line at 200 m
intervals in Takahe Valley, however, they had little effect on the stoat population, and
takahe numbers continued to decline (Lavers and Mills 1978, in Dilks et al. 1996).
Leg-hold traps are still legal in some countries but are likely to be banned. The Fenn is a
relatively humane trap developed in United Kingdom in the 1950s. In fact, at least four
kill traps tested have proven to be less than satisfactory at delivering a (relatively)
humane death, namely the Fenn Mk IV, Fenn Mk VI and Victor Snapback (Warburton
and Connor 2004) (see 10. Ethical Considerations).
The cost of stoat control is also likely to be prohibitive, however, perimeter trapping
layouts may reduce costs. Perimeter tapping around a 100 hectare block has been proven
experimentally to be as effective at achieving high stoat catch rates as setting traps in
intensive 100-meter-spacing lines (Lawrence and O.Donnell 1999). However, this
experiment was conducted in a situation of low stoat density and may not be applied to
higher stoat densities.
Baits for traps are often based on the food source that is available to the target animal
(Hamilton 2004). This can be the prey item of highest abundance within an area and can
vary from season to season, eg: rabbit, possum or mouse (Hamilton 2004). Other food
items such as eggs (Dilks et al. 1996, Dilks and Lawrence 2000, in Hamilton 2004),
commercially mixed baits, fish paste, and pet food have been used in New Zealand. In
many cases the choice of type of bait is more for ease of operation and the long-life
properties of the bait than for its attractant capabilities (Hamilton 2004).
Locating natal stoat dens using trained dogs and controlling female stoats and young
inside (by pellet use and sealing of holes) is a potentially effective control method which
may reduce the summer influx of young stoats into an ecosystem. Theobald and Coad
(2002) trialled this method in Trounson Kauri Park, New Zealand, to protect newly
hatched kiwi chicks. However, the results of this study were not promising (possibly as
not all entrances were sealed off or the pellets used were not appropriate).
5. Chemical Control
Sodium monofluoroacetate (1080) poisoning, which is described as causing death ‘from
heart and lung failure within 12 hours’ is perceived as more acceptable method of stoat
control by the public than Talon® (brodifacoum), which is described as ‘a common rat
poison’ causing death ‘from internal bleeding within a week’ (according to a survey
conducted by Fitzgerald, Fitzgerald and Wilkinson 2005). However while views about
Talon® use may be clearer and more negative than about 1080 a large number of
respondents (40%) still found 1080 to be an unacceptable stoat control method.
The use of cholecalciferol (registered in New Zealand as FeraCol®) to kill stoats was
studied experimentally by Spurr et al. 2002 to test palatability of bait formulations Death
by this route does not appear to be pleasant, with the toxin inducing the stoat to stop
feeding after one day, lose weight and die via organ failure within about a week. The
authors also suggest cyanide, diphacinone, zinc phosphide, or MNT.
6. Biological Control
Because of continuing concerns about the impact of stoats on the nation’s biodiversity,
especially its avifauna, the New Zealand Government created, in 1999, a special five-year
fund for research into the control of stoats. The project considered biological control
methods such as canine distemper virus, potential mustelid-specific diseases, and possible
techniques for controlling the fertility of stoats which could require the genetic
modification or ‘engineering’ of organisms for use in biological control. However in a
public survey on attitudes toward stoat control Fitzgerald, Fitzgerald and Wilkinson
(2005) found a lack of support for this method. This was probably due to negative
attitudes towards and public debate over the genetic modification of organisms. Despite
this animal welfare is an important factor in the selection process for possible biological
control options (Fitzgerald Wilkinson and Saunders 2000; Lenghaus et al. 1994, in Littin
and Mellor 2005).
McDonald and Lariviere (2001) reviewed the literature on the diseases and pathogens of
stoats, and closely related mustelids, with a view to identifying potential biological
control agents. They found that Aleutian disease virus, mink enteritis virus, and canine
distemper virus hold promise as agents of lethal control, though the risks to non-target
species posed by these viruses are serious. Host-specific ectoparasites such as
Tnchodectes ermineae, nematodes such as Skrjabingylus nasicola, and bacteria such as
Hehcobacter mustelae and Bartemella spp could have a role as vectors for the
transmission of fertility control agents (McDonald and Lariviere 2001).
7. Information Access
An international bibliographic database of 1213 papers, notes, books and unpublished
reports on stoats and two related species (Mustela erminea, weasel M. nivalis and
common weasel M. frenata) dating from between 1877 and 2004 is available as a simple
reference list at http://bio.waikato.ac.nz/staff/bibliography.pdf. It is also available in a
searchable, interactive form on the following Australian based website: www.feral.org.au
(which also provides information on other invasive species). It is interesting to note that
New Zealand is now the world centre for research on mustelids, especially stoats
8. Integrative Management
Stoat control often goes hand in hand with monitoring recovery rates of threatened or
native species. At Dart Valley, New Zealand, a site of southern beech (Nothofagus spp.)
forests populations of threatened mohua (yellowhead) Mohoua ochrocephala are at risk
from the stoat population. Lawrence and O’Donnell (1999) recommend measuring
increases in the breeding success of mohua to detect positive outcomes of stoat control
(decreased predation rates and increased nesting success).
9. Research
Research into the use of new baits and lures is substantial (a few examples are discussed
below). However, primary data is lacking and in the population biology of stoats with the
notable exception of stoat populations in southern beech Nothofagus spp. mast cycles
(New Zealand) (McDonald and Lariviere 2001). Understanding the relationships between
stoat density and bird survival is needed for the development of novel biotechnological
stoat control methods (McDonald and Lariviere 2001) and, perhaps, to justify such
research. Such studies may contribute to an understanding of the effects of new stoat
control methods/agents on predator (ie: stoat) and prey (ie: bird species) populations.
After initial data is collated computer simulation modelling may prove a powerful tool in
determining the impact of a range of control strategies on stoat populations and the birds
they prey on (Courchamp and Sugihara 1999, in McDonald and Lariviere 2001).
More attractive lures and acceptable baits are required to improve the efficacy of stoat
control in New Zealand (and elsewhere). Apparently traps with bright covers (yellow and
red) are more attractive to stoats than those with duller covers (green and black)
(Hamilton 2004). A series of preference trials by Robbins and colleagues (2007) on
captive stoats to determine the potential of various visual, textural, and movement cues in
lures and baits found the following: (i) bait colour does not affect bait consumption, (ii)
mouse-shaped bait with realistic eyes are more readily eaten than disk-shaped bait, (iii)
possum fur increases the palatability of wax baits, but not of already palatable bait, (iv)
concave mirrors are attractive lures, however, the presence of egg lures is more
important, (v) red light-emitting diodes do not increase investigatory responses and,
finally, (vi) moving baits attached to a pendulums may direct the attention of stoats
towards baits/control devices.
Improved, cost-effective stoat control methods are needed to reduce stoat predation on
New Zealand wildlife. Clapperton and colleagues (2006) tested the attractiveness and
palatability of a range of lures and baits on captive stoats. Prey-based lures were the most
attractive. The authors failed to find additional odours that would enhance lure success.
Highly palatable baits included gelatine-injected freeze-dried mice and a
wax/tallow/rabbit meat mix. These effective baits can be used as alternatives to eggbased baits to increase variety and counter bait-shyness (Clapperton et al. 2006). The
addition of sodium meta-bisulphate to bait produces attractive, palatable baits with a field
life of at least one week (Clapperton et al. 2006).
10. Ethical Considerations
Stoats are cute. Many people are horrified at the thought of killing these animals. This
poses an ethical dilemma. Sometimes certain values must be compromised in order to
preserve other values such as the conservation of the environment. In this case reducing
predation by stoats is clearly essential for the survival of several endemic species on the
mainland of New Zealand, such as kiwi Apteryx spp., kokako Callaeas cinerea, takahe
Porphyrw hochstetteri, mohua Mohoua ochrocephalus, kaka Nestor meridionalis and
kakariki Cyanoramphus spp. (McDonald and Lariviere 2001; Dilks et al. 1996). This is
because the irregular but severe predation by stoats on native birds has been implicated in
their decline (Elliott and O'Donnell 1988, Donnell 1996, in Dilks et al. 1996).
Whatever ones’ views on this issue, there is one thing everyone should agree about: if an
animal is to be killed it should be done humanely and, if possible, expertly. Some of the
trapping methods discussed in the literature are probably far from humane and more
research needs to be conducted in this area. For example, kill traps have been assessed
against the specifications that target animals must be rendered unconscious within three
minutes, and results indicate that most kill traps currently in use fail the test (NAWAC
2000, in Warburton and Connor 2004).
Any planned mink control project should endeavour to gain public support through
educational means (eg: informing the public about the negative impacts of stoats on
native bird life). They should also be based around firm humane guidelines and legal
methods of disposing of the animals. Interestingly, the large majority of respondents
(96%) in a public survey responded that the least acceptable option (out of 13 stoat
control methods including not controlling stoats at all) was not controlling stoats at all.
This suggests that when weighing up the costs of damage done to the environment by
stoats against the costs (to stoats) of stoat control respondents preferred the options of
controlling stoats and were not prepared to allow stoats to remain uncontrolled in New
Zealand (Fitzgerald, Fitzgerald and Wilkinson 2005).
Under New Zealand legislation a non-target species must be killed as quickly and
humanely as possible. Animals must only be captured and killed in ways that fulfil legal
obligations under the Animal Welfare Act 1999 (New Zealand) (Ragg and Clapperton
2004). See www.maf.govt.nz/biosecurity/animal-welfare act to download a guide to the
Animal Welfare Act. For further legislation for pest control in New Zealand, Australia,
Europe and the United Kingdom please see Littin and Mellor (2005) (this document can
be downloaded from: https://www.oie.int/eng/publicat/rt/2402/PDF/littin767-782.pdf).
Furthermore, before any animal-research projects can proceed (eg: captive trials to
determine the toxicity of poisons, the efficacy of fertility control agents, and welfare
impacts of poisons and traps) in New Zealand they must receive approval from
institutional Animal Ethics Committees (AECs) (Warburton and Connor 2004). This is
usually done by assessing the ethical cost to the experimental animals (ie: pain and
suffering) in relation to the end benefits of the study (i.e. biodiversity conservation and
control of zoonoses) (Warburton and Connor 2004). However, it must be noted that this
process is often only achieved with vague benefits being provided (eg: to develop more
cost-effective protection of an endangered species), and weighed against equally vague
costs to welfare, as it is a difficult and subjective task to evaluate and quantify the costs
and benefits in these situations (Warburton and Connor 2004).
Further information
The Department of Conservation (New Zealand) DOC Technical Series has a wealth of
information on this topic. This can be accessed via a search on Mustela erminea at:
http://www.doc.govt.nz/templates/page.aspx?id=39160. In particular King (1994) and King,
O'Donnell and Phillipson (1994) have prepared a comprehensive guide to the monitoring
and control of mustelids on conservation lands. This guide is available in two parts (Part
1: Planning and Assessing an Operation and Part 2: Field and Workshop Guide), which
can be accessed at the aforementioned website or directly by using the websites in
reference list below.
For more details on the effectiveness of trapping stoats using different bait types, tunnel
designs, and trap positions please see Dilks et al. 1996, which can be accessed at:
http://www.rsnz.org/publish/nzjz/1996/109.php.
To access an international bibliographic database of stoat information please go to the
searchable, interactive Australian based website at: www.feral.org.au. Alternatively, to
access a simple reference list go to: http://bio.waikato.ac.nz/staff/bibliography.pdf.
For a discussion on the ethics of stoat and other animal control please see Littin and
Mellor (2005) Strategic Animal Welfare Issues: Ethical and Animal Welfare Issues Arising
From the Killing of Wildlife for Disease Control and Environmental Reasons. This may be
accessed at: https://www.oie.int/eng/publicat/rt/2402/PDF/littin767-782.pdf.
References
Clapperton, B.K. and Day, T.D. 2001. Cost-effectiveness of exclusion fencing for stoat and other pest
control compared with conventional control, Department of Conservation Science Internal Series 14.
Department of Conservation: Wellington. [Accessed 14 March 2007, from:
http://www.doc.govt.nz/templates/page.aspx?id=39160]
Clapperton, B.K., Robbins, L., Porter, R.E.R. and Tallentire, K. 2006. Testing the Attractiveness,
Palatability and Longevity of Stoat Lure and Bait Formulations, Department of Conservation Research and
Development Series 241. Department of Conservation: Wellington. [Accessed 14 March 2007, from:
http://www.doc.govt.nz/templates/page.aspx?id=39160]
Dilks, P.J., O'Donnell, C.F.J., Elliott, J.P. and Phillipson, S.M. 1996. The Effect of Bait Type, Tunnel
Design, and Trap Position on Stoat Control Operations for Conservation Management, New Zealand
Journal of Zoology 23: 295-306. [Accessed 20 March 2007, from:
http://www.rsnz.org/publish/nzjz/1996/109.php]
Eason, C.T and Wickstrom, M. 1997. Vertebrate Pesticide Toxicology Manual (Poisons): Information on
Poisons Used in New Zealand as Vertebrate Pesticides (2nd ed.), Department of Conservation Technical
Series 23. Department of Conservation: Wellington. [Accessed 18 March 2007, from:
http://www.doc.govt.nz/templates/page.aspx?id=39161]
Fitzgerald, G., Fitzgerald, N. and Wilkinson, R. 2005. Social Acceptability of Stoats and Stoat Control
Methods: A Survey of the New Zealand Public, Science for Conservation 253. [Accessed 18 March 2007,
from: http://www.doc.govt.nz/upload/documents/science-and-technical/sfc253.pdf]
Gillies, C. and Williams, D. Undated. Using Tracking Tunnels to Monitor Rodents and Mustelids.
Department of Conservation. Unpublished.
Hamilton, B. 2004. Using colour to increase stoat (Mustela erminea) trap catch, Department of
Conservation Science Internal Series 187. Department of Conservation: Wellington. [Accessed 14 March
2007, from: http://www.doc.govt.nz/templates/page.aspx?id=39160]
King, C.M. 1994. Monitoring and Control of Mustelids on Conservation Lands: Part 1: Planning and
Assessing an Operation, Department of Conservation Technical Series No. 3. Department of Conservation:
Wellington. [Accessed 18 March 2007, from: http://www.doc.govt.nz/upload/documents/science-andtechnical/docts03.pdf]
King, C.M., O'Donnell, C.F.J. and Phillipson, S.M. 1994. Monitoring and Control of Mustelids on
Conservation Lands: Part 2: Field and Workshop Guide, Department of Conservation Technical Series No.
3. Department of Conservation: Wellington. [Accessed 18 March 2007, from: http://publ.doc.govt.nz/dbtwwpd/exec/dbtwpcgi.exe?AC=GET_RECORD&XC=/dbtwwpd/exec/dbtwpcgi.exe&BU=http%3A%2F%2Fwww.doc.govt.nz%2Ftemplates%2Fsrpublicationsform.ht
m&TN=pubslive&SN=AUTO17094&SE=164&RN=2&MR=20&TR=0&TX=1000&ES=0&CS=1&XP=&
RF=scipubswebreport&EF=Basic+Record+Form&DF=Websitedisplay&RL=0&EL=1&DL=0&NP=3&ID
=&MF=searchbutton.ini&MQ=&TI=0&DT=&ST=0&IR=2887&NR=0&NB=0&SV=0&BG=0&FG=0000
00&QS=scipubswebquery]
Lawrence, B.L. and O’Donnell, C.F.J. 1999. Trap Spacing and Layout: Experiments in Stoat Control in the
Dart Valley, 1992-95, Science for Conservation 118. [Accessed 19 March 2007, from:
http://www.doc.govt.nz/upload/documents/science-and-technical/SFC118.pdf]
Littin, K.E. and Mellor, D.J. 2005. Strategic Animal Welfare Issues: Ethical and Animal Welfare Issues
Arising From the Killing of Wildlife for Disease Control and Environmental Reasons, Rev. sci. tech. Off.
int. Epiz. 24 (2): 767-782. [Accessed 18 March 2007, from:
https://www.oie.int/eng/publicat/rt/2402/PDF/littin767-782.pdf]
McDonald, R. A. and Harris, S. 2002. Population Biology of Stoats Mustela erminea and Weasels Mustela
nivalis on Game Estates in Great Britain, Journal of Applied Ecology 39: 793-805.
McDonald, R.A. and Lariviere, S. 2001. Diseases and Pathogens of Mustela spp., With Special Reference
to the Biological Control of Introduced Stoat Mustela erminea Populations in New Zealand, Journal of The
Royal Society of New Zealand 31 (4): 721-744. [Accessed 18 March 2007, from:
www.rsnz.org/publish/jrsnz/2001/38.pdf]
Ragg, J.R. and Clapperton, B.K. 2004. Ferret Control Manual. (Prepared for: Animal Health Board,
Wellington). [Accessed 18 March 2007, from: http://www.ahb.org.nz/NR/rdonlyres/D86FEEE4-FA9C4F1D-A6EC-6F519015D001/114/R80596FerretControlManual.pdf]
Robbins, L., Clapperton, B.K., Tallentire, K. and Porter, R.E.R. 2007. Testing the Attractiveness and
Palatability of Stoat Lures and Baits With Various Sensory Cues, Department of Conservation Research
and Development Series 265. Department of Conservation: Wellington. [Accessed 14 March 2007, from:
http://www.doc.govt.nz/templates/page.aspx?id=39160]
Spurr, E.B. O’Connor, A.T., Airey, A.T. and Kerr, J.H, 2002. FeraCol® for the Control of Stoats (Mustela
erminea), Department of Conservation Internal Series 61. Department of Conservation: Wellington.
[Accessed 20 March 2007, from: http://www.doc.govt.nz/upload/documents/science-andtechnical/DSIS61.pdf]
Smith, D. and Jamieson, I.G. 2003. Movement, Diet, and Relative Abundance of Stoats in an Alpine
Habitat, Department of Conservation Science Internal Series 107. Department of Conservation:
Wellington. [Accessed 20 March 2007, from: http://www.doc.govt.nz/upload/documents/science-andtechnical/DSIS107.pdf]
Warburton, B. and O’Connor, C. 2004. Research on Vertebrate Pesticides and Traps: Do Wild Animals
Benefit? In: Research on Animals for Animal Benefit, Fourth World Congress, ATLA (Alternatives to
Laboratory Animals) 32 (Supplement 1): 229–234. [Accessed 15 March 2007, from:
http://www.worldcongress.net/2002/proceedings/B6%20Warburton.pdf]