The eradication of muskrats and coypus from
Britain
L. M. GOSLING AND S. J. BAKER
C y p u Research I;ahoratory, Ministry of Agriculture, Fisheries and Food, Jupiler Road,
Norwich NRG GSP
Introduced vertebrates cati cause massive cnvironrncntal daniagc hut nwst a t t r m p t s to rrniovc fcrd
populations havr failed. 'I'his papcr discusses the rradication campaigns against feral muskrats,
Ondatra Zzbelhiczu, and coypus, M'oca.\lor coypus in Britain. Both specks were introduced in the 1920s
10 hr farmed for pelts and feral populations became rstablishcd following escapes. 'l'lrc risk of
environmental d a m a g r by muskrats was well known from Europe a nd ;in eradication campaign
started promptly in 1932 making use of overseas exprrtisc and a control strategy designed by pest
control specialists. 'l'hr campaign was brought to a successful conclusii~nin 1939 whcn a t lcast 4388
muskrats had h r r n killcd.
I n the 1930s, fc.w belirved that coypiis would cau. ignificant eiivironmcnt
trapping efforts were inadequatr. An early campaign achirved only limitrd s u
of the lack of biological information. T h e eradication cmnpaign which started in 1981, was based on
a long trrm study of population ccology. The effect of trapping and cold wcatlicr was quantified and
detailed population qiniulations were used to plan thc numbers ol' trappcrs, the time nccdcd for
eradication arid thus the likely cost of the campaign. An iiicciitive bonus scheme was dcsignrd to
ovrrcomr the problem that trappers would hr rcluctant to work themselves out o f a job. Trapper
deployment was plariiicd using capturc/trapping eKort ratios aiid progress was c ticckcd by Ministry
of Agriculture field stalf:
'l'hc muskrat campaigns su
d r d hrcausc trchrrical informatiorr to help plan thr work was
;t\ailahlc and brcaiisc action w
tkcn quickly. Wlicrc an introduced population is well cstxhlishcd,
a h with coypus in Britain, a cl05cly i n t r p t c c i programme iir
opulation rcology and
a well-plannrd control organi~ationmay he csscntial for S I I
KEY WORDS: -Muskrats
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coypus
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population ccology
rradication
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~~
Britain
CON'I'EN'I'S
Introduction .
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Background to the sprcirs .
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T h e introduction of muskrats and coypus 10 Britain.
Damage . . . . . . . . . . .
Perception of tlic prolilcm arid the difTcritig rcspoiises
Control strategies .
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Muskrats.
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coy]ius .
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'I'rapping tcchniques .
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Trapper motivation
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Conclusions .
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Acknowledgrmcnts
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References
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muskrats and coypus
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INTRODUCIION
'Ihe introduction of mammal spccics outside their native rangc can rcsult in
severe damage to agriculture an d the natural environment. Ma n y native species
39
00'24-4066/89/090039
+ 13 $03.00/0
0 1989 T h e Linneati
Society of London
40
L M. GOSLING AND S. J. BAKER
of plants and animals have been brought to extinction by introduced species and
this process continues. Most attempts to remove introduced species have failed, a
British example being the attempt to eradicate mink, Mustela uzson, which started
in 1965, employed nine trappers, and was abandoned in 1970 (Thompson,
1971).
This paper is about the eradication campaigns against muskrat, Ondatra
sibethicus (Warwick, 1934, 1940; Munro, 1935) and coypus, Myocastor coypus
(Gosling & Baker, 1987; Gosling, Baker & Clarke, 1988) in Britain. T h e muskrat
campaign was brought to a successfLi1 conclusion in the 1930s. Further checking
is needed before a final judgement can be made in the case of the recent
campaigns against coypus, but, at the time of writing, only two isolated coypus
have been detected over the past 21 months. I t seems unlikely that a breeding
population remains and trapping ceased in ,January 1989. Here we outline the
reasons for thcse successes so that, hopcfully, the lessons can be applied
elsewhere.
BACKGROUND ‘1‘0 THE SPLCIES
Muskrats are myomorph rodents which reach up to about 1.8 kg in weight
(Walker, 1983). Many muskrats brought to Britain came from Canada
(Warwick, 1934; Munro, 1931). Their breeding is seasonal and in Britain they
had two or rarely three litters between April and October (Warwick, 1940).
Gestation is 25-30 days (Walker, 1983) and litters average between five and
seven young (Danell, 1978; Clay & Clark, 1985).
Coypus are hystricomorph rodents, native to South America which weigh
6 7 kg when fully grown; their biology is described elsewhere (Newson, 1966;
Gosling, 1986; Gosling & Baker, in press). Coypus are poorly adapted to freezing
conditions (Newson, 1966; Gosling, 1981) and, in Britain, would probably have
a slower rate of population increase than muskrats, particularly in years
following cold winters.
Both species are semi-aquatic and swim from daytime resting sites in nests and
burrows to ferding areas in or near water.
T H E INTRODUCTION OF MUSKRAI S AND COYPUS TO BRITAIN
Muskrats and coypus are farmed for their pelts and many have been exported
from their native ranges for this purpose (Gosling & Skinner, 1984). They were
imported to Britain during the late 1920s (Lever, 1985). Over 87 muskrat farms
were quickly established throughout Britain although most were small
(Warwick, 1934). Enclosures were often inadequate and escapes were common.
All muskrat farming ended by 1933. Over 50 coypu farms were established,
mostly in the south and east of England. Nearly all had closed by 1939 but by
this time many had escaped (Laurie, 1946).
It is sometimes overlooked how difficult it is for animals to colonize new areas.
Apart from any novel hazards, the animals may be unused to living in the wild
and may simply escape without potential mates. The success of furbearers in
invading new habitats may be because they sometimes escape in sufficient
numbers to overcome these problems. Whatever the reasons, separate
ERADICATION OF MUSKRATS AND COYPUS
41
populations of muskrats became established in the Severn valley in Shropshire,
in a central area of Scotland and in two smaller areas in Sussex and Surrey.
Accurate estimates of the muskrat populations are not available but the
numbers killed give some impression. I n fact these numbers are only those killed
in the official trapping campaigns: for example, the Scottish population started
from escapes in 1927 and at least 140 animals were killed before the campaigns
started in 1932 (Munro, 1934; Lever, 1985). The total killed in Scotland was at
least 1108. At least 3052 muskrats were accounted for in Shropshire (Fig. 1) and
a further 228 were killed in Sussex and Surrey. T h e total caught from all four
sites was at least 4388 (Warwick, 1934, 1940).
One group of coypus became established near Slough, remained a t a low level
and disappeared without any known control in 1956 (Norris, 1967b). A second
group probably originated from three farms near Norwich, close to the Rivers
Yare and Wensum (Laurie, 1946). The best known escape was from a farm at
East Carlton in 1937 (Ellis, 1960). T h e East Anglian wetlands have many
similarities to the coypus’ native swamps in South America and coypus soon
increased and spread into adjoining rivers. At their peak in the 1950s most were
in Norfolk, Suffolk and Essex but significant numbers had also spread to
neighbouring counties (Davis, 1963; Norris, 1967b).
The size of the coypu population is known in detail after 1962 (Gosling, Watt
& Baker, 1981, and see Fig. 5) but earlier information is anecdotal. The
population started in about 1937 and grew progessively with the first complaints
about damage in 1943 (Laurie, 1946). There were major checks in the severe
winters of 1946/47 and 1962/63. In the late 1950s, there was a dramatic eruption
in numbers: Rabbit Clearance Societies were grant-aided to control coypus and
local drainage organizations increased their efforts to limit the increasing
damage. About 100 000 coypus were killed in 1961-62 without greatly affecting
the population (Norris, 1963). Centrally-organized control started in 1962 and
continued at various levels until the start of the eradication campaign in 1981.
Maximum numbers were once believed to be 200 000 in the late 1950s (Norris,
1967b) but this may have been an overestimate.
DAMAGE
Coypus and muskrats are generalist herbivores which damage a wide variety
of native plants and crops in their introduced ranges. Coypus often destroy
monocotyledonous plants by selecting basal meristems (Gosling, 1974) and large
areas of reedswamp were eliminated during the late 1950s (Ellis, 1963; Boorman
& Fuller, 1981). Coypus also favour particular species and some, including
Butomus urnbellatus, the flowering rush, and Cicuta virosa, cowbane, became
extremely rare (Ellis, 1963). Muskrats in North America also cause extensive
damage to marshland vegetation when at high population densities (Errington,
1963). Fortunately, their numbers in Britain did not reach the levels at which
large scale damage to native plants would have occurred.
Both species also damage a variety of crops: sugar beet are a favourite for
coypus but they also eat cereals, brassicas and other root crops (Norris, 1967b;
Anon., 1978). Muskrats did not cause significant damage to crops in Britain
(Warwick, 1940).
42
L. M ,GOSL.ING AND S. J . BAKER
The most important damage in economic terms is caused by burrowing. In
the Netherlands where 289 116 muskrats were trapped during 1987 alone
(Anon., 1988) there is extensive damage to the land drainage system. Damage
through burrowing was also recorded to the banks of the River Scvern in the
1930s (Warwick, 1940). The cost of repair in the Netherlands and the risk of
increased damage are so great that a current annual cxpcnditure ofseven million
pounds on control is considered cost effective (R. van Oostenbruggc, personal
communication). Coypus dig extensive burrow systems into the hanks of ditches
and rivers which disrupted drainage systems and posed the risk of flooding in
low-lying East Anglia (Cotton, 1963).
PERCEPTION O F T H E PROBLEM AND 'I'HE: UIE'E'EKEST RESPONSES TO MUSKKAI'S AND
COYPUS
The costs of future damage, both in economic terms and the natural
environment, cannot always he assessed at the early stages of an introduction.
This affects whether or not prompt action is taken. Fortunately, it was already
known from experience in Europe that muskrats could cause serious damage in
Britain and this information was used by staff of the British Museum (Natural
History), notably the zoologist M . A. C. Hinton, to persuadc the Ministry of
Agriculture and the Treasury that money spent on eradicating muskrat would
be worthwhile (Sheail, 1988).
These initiatives also led to the Destructive Imported Animals Act of 1932
which allows control over the importation and keeping of named animals.
Initially muskrats were only allowed to be kept under licence and in 1933 all
keeping was prohibited. By this stage stringent keeping requirements had
reduced the holdings to six (five in England and one in Scotland) and
compensation was paid to close these down. The act also authorized the Ministry
of Agriculture to carry out the eradication campaign.
Although the coypu population was growing steadily at the same time, coypus
were only added to the list of animals proscribed under the Act in 1962. There
are a number of reasons for this. 'l'he first was that relatively little was known
about the biology ofcoypus and their potential for damage in the 1930s. Coypus
also have a lower potential rate of increase than muskrats, particularly over cold
winters, and SO early events were no so alarming. The advice from Germany,
where coypus had also been introduced, was that coypus would not cause
problems (Sheail, 1988). Although true in Germany where the cold continental
climate keeps coypus at a low level, it is not the case in Brtitain where winters are
milder. Coypus were also believed to be easy to catch if they escaped (CarillWorsley, 1932) and Hinton commented that they were unlikely to become a
serious pest (Sheail, 1988).
As a result, although there were some warnings about the potential dangers
(Stearn, 1981), little was done to prevent the establishment of coypus. Some
trapping was carried out by trappers employed by the Norfolk War Agricultural
Executive Committcc and 193 animals were caught between 1943 and 1945
(Laurie, 1946). But this trapping was localized and it was not continued. After
the cold winter of 1946/47 when numbers were greatly reduced there must have
seemed even less need to do anything.
ERADICAI‘ION OF MUSKKATS AND COYPUS
43
CONI’K<)L STRATEGIES
MuskratJ
The muskrat campaign in Shropshire was planned by Hinton and a Ministry
of Agriculture pest control specialist, E. C. Read (Public Record Office, MAF
44/14). Fewer details are available from other areas but presumably the
experience from Shropshire was put to use. Here, an oblong area was defined
using the locations of the outermost known muskrats in each area and divided
into squares each of ten square miles. A trapper was deployed to each of these
squares to survey and trap. This intensity of trapping appears to have been
decided on the basis of common sense estimates of the amount of ground one
man could cover. Motorized transport was very limited: one van was available
in Shropshire but most trappers either bicycled or walked to work.
The initial area trapped was just over 300 square miles (see Fig. 1 ) . This was
enlarged by 100 square miles in 1933 and later enlarged again as outlying
muskrats were found. However, the maximum number of trappers was 39 and so
presumably trappers worked over larger areas at later stages of the exercise.
Some men became specialized as ‘searchers’ to look for outlying muskrats. I t is
also stated in the historical documents (Public Record Office, MAF 44/14) that
effort should be progressively concentrated along rivers where the population
was most dense, as the outlying animals were cleared. How far this intention was
carried out is not know.
After early peaks of captures, the numbers of muskrats declined steadily to
zero (Fig. 2). T h e last animals in Shropshire, Sussex and Surrey were caught in
1935, and the last in Scotland in 1937 (Warwick, 1934, 1940). T h e last muskrat
in England, possibly an emigrant from the Shropshire population, was caught in
Cheshire, in 1936.
Number killed per
e
m
Figure 1. The distritiution ol“ muskrats caught in 1932 and 1933 in the trapping campaign in
Shropshire. Aftrr Warwick (1940).
I,. M. GOSLING AND S. J. BARER
44
1932
1933
-Trappers
1934
1935
I936
1937
1938
.*-***. Muskrats k i l l e d
Figure 2. The number of trappers employrd during the campaigns against muskrats in Shropshirc
and Scotland and the riunibrr of' muskrats caught.
As numbers declined there was financial pressure to reduce the trappers. Men
were gradually dismissed but with a sufficient lag that there was some effort in
the later years of the campaign when muskrat numbers were low (Fig. 2). In
Scotland some trapping was maintained until March 1938 even though only two
muskrats were killed in the last 28 months of the campaign.
Cypus
As damage by coypus increased alarmingly in the late 1950s there were
widespread calls for official action. Two initiatives were taken by the Ministry of
Agriculture, Fisheries and Food (MAFF), both in 1962: the first was to establish
the Coypu Reserarch Laboratory in Norwich and the second to launch a
trapping campaign against coypus. The aim of the campaign was to reduce
coypus and confine the remainder to the Norfolk Broads (Norris, 1967b).
ERADICATION OF MUSKRATS A N D COYPUS
15
By necessity, the control strategy adopted in this initial operation was
organized in advance of any results from the laboratory. The area containing
most coypus (nearly all of Norfolk plus north Suffolk, see Davis, 1968) was
divided into nine sectors which were trapped successively by up to 14 specially
employed trappers starting a t the outside and working north-east towards the
Broads. A large amonnt of trapping was also carried out ahead of the campaign
by Rabbit Clearance Societies and landowners. Behind the sector organization,
permanent MAFF staff attempted to clear what were regarded as outlying
colonies (Norris, 196713).
I t is easy to be wise after the event and in retrospect flaws are evident in this
strategy, notably that the main trapper force spent too much time in clearing
low density areas rather than attempting to maximize capture rates. While the
effect of immigration into cleared areas was considered it was not given sufficient
weight and an increasing proportion of time was devoted to controlling
reinfestation of areas which had been trapped previously.
Events were also complicated by the winter of 1962/63, the coldest for over
200 years, when about 90% of the coypu population perished. At the end of the
campaign in 1965 the main objectives had been achieved but in the absence of
basic demographic knowledge it was not clear to what extent cold weather or
trapping were responsible. Perhaps the main achievement was to keep numbers
down to the low levels caused by the cold winter. But in the absence of an
understanding of the relationship between trapping effort and population
response the trappers were reduced to five men in 1965. This force could not
prevent an eruption in numbers when a run of mild winters occurred in the early
1970s (Gosling et al., 1981).
I n contrast, the 1981 eradication campaign was designed using the results of a
long term investigation of coypu population ecology. Ovcr 30 000 coypus from
the continuing trapping operation were dissected to obtain information about
reproductive biology and other data needed to understand why coypu numbers
varied. A priority was to estimate population size and, since most adults are
eventually killed by trapping, this could be done by reconstructing the numbers
alive, each month in the past, from the numbers and ages of the animals caught
in the control operation (Gosling et al., 1981). It was then possible to quantify
the short term effect of trapping on the adult sector of the population and assess
the relative importance of cold weather as a limiting factor. Except in
exceptionally severe winters, cold weather has its main effect through reduced
breeding success and juvenile survival. Trapping intensity proved to be a more
important factor in explaining change between years (Table 1) and, together,
trapping and winter severity explained 82% of the variation in the change in
coypu numbers. By the late 1970s enough was known to provide a n analytical
background for attempts to build simulation models of the population (Gosling
& Baker, 1987).
These simulations were used to assess the effect of employing different
numbers of trappers on the response of the population under various climatic
circumstances. A range of simulations (Fig. 3 ) were considered in the late 1970s
when an independent committee, the Coypu Strategy Group, took a fresh look
at long term policy for coypu control (Anon., 1978). T h e option recommended
and subsequently accepted by the MAFF was an attempt to eradicate coypus
using 24 trappers. Taking into account reasonable expectation of improved
L. M. COSLIN(: A N D S. J . BAKER
46
TABLE1. Multiple regression analysis of the effect of trapping
intensity and winter severity on the change in the mean number
of adult coypus alive in successive years. The number of adult
coypus was obtained from a monthly reconstruction of'the population (Gosling et al., 1981) averaged for cach year between 1970
and 1987. Wintcr scvcrity is cxprcssed using a n index which weights
arid accumulates runs of frerzing days cach winter (Gosling, 19811;
trapping intciisity is the number of trap-nights in year y whare the
change in coypus numbers is calculated between y and y + 1
Indcpendcnt variable
Beta
t value
P
Trappiug intensity
Wintcr scvcrity
-0.73
- 0.26
- 6.06
<0.001
0.03
Coefficient of dctrrmination
=
- 2.41
0.82, F = 38.6; d.f. 2 , 14
trapping techniques, and an average number of cold winters, it was decided to
attempt eradication within ten years.
The existing Coypu Control Organization was reconstituted and the
eradication campaign started in 1981. Biologists from the Coypu Research
Laboratory gavc technical guidance throughout the campaign. An example is
the scheme used to deploy trapping effort (Fig. 4). Trapper deployment was
more flexiblc than in thc muskrat campaign because cach trapper had a car.
Recommendations were made every three months using past capture:trapping
4
= Cold winter
3
v
0
c
0
...........
:-.
.....
..............
24 trappers
....
..............
.............. .................
2
3
4
5
24 trappers
34 trappers
6
Year
Figure 3. Simulations of adult female coypu numbers in relation to various trapping intensitirs.
'l'hese simulations are some ofthosc considered as options by the Coypu Strategy Croup in 1977 and
docuniriitcd in their 1978 rcport. Iimited inforniation about the efftw of cold weather was available
in 1977 and the simulation with 24 trappers and occasional cold winters simply replicates the rffrct
of tlic 1975/76 winter. When further data were collected in subsequent years i t heramr possihle to
explore the effcct of cold weatlicr in more detail (Gosling et al., 1983).
EKADICAI'ION OF MIJSKKXTS AND COYPUS
47
PI
P2
Figure 4. 'l'hc distribution (if coypus caught during the 1981-1'189 er;idic,;rtioii c.anip;iign ;ind tl1c
regions used Ihr stratrgic drpluyrnrnt ol ' t rappi i i ~~lI'01.t.'l'he circles o n (lie m a p rcprescrit < O , I , 0.I
1 .O aild > I .O",, of thc total number caught (ri = 34 822). Effort ~ v a sdcploycd i n proportion ((1
weightrd capturc:trapping clli)rt ratios. rllthougli some trapping cviis c.;lri-ird out I Iirouglioui the
area the initial aim, using strongly wcightcd ratios, with to C U I I C C I I W ' I ~ ~c l h r t in tlic high clcrisiiy
.
regions, C1 and C2, 10 maximize rnorlnlicy and ininimizc cmigratiori i o pcriplicl.al ~ ( x-4s~thc.
'core' arras wcrr rrducrd, the weighting h c t o r w w rcduccd t o deploy trapping cffiiri inore c\~cnly
arid thus p a y relatively more attention ((I t t i c pcripticr) .
effort ratios in eight strategic regions (Fig. 4) and available effort was
apportioned in proportion to the magnitude of the ratio in each region. This
ratio was weighted to different extents so that effort could be concentrated on
high density areas early in the campaign and deployed more widely later on.
The laboratory also monitored progress by field checks, by reconstructing the
population (Fig. 5) and using simulation techniques to detect and analyse trends
(Gosling & Baker, 1987). Numbers were reduced from around 6000 adults in
1981 to near-zero in 1987. T h e campaign was helped by an above average
number of cold winters. However, cold weather by itself would never eradicate
all coypus in Britain, as shown in the exceptional winter of 1962/63. The main
effect of cold weather in the campaign was to lower recruitment to the adult
sector of the population by reducing breeding success and juvenile survival
(Gosling & Baker, 1987) thus allowing trapping to make a relatively large
impact on adult numbers.
TRAPPING TECHNIQUES
The main technique used in the muskrat campaign was leg-hold trapping
using smooth-jawed traps, possibly following the Canadian experience of the
field manager of the Shropshire area. The traps had long chains so that trapped
animals could get to deep water and drown. Where this did not happen some
animals escaped with severed legs. 'There was also a large toll of non-target
L. M. GOSLING AND S. J. BAKER
...
7 0 ‘ 7 1 1 7 2 1 7 3 1 7 4 1 7 5 ~ 7 6 ‘ 7 7 ~ 7 8 ~ 789, 1~8802i ‘ 8 3 ’ 8.....
$ ~ 8 5 ~ 8 6 ~ 8 7 ’ 8
Year
......
coypus
-
Vigurc 5. Rccoiistructed numbers of adult coypus and trapping intensity during 1970-1988. ’l‘lic risr
in the early 1970s was due to a rnii of mild wintrrs with inadrquatr trapping. ‘l‘hc eradication
i.arnpaign starred oficially in 1981 although the trapping h r c r had hrrn built up ovrr tlir prcvir)us
wintcr. T h c liighcr tlian avcragc number of cold winters probably accelcratcd tlrc campaign bul
cold wiritcrs by tlicrnsclves would never remove coypus from Britain. ‘Ihc population r c c ~ r i s t r u ~ t i ~ i n
technique is documrntrd b y Gosling el al. (1981).
captures with over 6500 mammals and birds killed in Scotland alone (Munro,
1935).
Both campaigns against coypus used cage trapping (Norris, 1967a). Each trap
was inspected daily and any coypus shot. This technique has the advantage that
non-target animals can be released unharmed. Apart from being ethically
desirable, this also made it possible to get the cooperation of all landowners,
including those with conservation and game interests. Improvements to trapping
techniques were introduced by the Coypu Research Laboratory, including the
use of traps on baited rafts. Experiments showed these were at least 50% more
effective than traps set on land and following this work over 600 were deployed.
Non-target captures were also significantly reduced (Baker & Clarke, 1988).
1RAI’I’ER M O I LVAI’ION
Why should trappers try to succeed in an eradication exercise when in doing
so they lose their jobs? This problem is often raised but, to our knowledge, the
attempt to overcome it in the coypu eradication campaign is the first time it has
been tackled in a pest control operation. The scheme devised was to restrict the
funding to a maximum of ten years and promise the trappers a bonus of u p to
three times their annual salaries if they succeeded in eradication. The scheme
was designed so that after six years the bonus would gradually decline, thus
encouraging an early end to the campaign. Most trappers worked hard to
E R A D I C A I I O N OF MUSKRATS AND COYPUS
49
achieve the maximum bonus and we believe that this incentive was an essential
element in the campaign.
If the bonus scheme was essential in coypu eradication then why did the
campaigns against muskrats succeed, even when the numbers of trappers were
reduced as the campaign proceeded? T h e reasons may be partly technical and
partly sociological. The muskrat-trapping technique was designed so that
animals were killed as they were caught and while this does not seem to have
worked universally it would have limited the opportunity for trappers to control
events. Secondly, societal values in the 1930s were different and perhaps people
were more ready to follow instructions than today, even when it meant their
eventual dismissal.
Bounties were paid for both muskrats (Sheail, 1988) and coypus a t various
times and pelts were also sold for profit. It is sometimes believed that such
rewards encourage people to reduce pest numbers and this may be true under
restricted circumstances. More often these practices will encourage husbandry of
the animal to ensure a continuing income. Fortunately, bounties for muskrats
were discontinued before the start of the official trapping campaigns and
although pelts were sold during the campaigns, the profit was used to offset costs,
not to reward the trappers. T h e sale of coypu pelts by trappers was forbidden
during the coypu eradication campaign hut, in any case, demand was low at this
time and the potential rewards small in relation to the possible eradication
bonus.
CONCI.USTONS
What are the lessons of these two campaigns for other attempts to remove
introduced species? It must be borne in mind in considering these that there is a
justifiable reluctance on the part of those who must finance any operation to take
action unless ( 1 ) they believe there is a problem, (2) they think it can be solved
and ( 3 ) they know, within limits, how much it will cost. The muskrat campaign
was undertaken because important elements of this information were available
from experience in Europe and Canada. However, this might not have been
sufficient without the skilled technical advocacy of M . A. C. Hinton. The
campaigns were organized using common sense principles and although there
was little technical input into the field exercise, there was the great advantage
that action was taken quickly. Experience in Europe shows how remote the
chances of success would have been if the populations had been allowed to
spread more widely,
The coypu eradication campaign would simply not havc becn undcrtaken
without detailed technical assessments of the effort and costs required and the
likely chances of success. These assessments were only achieved by a long term
study of population ecology, targeted to a particular control application. This
study included operational experience as well as applied ecology and it is
significant that the arguments for such practical details as the inccntivc bonus
scheme came from biologists.
One reason that the eradication of muskrats and coypus could be considered
was that their populations were confined to reasonably small areas with no
immigration. However, even in other situations where eradication is not possible,
for example where large scale immigration from a neighbouring country
SO
L. M . (:()SLING AND S. J . BAKER
continually replenishes a controlled population, the principles which emerge in
considering the removal of muskrats and coypus can be applied. Indeed, these
principles may he applicable to the sensible management of any population of
vertebrates. Most important is the need for applied population ecology, so that
the role of various factors, including control techniques in limiting the subject
population can be evaluated. Next there must be a target population density
over a defined area which can be independently monitored. This target could tic
eradication or a density low enough t o preclude environmental daniage. In tlie
coypu eradication exercise, the control organization wits centralizcd ~ ~ ~ X L I t Sh vO
aim was to eradicate a single population but a coordinated system of' local
organizations might sometimes be more appropriate. Next, the peoplc carrying
out the control in the field must be rewarded for achieving their objective arid
not for failing to do so (as with bounties). However, where incentive schemes arc
used, results need to be independently monitorcd. In the campaign against
coypus, estimates of trapping effort, population trends and the results of field
checks were passed to the control organization arid this helped both dircctly and
i n stimulating the efforts oT tlie trappers. 'l'his sort of information is also needed
by the contributing organizations to cvaluatr tlie results of their finaricial
investment at each stage of the exercise.
This sort of interaction between applied biologists, policy makers, funding
organizations and a well-coordinated control operation has potential for wide
application in any extcnsive pest control operation. I t may be essential for the
removal of a well-established introduced mammal.
ACKNOM'LEnCEMEN1'S
The Coypu Chntrol Organization supplicd information arid material Ihr post
mortem examination and the Public Record Oflice, the Scottish Record Office
and colleagues in the department oTAgricultur-c and E'ishcrir:s provided accvss to
files on the muskrat campaign. Commcnts by T. Warwick arid D. 6. Drummond
improved an carlicr draft.
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