See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/227800788 The eradication of muskrats and coypu from Britain Article in Biological Journal of the Linnean Society · August 1989 DOI: 10.1111/j.1095-8312.1989.tb01561.x CITATIONS 193 READS 3,883 2 authors , including: Leonard Morris Gosling Newcastle University 76 PUBLICATIONS 4,335 CITATIONS SEE PROFILE All content following this page was uploaded by Leonard Morris Gosling on 09 October 2017. The user has requested enhancement of the downloaded file. B i o t o g i c a l . / o u r n a l o J t h e L i n n e a n S o c i e t v ( 1 9 8 9 ) , 3 8 . ' 3 9 5 1 . \ \ ' i t h 5 f i g t r r c s The eradication of rnuskrats and coypus frorn Britain L. M. GOSLTNG AND S..1. BAKER OolpuResearch [,aboratory, Ministry of Agriculture, Fisheries and Food,Jultiter Road, JtforwichlVR66SP Introduced vertcbrates can cause massive environmcntal damagr: but most att('mpts to rcrnovc lcral p o p u l a t i c l n s h a v c f a i l c d . ' l ' h i s p a p c r d i s c u s s c s t h c c r a d i c a t i o n c a m p a i s n s a g a i n s t f t ' r a l m u s k r a t s , Ondatra lihethicus, and cclypus, Mytcastnr colltus ttt Britain. Both spccics rvcrc introduced in thc 1920s to bc larmcd for pclts and leral populations became cstablisht'd follorving cscapcs. 'l'hc risk of e n v i r o n m e n t a l d a m a g c b y m u s k r a t s w a s r v c l l k n o w n l i o m F ) u r o p c a n d e r n c r a d i r : a t i t , n t ' u m p a i q n s t a r t c d p r o m p t l y i n 1 9 3 2 m a k i n g u s c o f o v c r s c a s c x p c r t i s c a n d z r c o n t r o l s t r a t c g , v d c s i s n c d b v p c s t c o n t r o l s p e c i a l i s t s . ' l ' h e c a m p a i s n w a s b r o u g h t t o a s u c c c s s f r r l c o n c l u s i o n i n 1 9 3 9 w h e n l r t l c a s t ' l 3 8 f l muskrats had becn killed. I n t h e 1 9 3 0 s , l e w b e l i e v e d t h a t c o v p u s w o u l d c a u s c s i g n i f i c a n t c n v i r o n m c n t a l d a m a s e r a n d c a r l v trapping ellr,rrts were inadcquatc. An carl,v campaisn achievccl onlr. limitt'd su('('css1 partly bct':rusc o f t h c l a c k o f b i o l o g i r : a l i n f o r m a t i o n . ' l ' h e c r a d i c a t i o n c a m p a i g n r v h i c h s t a r t e d i n l 9 8 l , r v a s b a s c d o r r a k;ng tcrm study ol'population ecolclgy. 'l'hc cffcct of trapping ancl cold lvcatht'r rvas quantificd and dct:rilt:d population simulations wcrc uscd to plan tht' numbcrs o{- truppcrs, tht' timc nccdcd lirr eradication and thus thc likcly cost of thc t'ampaign. An incentive bclnus si'hcme rvas dcsignr:d t 1 > i r r e c { J i r r t . ' ] - h e c i l t ' l c s o n t h t ' m : r l ) r ( ' J ) r c s ( n l < 0 . 1 . 0 . 1 1 . 0 a n c l > 1 . 0 " , , < r l t h t ' t ( ) t i t l n u n r l ) < ' r t ' a u g h t ( n : I i 4 t i 2 2 1 . I . , f l i r r t n i r s c l t ' p l o r < ' c l i n l r r o p r ) r u ( ) n r ( ) " v c i e h t t ' d ( ' i I J ) t u r c : t r i l p p i n g t ' f l i r r t r i i t i ( ) s . A l t h o r - r c h s ( ) r n ( ' t r a l ) l ) i r r s u . a s c a r r i t ' c l o r r t t l r r o r i g l r o r r t t h t ' a r ( ' a t h ( ' i n i t i a l a i m . u s i n g s t r o n g l r u e i g h t c c l r i i t i t . r s . u ' l r s t ( ) ( ( ) n ( ( ' n t r i r t ( ' c l l i r l t i n t h t l r i c h c l r ' l r s i t t I ' t ' q - i o t t s ' ( l l a r r c l ( 1 2 , t o t n a x i t n i z e n r o l t a l i t v a n c l r r r i n i n r i z t ' t ' r r r i 1 1 r ' u t i r ) n t ( ) l ) ( , r ' i l ) l l < ' r ' : . r l i r n . ; 1 s . , \ s t l r t ' ' ( ' o r e ' a r e a s r v e r e r e c l u t ' t ' d , t h c r v c i q h t i n g l l t c t r l r w a s r c c l u < ' r ' c l t o d c p l o r t r a p p i l l q < ' l i i r r t r n r t r t ' < ' r . r ' 1 l y a r r r l t h u s l t a v r c l a t i v c l v r n < t r t 'a t t c n t i o n t < t t h c p c r i p h c r r ' . effbrt ratios in eight stratesic resions (Fig. a) and available eflorr was a p p o r t i o n e d i n p r o p o r t i o n t o t h e m a c n i t ude of the ratio in each resion. This ratio was weishted to different extents so that effort could bc conccntratcd on h i g h d e n s i t y a r e a s e a r l y i n t h e c a m p a i g n arld deployed more widely larer on. The laboratory also monitored progress by field checks, by reconstructine the p o p u l a t i o n ( F i g . 5 ) a n d u s i n s s i m u l a t i o n t echniquesto detect and analyse trencls ( G o s l i n g & B a k e r , l 9 B 7 ) . N u m b e r s w e r e reduced from around 6000 adults in l 9 8 l t o n e a r - z e r o i n 1 9 8 7 . T ' h e c a m p a ign was helped by an above averase n u m b e r o f c o l d w i n t e r s . H o w e v e r , , c o l d weather by itself would never eradicatc a l l c o y p u s i n B r i t a i n , a s s h o w n i n t h e e x ceptional winter of 1962/63. The main e f f e c t o f c o l d w e a t h e r i n t h e c a m p a i q n was to lower recruitment to the adult s e c t o r o f t h e p o p u l a t i o n b y r e d u c i n g b reedins succcssand juvcnilc survival ( G o s l i n g & Ba k e r , l 9 B 7 ) t h u s a l l o w i n s trapping to make a relatively large i m " p a c t o n a d u l t n u m b e r s . TRAPPING TECHNIqUE,S 'I'he main technique used in the muskrat campaisn was leg-hold trapping using smooth-jawed traps, possibly followine the Canadian experience of the field manager of the Shropshire area. The traps had long chains so rhat rrapped a n i m a l s c o u l d g e t t o d e e p w a t e r a n d d r o wn. Where this did not happen io-. animals escaped with severed legs. There was also a large toll of non-target +7 a a o o o f o o o O O a a a a a a a a a o o a o o o a o o a o 1 a a a o o o o o o r f a a o o o a o o o a o o a a o o o o ? o o o ) ,. O O oo o o o o o o o o o o a a o f O o O a a a o a o o 4B L . N ' I .G O S L I N G A N D S . I . B A K E R 3 0 t o 25 2 a o (J () I 15 a -c I c I o o a) o A n l o o- > o (J = a A o o E f, z - a 8 4 8 8 8 7 8 6 8 5 8 3 8 2 8 I 8 0 7 B 7 7 76 7 5 74 7 3 7 2 7 l 70 Yeor . . . . . . C o y p u T r o p - n r g h t s I C o t O * , n r " r . l i g L l r e 5 . R e c o u s t n r c t c t l r t u m b t - r s o f a d u l t c ( ) \ ' l ) u si l n d t r a p p i r ) g i n t e n s i t v c l u r i l q 1 9 7 ( ) l 9 8 B . ' l ' h c r i s c i n t h c c a l l v l 9 T 0 s w a s d u c t o a r u n o 1 r r r i l d n ' i n t c r s r v i t h i n a d e c l u a t c t r a p p i n s . ' l h c c r a d i ( ' a t i o l l t : a m p a i { n s t a r t e d o f l i c i a l l v i n l 9 8 l a l t h o u g h t h e t r a p p i n s l i r r c e h a d b c c n b u i l t l l p o v e r t h c p r c v i c ' r u s r,r'itrtcr. 'I'ht' hieircr than avt'rase rtut.nbcr o{ cold u'intcrs probaLrlv accclcrat('d thc campaign lrtrt c o l d r v i t r t c r s l r v t h c m s c l r c s u ' o u l d r ] c v c r r c m o v c c o v p u s l i o m B r i t a i n . ' l ' h t ' p r i p u l a t i o n r t ' t o n s t r u t t i o r r t c c l r r i i q u e i s d o c u m e n t e d b r G o s l i : n ge l a l . i l 9 8 l l . c a p t u r e s w i t h o v e r 6 5 0 0 m a m m a l s and birds killed in Scotland alone (Nlunro, l e 3 s ) . B o t h ca m p a i q n s a g a i n s t c o y p u s u s ed cage trapping (Norris, 1967a). Each trap w a s i l r s pe c t e dd a i l y a n d a n y c o y p u s shot. This technique has the advantaqe that non-target animals can be released unharmed. Apart fronr being ethically desirable, this also made it possible to get the cooperation of all landowners, i n c l u d i n g t h o s e w i t h c o n s e r v a t i o na n d game interests.Improvements to trappins t e c h n i q ue s w e r e i n t r o d u c e d b y t h e Co,vpu Research Laboratory, including the u s e o f t r a p s o n b a i t e d r a f i s . E x p e r i ments showed these were at least 50il; more effective than traps set on land and fbllowing this work over 600 were deployed. N o n - t a r s e t c a p t u r e s w e r e a l s o s i g n i ficantly reduced (Baker & Clarke, l9BB). 'I'R.{PPI.]R }I O'f I\'A1'I ON Why should trappers try to succeed in an eradication exercise when in doine so they lose their jobs? l'his problem is often raised but, to our knowledge , the a t t e m p t t o o \ , e r c o m ei t i n t h e c o y p u eradication campaign is the first time it has b e e n t a c k l e d i n a p e s t c o n t r o l o p e r a tion. The scheme devised \ /as to restrict the funding to a maximum of ten years and pron-risethe trappers a bonus of up to t h r e e t i m e s t h e i r a n n u a l s a l a r i e s i f they succeededin eradication. The scheme was designed so that after six years the bonus would gradually decline, thus encourasins an early end to the campaign. Most trappers worked hard to E , R A D I C A ' I ' I O N O I M U S K R A ' I ' S A N D C O Y P U S + 9 achieve the maximum bonus and we believe that this incentive was an essential ele m e n t i n t h e c a m p a i g n . I f t h e b o n u s s c h e m e w a s e s s e n t i a l i n c oypu eradication then why did the campaigns against muskrats succeed, even when the numbers of trappers were reduced as the campaign proceeded? The reasons may be partly technical and pa r t l y s o c i o l o e i c a l . T h e m u s k r a t - t r a p p i n g 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 ev e n t u a l d i s m i s s a l . B o u n t i e s w e r e p a i d f o r b o t h m u s k r a t s ( Sheail, 19BB) and coypus at various times and pelts were also sold lor 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 encourase husbandry of the a n i m a l t o e n s u r e a c o n t i n u i n g i n c o m e . Fortunately, bounties for muskrats were discontinued before the start of the official trapping campaigns and although pelts were sold durine the campaigns, the profit was used to offset costs, not to reward the trappers. The sale of coypu pelts by trappers was lorbidden du r i n g t h e c o y p u e r a d i c a t i o n c a m p a i g n b u t , in any case,demand was low at this time and the potential rewards small in relation to the possible eradication bo n u s . C O N C L U S I O N S What are the lessonsof these two campaigns lor other attempts to remove introduced species? It must be borne in mind in considerins these that there is a justifiable reluctance on the part of those who must finance any operation to take ac t i o n u n l e s s ( l ) t h e y b e l i e v e t h e r e i s a p r o blem, (2) they think it can be solved an d ( 3 ) t h e y k n o w , w i t h i n l i m i t s , h o w m u c h it will cost. The muskrat campaien wa s u n d e r t a k e n b e c a u s ei m p o r t a n t e l e m e nts of this information were available from experience in Europe and Canada. However, this might not have been su f f i c i e n t w i t h o u t t h e s k i l l e d t e c h n i c a l a dvocacy of M. A. C. Hinton. The campaigns were organized using common sense principles and althoueh there was little technical input into the field exercise, there was the great advantase th a t a c t i o n w a s t a k e n q u i c k l y . E x p e r i e n c e in Europe shows how remote the chances of successwould have been if the populations had been allowed to spread more widely. T ' h c c o y p u e r a d i c a t i o n c a m p z r " i e n w o u l d simplv not have becn undcrtakcn wi t h o u t d e t a i l e d t e c h n i c a l a s s e s s m e n t s o f ' t he efibrt and costs required and the lik e l y c h a n c e s of ' s u c c e s s . T h e s e a s s e s s m e nts were onlv achiel'ed b,u o long term stu d y o f p o p u l a t i o n c c o l o g y , t a r q e t e d t o a particular control application. 'l'his stu d y i n c l u d e d o p e r a t i o n a l e x p e r i e n c e a s well as applied ecolosv :rr-rdit is sie n i f i c a n t t h a t t h e a r s u m e n t s f o r s u c h p r actical details as the inc'entive bonus scheme cramefiom biologists. O n e r e a s o n t h a t t h e e r a d i c a t i o n o f m u s k rats and coypus could be considered was that their populations were confined to reasonably small areas with no im m i g r a t i o n . H o w e v e r , e v e n i n o t h e r s i t u a t ionswhere eradication is not possiblc, for example where large scale immisration from a neighbouring country 5 0 L . N , t .G O S L I N C ; A N D S . J . B A K E R c o n t i n u a l l y r e p l e n i s h e sa c o n t r o l l ed population, the principles which emerge in c o n s i d e r i n g t h e r e m o v a l o f - m u s k rats and coypus can be applied. Indeed, these p r i n c ip l e s m a y b e a p p l i c a b l e t o the sensiblemanasement of any population of v e r t e b r a t e s .M o s t i m p o r t a n t i s t h e need for applied population ecology, so that t h e r o l e o f v a r i o u s f a c t o r s , i n c l u ding control techniques in limiting the subject p o p u l a t i o n c a n b e e v a l u a t e d . N ext there must be a target population density over a defined area which can be independently mor"titored.This target could be e r a d i c a t i o n o r a d e n s i t y l o w e n o ueh to preclude environmental damage. In the c o y p u c r a d i c a t i o n e x e r c i s e ,t h e c ontrol organization was centralized becausethe aim was to eradicate a single population but a coordinated systen-rof local organizations might sometimes be more appropriate. Next, the peoplc carrying out the control in the field must be rewarded for achievir-rgtheir objective and n o t f or f a i l i n g t o d o s o ( a s w i t h b ounties). However, where incentive schemesare u s e d , r e s u l t s n e e d t o b e i n d e p e ndently monitored. In thc campaiun against c o v p u s , e s t i m a t e s o f t r a p p i n s e f l brt, population trends and the results of-field c h e c k sw e r e p a s s e dt o t h e c o n t r o l orsanization and this trelped both directly and i n s t i m u l a t i n e t h e e f f o r t s o { - t h e t r appers. 'I'hi

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