Kruuk, H.

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SECTIONVIIRELEASEOF CAPTIVE-BREDSPECIES:CARNIVORESH.KRUUKITE, Banchory1RELEASEOF CAPTIVEBRED SPECIES: MAMMALS,CARNIVORAGENERALThe observationson the effectsof the releaseof captive bred Carnivora, onwild populationsof the same or closely relatedspecies, generallyfall intotwo catergories: animalswere introducedto increasethe size of the wild populationwhich was deemed tobe threatened,andaccidentally,as escapesfrom captivityor domestication.In the first categoryfallsthe introductionof captive-bredotters in Norfolkand Suffolk. On the continent several introductions have taken place ofCarnivorain areaswhere theyhad been made extinctpreviously; this includesintroductionsof lynx (Lynx lynx) (Gossow & Honsig-Erlenburg 1986),bear(Ursusarctos)and others.In the second categorycomes the presence of feral cats (Fellscatus),dogs(Canis familiaris), and escapesfrom fur farms: mink (Mustela vison) andvariousfoxes, in many partsof Europeand elsewhere.The effectsof deliberateintroductionof carnivoresto increasethe size ofexistingpopulationshave not been assessed, and all evidence is anecdotal.However, somewhat more is known of the consequences of contacts betweenescapeddomestic (or feral)animalsand wild populations.2CASE HISTORIESOtters Lutra lutraThere have been severalreleasesof ottersin areas where the population wasdeemed to be too low, but thisusually involvedmere transplantation,and theeffects were not documented(Stephens1957,Willer et al. 1976, Kempf1981). The only substantial release of captive bred otters which has beendocumentedfor Europehas been in East Anglia (Jefferieset al. 1985, 1986).From 1983 until 1987 a total of 14 otters has been releasedthere (Wayre1988), in sites which were definedas 'gaps'between 'pockets' of remnantpopulations(Jefferset al., op.cit.). These remnantpopulationswere definedfrom the presenceor absenceof faeces (an unreliablemethod: Kruuk & Conroy1987). The range-sizes of otters were assumed to be smaller than 30 km.However,presentknowledge(H. Kruuk,pers. obs.) indicatesthat otters rangeover stretchesof river of 70 km or more; thus, the captivebred otters wereeffectively released into an existingpopulationwhich is declining (Jessop1985).The releasedanimalswere second,thirdor fourthgenerationcaptivebred, ofunknown,presumably English origin. Once released there was very littlefollow up. A few releasedotterswere followedby radio-tracking for somedays, in one case for 7 weeks; after that,all informationgatheredcame fromthe presenceor absenceof faeces (whichcouldnot be identifiedfrom those of'wild'otters). The releasedotters have been reportedto be breeding,andtheir offspring is also statedto have bred (Jefferieset al. 1986, Wayre1988). However,evidencefor all this is very circumstantial,and it was not3possible to assess the overalleffectof this releaseon otter numbers, letalone on geneticcompositionof the population. It is still unknownwhy otterpopulationsare so very low in East Anglia.WildcatFelts silvestrisThe species is widely distributed throughout northern Scotland, andinterbreedswith the domesticcat Fells catus (Frenchet al. 1988). However,hybridizationis limitedbecauseof a difference in habitat selectionbetweenthe two species; in general, wildcats tend to keep far from humaninhabitation, and domesticcats do not strayfar from houses (Corbett1979).There are relativelyfew feralcats in naturalareas on the Scottishmainland.Despite this, it has been established that modern wildcat populationsinScotlandcontaineda high proportionof hybrids.Most hybridization probably occurred earlierthis century, when wildcatnumberswere low. Becauseof this, the increasein wildcat numbersover thepast 50 years in Scotlandmay includemany hybrid cats (Frenchet al., op.cit.). Since wildcatnumbershave builtup, it is possible that there is nowless interbreedingwith F. catus,a phenomenonobserved in many other species(Szijj1966, Mayr 1970).There is some evidencethat the genotype of the modern wildcatsis returningto that of the old, 'pure'wild type. The modernwildcat populations appearto contain a smallerproportionof hybridsthan the populationsin the recentpast (French et al., op. cit.),and they resemble, therefore, the 'old'4wildcatsmore closely than do the wildcats from the more recentpast. It ispossible, therefore,that somewhatmore 'pure'wildcatpopulationswill againbecome establishedafter several furthergenerations.If the evidencepresentedby French et al. (1988),that the proportionofhybrids is decreasing,can be substantiatedthis then suggeststhat both feralcats and feral-wildcat hybrids are less viable (at least under Scottishconditions) than the wildcat, and that at least some effects of theintroductionof domestic cats on populations of wildcatscan be undone bynaturalselectionpressures.Feral dogs CanisfamiliartsThere was evidencethat a populationof feraldogs in Galapagos (Ecuador)wasgeneticallydistinct from domestic dogs on the islands,despitethe probablyfrequent contact (Kruuk 1979,Kruuk & Snell 1981). The feral populationstudiedhad started from domestic animals about 80 years earlier,and therewere many more domesticdogs on the islandsthan feral ones, of distinctlydifferentmorphologyand coloration. The feral dogs lived in an extremelyharsh environment. This evidence,as well as direct observationsof the feralpopulation,suggested a strong natural selection pressure in favourof aparticular phenotype,perhapsobliteratingfurthergeneticcontaminationfromdomesticstock.

Release of captive-bred species: Carnivores

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Release of captive-bred species: Carnivores

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