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defined as the number of animals in relation tothe number of traps placed; “efficacy” as thenumber of traps with devices “triggered” bythe entry of coypus over the total number oftraps triggered, and “selectivity” as thenumber of coypus (“target” animal) capturedin relation to the total number of other animalscaptured by the traps. The preference of thecoypus for different types of baits (potatoes,carrots and cabbages) was also evaluated.The results were satisfactory, since the 98%of the individuals captured by means of thetraps mentioned did not suffer any type ofwounds. The efficacy of the traps was 93%and the selectivity 97%. On the other hand,though the efficiency of capture was relativelylow (20%), it turned out to be higher than thatobtained by other authors (Doncaster andMicol, 1989; Guichón, 2003). No significantdifferences were found among the differenttypes of baits used. However, the use ofcarrots is recommended due to its greateracceptability in comparison to potatoes andthe relative low cost compared to cabbages(Corriale, 2004).Chemical immobilization of specimens wasevaluated according to the effects of variousdrug combinations in different concentrationsfor sedative and anesthetics effects (Corriale,2004). For sedation purposes, the advisabledose of ketamine hydrochlorate and ofacepromazine maleate was 0.96 mg/kg and0.048 mg/kg, respectively. For eventuallyanesthetizing the animals, the dose was ofketamine hydrochlorate and of xilazinehydrochlorate was 4 mg/kg and 0.5 mg/kg,respectively. The latter dose was similar tothat suggested by Bó et al. (1994) and itwould be the most advisable one since itallows an adequate manipulation of thespecimen (Figure 3), without substantiallyaltering any physiological parameter andassuring an adequate and relatively fastrecovery (Corriale, 2004).To estimate the age of the specimens, variousmethodologies were assessed based on theanalysis of: drained weight of the crystalline,length of the foot, length of the tail (Paschal ofVaccari, 2002), weight (Norris, 1967; Crisp,1974) and total length of the specimens(Colantoni, 1993). Other two methodologieswere proposed based on the measurement ofdifferent skull morphometric features and onthe eruption of the teeth on the gular series(Nazar Anchorena, 2004). A closeexamination of the different proposedmethodologies showed that even if themethod based on the drained weight of thecrystalline seems to be more precise (Paschalof Vaccari, 2002), those that aim atestablishing the corporal weight and themeasurement of three morphometric skullfeatures (basal length, total skull length andtotal jaw length) would be the most advisabledue to their relatively high precision, simplicityand easy implementation in field-researchconditions (Nazar Anchorena, 2004; Corriale,2004). The morphometric skull features wouldalso constitute a useful tool to further evaluatethe effects caused on the exploitedpopulations by studying the ossuaries that areusually found in the camps used by coypusmenonce the hunting season is over.Finally, different methodologies weredeveloped for the indirect estimations ofpopulation density of M. coypus. One ofthem is the method advanced by the relativedisposition of signs –MDRS– (Bó, 1996). It isespecially appropriate for the “marshy-lands”type of environment. This method is based onthe analysis of the structural characteristicsand the relative spatial disposition of threetypes of coypu-presence signs: nests, feedingareas and paths. In the case of stream and/orlagoon environments with high-slopedmargins or edges, three other methods wereput into practice. These were based on theanalysis of the size and the relativedisposition of the underground entrances ofthe caves (MASC), the feces and/or bothtypes of signs (Corriale, 2004). In all cases,these methodologies were analyzed in fieldconditions and their precision was evaluatedby means of comparing their results withthose through a direct method that implied theexecution of captures with removal, based onthe probability of capture (MCR) (Zippin,1958). The results obtained in relation to theMDRS would indicate that this has a relativelyhigh precision compared to the MCR (r = 0.77,p
coypus without the need to capture individualsand minimally altering their habitat, dependingon the type of predominant environment.load capacity, that may in turn be closelyrelated to the hunting intensity of these areas.RecommendationsFigure 3. The physical condition of captured specimens isanalyzed by means of in-house measurements (in thiscase, at ECAS – Station for the Breeding of Wild Animalsof the Province of Buenos Aires) (Photo: M. Corriale).I) Model and methodology for theevaluation of habitat suitability/abundanceand population stability.Finally, a descriptive-predictive model and anassociated evaluation methodology wereproposed on the results so far collected. Thismethodology, together with the findingsalready presented, would allow an evaluationof the habitat suitability for the coypu (bymeans of a “habitat suitability” index habitat –HSI–, developed specifically in this project)and an evaluation of the abundance andstability of the populations, incorporating theeffects of hunting pressure (Bó and Porini,2001).The model and methodology of evaluationdeveloped, though still at their experimentalphase, seem to provide encouragingperspectives, according to the analysis doneduring three years in pilot areas. The modeland the methodology show a positivecorrelation (adjusted to a logistic model)between the variables already detailed. Thiswould imply that high values of HSI wouldcorrespond with stable and relatively highdensities (that is to say, with smallercoefficients of variation through the years). Itis believed that such values will allow topredict the densities of coypu in the differentcoypu-exploitation areas of the country(expressed in different scales or levels ofdetail), even with different possible values ofThus having diagnosed the situation for thecoypus populations in the PAs under study–sections a) to e)–, it is now necessary toprovide some recommendations regardingsome hunting modalities and presentmanagement measures, since these wouldcause negative effects on coypu populations.The proposal, in this sense, is:i) To shorten the authorized hunting season,restricting it to the months of winter only,so as to avoid the enormous losses ofpotential productivity caused by hunt. Thiswould also consider the period estimatedfor the peaks of birth rates.ii) To ban hunting activities with dogs, sincethese would not be selective in terms ofage groups.iii) To increase the size of skins permittedfrom 65 to 70 cm (total length of theuntanned leather) and to reject any skinbelow that size, a practice it is notfollowed nowadays. The aim of this is totry to encourage hunters to focus theirefforts on capturing adult specimens,avoiding setting their traps inside caves,nests or dry paths, where they wouldcapture both adult specimens and youngones. Hunters are also advised to placetheir traps at depths above 15 cm to allowyoung individuals swim over them withoutbeing trapped (Bó and Porini, 2003; NazarAnchorena, 2004).Conclusions and final considerationsIn the first phase of the Coypu Project, wehave started to produce solid bioecologicalinformation in order to describe and comparepopulations of M. coypus facing changes oftheir habitat and the presence of humanpressure. This was done in terms of thespecies’ abundance and physiologicalcondition, incorporating variability parametersin time and space.Several of the methodologies developedand/or tested would be relatively precise, easyto implement and would have predictiveadequacy. Furthermore, their use would- 9 -
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