NUTRIA PROJECT

BASIC ECOLOGICAL STUDIES FOR THE Myocastor coypus SUSTAINABLE HANDLING IN ARGENTINA

EXECUTIVE FINAL REPORT OF THE FIRST STAGE

JANUARY

2005

RESEARCHERS AND TECHNITIANS WHO PARTICIPATE IN THE PROJECT Coordinators Lic. Roberto F. B: Laboratory of Regional Ecology, Department of Biological Sciences, School of Exact and Natural Sciences, University of Buenos Aires. E-mail: rober@bg.fcen.uba.ar Lic. Gustavo Porini: Wild Fauna Direction, Secretary of Sustainable Development and Environmental Policy. E-mail: gporini@medioambiente.gov.ar Researchers Lic. Maria Jos Corriale: Laboratory of Regional Ecology, Department of Biological Sciences, School of Exact and Natural Sciences, University of Buenos Aires. Lic. Santiago Manuel Arias: Laboratory of Regional Ecology, Department of Biological Sciences, School of Exact and Natural Sciences, University of Buenos Aires. Professionals and Technician who participate in the Project University of Buenos Aires Lic. Sofia Nazar Anchorena Dra. Alejandra V. Volpedo Lic. Gernimo Galvani Dra. Florencia Kleinman Province of Buenos Aires Lic. Alfredo Vilches Lic. Miguel Busatto Province of Crdoba Lic. Marcelo Alvarez Lic. Claudia Zana Lic. Leonardo Barrios Caro Lic. Pablo Michelutti Province of Corrientes Vet. Guillermo Cao Lic. Maria Luisa Sanz Mr. Ovidio Eclesias

Province of Chaco Mr. Livio A. Navarro Mr. Juan Verdn Province of Entre Rios Agr. Roque Fernandez Prof. Jose Osinalde Mr. Federico Prongu Mr. Luis Boroni Province of Formosa Lic. Franco del Rosso Mr. Abel Vzquez Lic. Natalia Ceresoli Province of Santa Fe Lic. Liliana Moggia Agr. Juan Carlos Rozatti Lic. Maria del Carmen Bovda Lic. Roque Quiani Elia M. Pascual de Vaccari Wild Animals Station of Breeding Vet. Virginia Rodriguez Vet. Jorgelina Echeverra Vet. Laura Sybut

INTRODUCTION

The coypu, quiy or false nutria (Myocastor coypus) is a relatively big rodent, of amphibian habits, native of great humid soil systems of the South East of South America (Parera, 2002). Its herbivorous nature, its relatively high reproduction rate, its tolerance to a wide range of climatic and hydrologic conditions and its high abilities of dispersion and colonization, turn it into one of the most representative and historically more abundant species in Argentina (B et al., in press), in particular the subspecies M.c.bonariensis, which lives in the basins of our big rivers (Paraguay, Paran, Uruguay and la Plata) and the Pampas lagoon systems (Nazar Anchorena, 2004).

Fig. 1:The coypu (Myocastor coypus) representative species and main resource of wild fauna in Argentina.

Its interaction with men is very old. Guaranes, chan- timbus and querandes, among others, used its meat as food and its fur to make their clothes. Later, the criollos intensified its benefits also for their survival, but encouraged mainly for the commercial demand for its fur.

Fig. 2: The coypu is highly prized for its fur and also for its meat. In this picture you can see a hunter from Corrientes, collaborator in our project starting to skin an animal just hunted.

Its sale (tanned or not) is and has been very important for our country (until 1997 around 5.000.000 furs were exported annually) (B, 1999). For many decades, the number of exemplars captured, the significant amount of people involved in the different links of the commercial process (hunters, stockpilers, tanners, furriers, exporters, etc.) and the volume of money moved, determine that the coypu is the main resource of wild fauna of the country (Bertonatti and Corcuera, 2000).

a

b Fig. 3: Our country exports up to 2.500.000 tanned nutria furs annually. a: A typical fur lot just tanned. b: A technician making the process of finish of the nutria fur.

Yet, until recently, the scientific research carried out to the coypu in its natural and original environment was scarce and disperse. Besides, it could be hunted during an official season (autumn - spring) not fixed with ecological criteria, but clearly logical as it is in the coldest time of the year, when the plush of the fur of the coypu is thicker and therefore is more priced. (Porini et al., 2002.a.).

As a result, since the year 2001, researchers and technicians of the Wild Fauna Direction, its pairs in Buenos Aires, Entre Ros, Santa Fe, Corrientes, more recently Chaco, Formosa and Crdoba (and also Santiago del Estero and Ro Negro) and the School of Exact and Natural Sciences of the University of Buenos Aires, we have been carrying out the so called Nutria Project. Basic ecological studies for the Myocastor coypus sustainable handling in Argentina (B and Porini, 2001). GOALS

The basic goals of the first stage of the Nutria Project (of three years of length) were: a) to generate basic bio-ecological information about the Myocastor coypus, b) to suggest and try

methodologies suitable for its obtention and c) to evaluate the state of situation of its wild population and its habitat in the main nutria areas of Argentina.

Based on the knowledge generated, we have started an action plan which, from relatively simple and concrete measures, intends to contribute with the sustainable handling of the species, with the humid soils it lives in and with the improvement of the life quality of the human communities that have traditionally used the coypu resource in our country. In order to reach such goals we are working in the following aspects:

i. Analysis and evaluation studies of the habitat aptitude for the species at different temporal and space scales

ii. Density estimations and other basic population parameters. iii. Evaluation of the modalities and intensity of the coypu hunting. iv. Application of models to evaluate the sustainability of the hunting. v. Evaluations of the physical condition and sanitary state (internal parasites) of the

individuals. vi. Generation of complimentary information about the species in areas of little nutria

activity and in urban humid soils. vii. Development and trial of capture and immobilization in the field, determination of

age and indirect estimations of the density in different kinds of environments. viii. Integration of the information obtained in the previous items in a model of

relationships and in the development of a methodology of evaluation associated which enables to establish the existing relationship between the relative ability of the habitat and the abundance and stability of its populations, incorporating the cynegetical factor.

The final elaboration of the model and the implementation in the field of the methodology associated before mentioned are an essential part of the second stage of the project whose beginning is scheduled for 2005.

In this stage, we intend that the administrative measures which are taken in connection with the nutria resource have an adequate scientific support, with precise tools, which should be realistic in terms of effective possibilities of implementation and that enables the generation of information at scales according to the decision making from the users and the official administration organizations.

MATERIALS AND METHODS

For three years, in 25 pilot areas specially selected by the representatives of technical organizations before mentioned, and in contrasting times from the climatic-hydrological point of view and the nutria activity that takes place in them (on and off authorized hunting season), we have carried out the following activities:

Fig. 4: Location of the 25 pilot areas in which, since 2001, the Nutria project has been taking place. Partial goal I.: the Myocastor coypus habitat was characterized, and it was analyzed the pattern of use/selection of resources that the species make at macro scale (at a type, quality and size level and relative space disposition of the different environments that makes the typical landscape of pilot areas) and micro (considering variables such as the percentage of covering of the dominating vegetable species and the depth and permanence of water, among others).

a b

c Fig. 5: The characterization and the studies of the habitat use are carried out at three levels of analysis. A: Landscape pattern. B: Component environment of that landscape ( Macro scale). C: Physical and vegetation variables (Micro scale). Assuming a direct relationship between the habitat aptitude and its intensity of use, classical use methodologies versus resources availability were applied (Manly et al., 1993), using signs or hints of the activity of the species (nests, food areas and paths), surveyed through transects.

Fig. 6: Professionals and technicians of the province of Entre Ros analyzing signs of the presence of nutrias. Once checked their adequate detection, they enable us to evaluate not only the intensity of use of the different environments (or their components ) but also to establish they did it with shelter-reproduction purposes, food and/or movement respectively (B and Porini, 2001).

Partial goal II.: indirect and direct estimations were carried out of the density of coypus through methodologies based on the analysis of signs and hints and on captures by removal respectively (see point VII)

From the animals captured, other basic population parameters were estimated such as the sex proportion, the percentage of pregnant females, the average size of the litter, the gross productivity, the population increase rate and the structure of ages (B and Porini, 2003). For this last parameter different methodologies based on the analysis of different variables were tested and developed. They were relatively easy to measure in field conditions (see point VII).

Partial goal III.: through field samplings and interviews adequately designed to key informants (B et al., 2002), precise information was obtained in terms of the hunting time, the size of the hunting areas and their permanence, the number of traps used, the selectivity and efficiency of capture of the hunters, its dedication to the activity and persistence and intensity of the coypu hunting in the different areas under study (B and Porini, 2003).

Fig. 7: Professionals and technicians of the Fauna Direction of the Nation and the provinces of Corrientes and Entre Ros making indirect estimations of the densities of nutrias.

Fig. 8: During the Nutria project, several interviews to hunters were carried out. This collaborators (local inhabitants) gave us information of the modalities and intensity of the nutria hunting in pilot areas.

Partial goal VI.: From the evaluation of the information pointed out before, and using some of the parameters estimated in II, three models were applied to evaluate the sustainability of the hunting (besides considering in particular the structure of ages pointed out in point II.): the susceptibility model (SM) (Nazar Anchorena, 2004); the harvest model (HM) and the stock recruiting model (SRM) sensu Bodmer et al. (1997) (B and Porini, 2003). The SM considers two basic aspects which would influence the susceptibility of the population to the

declination in their size: the longevity and the time of generation (Pimm, 1991) (estimated as the age of the oldest and youngest pregnant female respectively). The HM analyzes specifically the proportion of production that is harvested, using as an estimator of the production the annual reproductive productivity multiplied by the density of females in each hunting place (Bodmer, 1994). Finally, the SRM considers the relationships between recruiting rate and the population size, assuming that a maximum sustained performance of coypus could be obtained, harvesting up to 60% of their population as long as they are close to the loading capacity (k). In such case, k was estimated as the average population density observed in sites with no hunting activity (Bodmer et al., 1997).

Partial goal V.: in order to describe the physical condition or general state of the individuals of the different areas studied, it was estimated the rate of condition proposed by Bailey (1968) which was also used by Willner et al., (1979) for M. coypus. In addition, it was analyzed portions of liver and intestine and feces of the most part of the individuals captured to evaluate their sanitary state describing, in this case, the most frequent parasitosis.

Partial goal VI.: as an important complement of the activities that have been taking place in the main nutria areas of Argentina (located mainly in the Parana-platense basin and in the Pampasia Salado system and of the courses of the Atlantic slope of the province of Buenos Aires), it was carried out similar studies to those before mentioned in the Reserve of Biosphere Laguna Oca of Paraguay River (Formosa) (B et al., 2004). To evaluate the past and current situation of the coypu was particularly useful, not only due to the singular functions that a reserve of this kind could fulfill (CMA, 2001), but also due to its particular location, adjoining with a city of high population density (Formosa) and inside the flood valley of the Paraguay river, considered a typical area (according to the classical maps of natural distribution of the species) but however, little important in terms of the nutria activity, at least at present (Arias et al., in press).

On the other hand, taking into account, that most of the ecological studies made in the framework of this project, came from natural areas with environmental conditions different from the urban humid soils and being practically unknown the effects of the activity of the coypu in artificial environments in our country, we also carried out habitat and population studies in this kind of environments, specifically in lagoon areas (and their surroundings ) of the Golf Course of the City of Buenos Aires (GCCBA) (Corriale, 2004).

Fig. 9: Through measurements in laboratory, the physical condition and general state of the individuals captured state is analyzed ( In the pictures we can observe the different tasks carried out in the ECAS (Station of Wild Animals Farming La Plata Province of Buenos Aires).

a b

Fig. 10. As an important complement, population and habitat studies in urban and periurban humid soils were carried out. In the pictures we can observe two typical landscapes of a: the Reserve MAB Oca Lagoon of the Paraguay River (adjoining with the city of Formosa) and b: of the Golf Course of the city of Buenos Aires.

Partial goal VII.: as a basic supply of the project, different methodologies were developed and tested to carry out captures alive and to chemically immobilize M.coypus individuals, estimate its age and density indirectly.

For the test of captures alive the kind of traps called tomahawk of 75 x 35 x 35 cm were made up, testing its efficiency, effectiveness and selectivity. Also it was evaluated the preference of the coypus for different kinds of baits (potato, carrot, cabbage). As regards chemical immobilization of the individuals, it was evaluated the effect of different drugs combinations (at different concentrations) with sedation and anesthesia purposes (Corriale, 2004).

For the age estimation, it was evaluated different methodologies based on the analysis of the dry weight of the crystalline, length of the foot and length of the tail (Pascual de Vaccari, 2002), the weight (Norris, 1967; Crespo, 1974) and the total length of the individuals (Colantoni, 1993) and it was suggested other two methodologies based on the measurement of different cranial morphometric characters and on the eruption of the teeth (Nazar Anchorena, 2004)

To estimate indirectly the population density of M.coypus, different methodologies were carried out. One of them, whose use is suggested for environments of the kind of estuaries, is based on the analysis of basic characteristics and the relative space disposition of three kinds of signs of the presence of the nutria (nests, food areas and paths) (MDRS) (B, 1996). The three remaining ones, were tested for streams environments and/or lagoon with banks and borders of high slopes and they are based on the analysis of the size and the relative disposition of the hypogeous entrances of their caves, of the feces and/or of both types of signs considered as a whole (Corriale, 2004). All the methodologies before mentioned were tested in field conditions and its precision was evaluated through the comparison of the results with those obtained through a direct method making captures with removal and based on the probability of capture (RCM) (Zippin, 1958).

Partial goal VIII.: Finally, from the existing relationship among the different types of results obtained, it was suggested a descriptive-predictive model and an associated methodology of evaluation that, fed with a great deal of information contributed in the previous points, enable to evaluate the aptitude of habitat for the nutria (through a habitat adequability rate or HAR of own development) with the abundance and stability of their population (even incorporating the effect of the hunting pressure) (B and Porini, 2001). RESULTS AND DISCUSION I. Analysis and evaluation of the habitat aptitude at different scales. The coypu would use to cover all its habitat requirements (at a macro level ), only the environments located in the relatively lowest portions of the topographic gradients, characteristic of the big fluvial lacustrine basins of our country. Basically, lagoons and estuaries (and in less degree, water courses of low order) with rooted vegetation of high and medium cover (preferably distributed in areas of thick growth), variable percentages of aquatic lows, high permanence of water and with 35 cm medium depths (range 10-65 cm)

a

b

Fig. 11: The lagoon or estuaries environments with areas of thick growth of tall herbaceous and variable percentages of aquatic vegetation are selected by the coypus to satisfy its requirements of food, shelter and reproduction. In the pictures we can observe two typical environments located in the provinces of a: Entre Ros and b: Buenos Aires.

This fact would relate (at a micro level ) to the relatively best material resources and conditions that, in terms of shelter-reproduction are given by the areas of high rooted herbaceous (70% cover) where they build their nests (basically of rushes Schoenoplectus californicus -) and the wide prairies of low and medium aquatic where they find food (mainly of saeta -Sagittaria montevidensis-, water hyacinth -Eichhornia spp. and Limnobium spp.-). Such environments would give them a bigger protection in front of predators (including men) and would make their shipfiting easy, considering the swimming habits of these species (B and Porini, 2001).

a

b

c

Fig. 12: Description of a: a nest b: an area of food c: a nutria path observed during the samplings in field.

If the values of height and slope of the border are adequate (Medium (M) = 60 cm, 20-115 cm and M = 75 cm, 45-85 cm respectively) they also build caves and if the aquatic vegetation is scarce, they feed on tender pastures of middle hill (like Luziola peruviana, Cynodon spp and

other species) although they do not go far from the water (M = 13 m, range 4,5-25 m) (Corriale, 2004).

It is very important to point out that, if we want to evaluate if an area is more or less apt for the species, not only the stability and depth of the water and the kind and size or quantity of vegetation rooted and floating must be considered, but also, essentially, its relative space disposition. Namely, the coypu would be a border species that uses basically a fringe not wider than 4 m wide (M = 2,5 m, range 2-4 m) between the close and open environments to satisfy its habitat requirements (B and Porini, 2001; Porini et al, 2002.b).

II. Density estimations and other basic population parameters The average coypu density for all the areas under study was 1.67 individuals/ha, although it was observed an important variation among different kinds of environments and, essentially, among the seasons with and without hunting (range 0,10 4,97 individuals/ha respectively) (B and Porini, 2003).

The proportion of sexes observed was 1:1 in 91% of the modal areas, prevailing the individuals sexually mature (89,7%). At the start of the hunting activities, the percentage of females pregnant was 69% (range 43- 94%). On the other hand, it was observed that there would be two moments of the year where there are peaks of parturition: halfway through autumn and halfway through spring (fact that coincides with the beginning and end of the hunting season authorized in the main nutria provinces of the country, contributing with an important loss of potential production of the species). The average size of litter is a little more than five individuals (M = 5,4 range 4 -7) and the gross productivity (total number of fetus/total number of mature females) of 3,6 (B and Porini, 2003; Nazar Anchorena, 2004).

The population increase rates were relatively high in most of the cases studied (average value 1,050,26; range 0,5-1,39), being similar to those pointed out by Robinson and Redford (1991) as typical medium mammals (Nazar Anchorena, 2004).

In connection with the age structure, during the hunting season authorized, in 64% of the modal areas (where hunting is relatively intense and persisting), prevailed individuals of short age (young and sub-adults) (79% average). The average age of the animals was 1.1 years and individuals older than 3 years old were seldom observed (values far lower than 6.3 years of potential longevity estimated for the species Gosling and Baker, 1981-). Additionally, the average age of the youngest females pregnant was 8 months old and the oldest 20 months old (Porini et al., 2002.b.; B and Porini, 2003; Nazar Anchorena, 2004).

III. Modalities and intensity of the hunting activities From the results obtained, not only from the interviews, but also from the samplings made in field, appeared that: the nutria hunters focused their hunting activities in winter (80%). However, at least 50% starts their activities in autumn and 40% extends them long after spring begins. On the other hand, at least 10% continues hunting off the authorized season, 100% does it in environments of the kind of estuaries (as we have described before) and 10% does it also in streams with vegetation and/or lagoons with borders of relatively high slopes (B and Porini, 2003).

The average size of the hunting areas (individual) is 30 ha (range 15 45 ha, with absolute maximums slightly bigger than 100 ha) and their permanence in them is around 15 days

(range 3-25 days). The average number of traps used daily by each hunter is 15 (range 5-40), its average efficiency is 40% and the smallest 15%. Around 9% also hunts with dogs and shotguns. Our results show that any of the two modalities mentioned would be selective neither by sex nor groups of age (despite the effort most of the hunters make by placing their traps at depths which ideally would mean only the capture of adult individuals) (B and Porini, 2003).

As regards the dedication to the activity, 80% of the nutria hunters do it persistently and dedicatedly, which means that although they do other farming activities, during the authorized season they devote themselves exclusively to the nutria hunting year after year. Practically, 50% of these people do it with a high intensity, namely, they get to hunt more than 1000 exemplars a year. The remaining 50% captures, average, nearly 400 individuals a year (B and Porini, 2003). IV. Models application to evaluate the hunting sustainability The results obtained from the application of the SM, HM, and the SRM models showed a variable outlook. In spite of what was pointed out in II, as regards the structure of ages observed and its probable relationship with the relatively intense and persisting hunting activities, the coypu population would be, by the SM (and the intrinsic growth rates estimated) little susceptible to the local extinctions. Nevertheless, we would be observing a slight tendency to a decrease (or a smaller increase) of their sizes related with times of generation relatively larger (Nazar Anchorena, 2004).

On the other hand, from the simultaneous analysis of the HM and the HM and SM, as Bodmer suggests (com.pers.) in his unified harvest model, he would suggest that, in at least 40% of the nutria areas of the country there would be an overhunting taking place. Yet, in some of these cases, such overhunting would be covered by compensatory effects related to still high demand of existing habitat in most of the nutria areas of the country (point I.) together with the high reproductive, dispersive capacities, and own colonization of the species (B et al., in press).

a

b Fig. 13: during the authorized season, many country people are exclusively devoted to the nutria hunting getting to capture more than 1000 nutrias a year. In picture a: we can observe, a hunter, collaborator of the province of Buenos Aires, after a day of capture, and in b: the nutria leathers in the drying stage.

However, we must take into account that if there appears any natural factor not contemplated until now (such as diseases, modification in the hydrological diet caused by floods -B and Malvrez, 1999-, extraordinary droughts or the implementation of infrastructure works for the handling of water -B and Quintana, 1999-), the compensatory factors mentioned could

stop acting with negative consequences or, at least, uncertain for the species and the human communities that live on this wild fauna resource.

V. Evaluations of the physical condition and sanitary state of the individuals

In close relationship with what was explained before, he suggested that in almost all the nutria areas of the country, despite the eventual numeric compensation that would be taking place from one year to the other, the physical condition would be deteriorated. The average value of the rate of condition was relatively low (M = 3.61 range 2,34 5,59), considering its values in places where the coypu does not suffer hunting pressure (see point VI.). On the other hand, the lowest values observed corresponded to places with relatively bigger historical intensities in terms of the hunting pressure of the coypu (B and Porini, 2003; Corriale, 2004).

In connection with the sanitary state, the feces and viscera analysis carried out until now showed, as it was pointed out in some previous local works (Moggia, 1981; Colantoni, 1993), the presence of a helminthical fauna particularly diverse, in which the digeneous stands out from the Hippocrepis, Athesia y Taxorchis kind, and some species of cestodes, still in the identification stage. On the other hand, it is particularly important, the absence of hepatic Fasciola in all the animals examined (Galvani, com.pers.).

It was concluded that, according to a great part of the results pointed out in points III, IV and V, it was necessary to restate some of the modalities of hunting and of the current measures of handling, as such might be affecting negatively the coypu population. As a consequence, it was suggested : a) to shorten the season of authorized hunting, concentrating it only in winter months (in order to avoid huge losses of potential productivity caused by hunting taking into account the estimated times for the peaks of appearance of the species); b) to recommend to avoid the hunting with dogs (as it would not be selective by etarian groups) and c) not to diminish the size of the leather allowed, and not to accept, as it was happening in recent times, any percentage of leather under such size so that the hunters make a bigger effort to capture adult individuals (avoiding placing their traps in the caves or nests or in dry paths, where they would catch adults as well as the young ones, and at a depths lower than 15 cm, so that the litter or young individuals swim past on top of these) (B and Porini, 2003; Nazar Anchorena, 2004).

vi. Complementary studies in urban and periurban humid soils (natural and artificial) without current nutria activity The results obtained in the periurban humid soils of the Reserve MAB Laguna Oca, from the interviews as well as from the studies carried out in field, would point out that the coypu would be practically absent in the area (M = 0 individuals/ha; range 0 1,47 individuals/ha) (B et al., 2004).

Even though the habitat supply would be adequate (although relatively lesser than other humid soils of the country in aspects related to the level and water stability and the coverage and variety of vegetation), this situation would be the result of a historic overexploitation related with the marginal economies of great part of its inhabitants and the lack of adequate controls. We could add to this, at present, the advance of the urban frontier, the action of natural predators practically absent down in the water such as the alligator (Caiman spp.) and the effect of great floods (Arias et al., in press).

Fig. 14: The samplings in field carried out in the Reserve MAB Laguna Oca (periurban) indicate a lesser habitat supply for the species and a low density probably related to a historic overexploitation.

For what was explained before, we have set up a plan of population reinforcement (UICN, 1998), which could contribute with the recovery of the coypu in the area, giving a productive alternative for the villagers following (and making them comply with) the Program MAB outlines (UNESCO, MAB, 1996).

On the other hand, in the artificial humid soils of the CGCBA (Golf Course of the city of Buenos Aires) it was observed that the intensity of use from the coypu for the construction of its shelters (mainly caves) was particularly conditioned by the slopes values (M = 75; range 47-85) and the height of the banks ( =X 61,2 cm; range 19-114 cm) and that its shifting out of the water (M = 13 m and maximum values of 108 m) was bigger than those suggested by other authors (Doncaster and Micol, 1989; Guichn, 2003) and made with food purposes. This originated several clearings in the vegetation (average values of 1.1 m2 of diameter and maximums of 19 m2) with the subsequent damages in the surrounding park (Corriale et al., in press).

As regards the population parameters, the densities would be relatively high ( =X 3.44 individuals/ha; range 0.65-6.03 individuals/ha) reached in periods relatively short (less than two years), as well as the condition rates ( =X 5.18; range 4.69-6.63). These last rates, along with the sexes proportion (1:1) and structure of ages observed (6.2 % of adults), would indicate adequate perspectives of population growth (Corriale, 2004).

It is considered that the absence of hygrophile vegetation in the water and the presence of food resources out of them in a continuous way, (despite relatively less quantity), along with the tranquility conditions in the busiest hours of the coypus (Palomares et al., 1994), hunting absence and natural predators, would determine that the coypu behaves as a plague in this kind of humid soils (Corriale, 2004).

As a result of what was explained before, measures were suggested based on periodic campaigns of reduction of population number and on a lesser control of the growth of aquatic vegetation in lagoons (so that the animals can satisfy all their life requirements inside them).

This way, we would contribute with a harmonic relationship between the human activities and the presence of the coypu in this particular kind of environments (Corriale et al., 2004).

a

Fig. 15: The absence of hygrophile vegetation in the lagoons and the slopes adequate for the construction of shelters (photo a) determine that the coypu behaves like a plague in urban humid soils. In photo b: we can see a food area of great size in the Golf Course of the city of Buenos Aires.

b VII. Development and test of capture and chemical immobilization methodologies, age determination and indirect estimations of density in different types of environments. In connection with the tests of capture alive carried out with jail-traps, satisfactory results were obtained, as 98% of the individuals captures through them, would not suffer any kind of injury. Its efficiency and selectivity are around 93% y 97% respectively. On the other hand, although its efficiency was rather low (20%), it was higher than that obtained by other authors (Doncaster and Micol, 1988; Guichn, 2003). Finally, although there were not differences among the different types of baits used, we recommend the use of carrots for their high degree of acceptance and their relatively low cost (Corriale, 2004).

Fig. 16:. Traps developed during the Nutria Project to carry out captures alive of these animals..

From the experiences of chemical immobilization, there appeared recommendable doses of ketamine hydroclhoride and of acepromazine maleate for the sedation (0.96 mg/kg and 0.048 mg/kg, respectively) and of ketamine hydroclhoride and xilazine hydroclhoride for the eventual anesthetizing of the animals (4 mg/kg y 0,5 mg/kg, respectively). The latter was similar to the one suggested by B et al. (1994) and it would be the most recommendable one to enable an adequate manipulation, without altering substantially any physiological parameter ensuring an adequate and relatively fast recovery of the animals (Corriale, 2004).

Fig. 17: During the Nutria Project many experiences of Myocastor coypus chemical immobilization were done, which resulted useful for the anesthetizing, sedation and manipulation of these animals.

From the evaluations of different methodologies suggested to estimate the age in Myocastor coypus appeared that, although the one based on the dry weight of the crystalline would be more precise (Pascual de Vaccari, 2002), those based on the determination of the body weight and the measurement of three cranial morphometric characters (basal length, total cranial

length total and total mandibular length) would be the most recommendable ones taking into account their relatively high precision, simplicity and facility of implementation in field conditions (Nazar Anchorena, 2004; Corriale, 2004). The cranial morphometric characters previously mentioned would constitute, besides, a useful tool to evaluate a posteriori the effect exercised in the populations exploited through the study of the ossuaries that are usually found in the campsites once the hunting season is over.

Fig. 18:. An ossuary found in a campsite of non-residing hunters. The methodology developed to estimate the age from morphocranial characters is particularly applicable to them.

In connection with the method based on the relative disposition of signs (used in estuary environments), the results obtained would point out that it has a relatively high precision compared with the RCM (r = 0.77), differing both estimations in no more than 0.65 individuals by hectare (B and Porini, 2003).

As regards the methodologies developed for stream and/or lagoons environments (of margins with relatively high slopes), of the three methods suggested, the one based on the analysis of the caves systems (MASC) would be the most adequate one for its relatively bigger facility of application, and, essentially, for its high precision when comparing its results with those obtained by the direct method (r= 0,96) (Corriale, 2004).

As a consequence not only the MDRS but also the MASC, would be, according to the kind of prevailing environment, the most recommendable methods to carry out periodic estimations of density of M. coypus without the need to capture individuals and altering in any way the habitat.

VIII. Model and methodology of evaluation of the relationships of aptitude of habitat-abundance and population stability.

In connection with the model and methodology of evaluation developed, although they are still at an experimental stage, the tests carried out in a pilot area during three years, would be

challenging at pointing out a positive association (with adjustment to a logistical model) among the variables before mentioned. This would imply that, the high values of HAR would match with relatively high and steady densities (which means with smaller variation coefficient through the time). It is intended that they would enable to predict from the HAR estimation, the coypu densities in the different nutria areas of the country (and at different scales or levels of detail), even taking into account, different possible values of loading capacity, which would be closely related with the hunting intensity in the areas.

CONCLUSIONS AND FINAL CONSIDERATIONS

In the first stage of the Nutria Project, we have started to generate solid bioecological information in order to find out and compare the reaction of the M. Coypus populations before the changing conditions of its environment and the human pressure in terms of its abundance and physiological condition, incorporating its variability in space and time.

In connection with the methodologies developed and/or tested through the time, we thought that many of them would be relatively precise and easy to implement, would have an adequate predictive character and its use would practically not alter the population and the natural surrounding of the nutria.

We consider that the bio-ecological information generated, as well as the methodologies described, can be applied to ecological scales (space and temporal ones) closely related with the usually requested ones for the decision-making from the administration organizations of wild fauna.

Some of the methodologies mentioned, as the one for the age and population density estimation, are already being implemented with adequate results and part of the information generated has been translated into concrete handling measures, as those suggested in terms of the modalities and authorized hunting season in the main nutria areas and the suggestions of reinforcement or population control in some urban and periurban humid soils. Even though we are aware of the need to continue to go deeper and adjust each subject before explained and to incorporate new ones, we believe that the latter should not be an excuse not to give any kind of handling recommendation, at least a provisory one (and a precautionary one), while we advance in the necessary knowledge.

Another remarkable aspect is that in our project we have worked in an integrated way, representatives of research and administration organizations (national as well as provincial ones) and have favored the formation and training of researchers and technicians in these subjects. In addition, we counted with the invaluable collaboration of representatives of the local human communities, who told us their interests and views and gave us their great knowledge, generally wasted by the part of the technical-scientific community.

On the second part of the project we mean to integrate the knowledge generated in a predictive model of quantitative character based on the relationship habitat- population- hunting pressure, which enables to evaluate a priori the state of the population, incorporating the integrator concept of loading capacity and which leads, in the last resort, to express the results in terms as sustainable harvest, which can be translated into effectively in political-administrative measures adequately supported.

Undoubtedly, the challenge is very important. In the first place, because in Argentina and in the rest of Latin America, the limitations in terms of political support and economic means to carry out this kind of projects are very significant. On the other hand, because many times the trust of the models as the one mentioned before is low, in part, because the organizations related with science and the handling work are separate spheres. Science requires high levels of trust and precision and its standards are generally little applicable to the management decisions, particularly when the information is scarce and/or little spread, the space scales are relatively big the temporal scales are short. Aware of these difficulties, in the Nutria Project we will try to go on reducing them.

In connection with the new subjects to incorporate, we consider it is very important to study the possible synergic and compensatory effect that would have, in terms of the differential hunting pressure, the dispersive or migratory movements of these animals (for example, through fountain-cesspool Novaro et al. 2000-), which would occur in close connection with extreme events of floods and drought, which each time with more frequency, large areas of our country experiment.

Analogically, it is fundamental to analyze how the oscillations in the supply and demand at a commercial level can boost and/or compensate the risks of decrease in the coypu population. Such analysis should be part of a socioeconomic study program a lot wider in which it cannot be missing the studies related with the economic valuation of the resource and with the economic and social feasibility of its exploitation. Taking into account the situation of extreme poverty of many inhabitants of our country, the studies should tend to generate a real labor alternative based on the Myocastor coypus sustainable handling and , as such, to guarantee a more equal income distribution generated by its exploitation among the different agents that are part of the commercial circuit.

We intend to advance in the spread, regulation and adequate coordination of the legislation related with the use of this species and the fauna in general (at a provincial, regional and national level ) in its different modalities (survival, commercial and sport ones) (Bucher, 2002) Finally, we hope that each time the carrying out (and continuity) of research projects and the handling of species of wild fauna, as the one presented here is favored in our country (for example, through a bigger reinvestment of the resources generated by its use). As a result, we would count with more means and skillful personnel so that the necessary research tasks, monitoring and legal control are really effective and sufficient. We believe that, as Toribio and Sorouco de Madrazo (2001) claim, if we act like this we will be contributing to the benefit of our rural communities, keeping their environment and their basic resources, valuing their traditions and ways of life and giving them amore diverse and steady economic basis.

ACKNOWLEDGEMENTS

We would like to thank the authorities and personnel of the following institutions: Direccin de Fauna Silvestre de la Nacin; Laboratorio de Ecologa Regional, Dto. de Ecologa, Gentica y Evolucin (EGE) , Facultad de Ciencias Exactas y Naturales (FCEyN), Universidad de Buenos Aires (UBA); Direcciones de Fauna Silvestre de las provincias de Buenos Aires, Entre Ros, Santa Fe, Corrientes, Chaco, Formosa, Crdoba, Santiago del

Estero y Ro Negro; Comit MAB Argentino, Oficina Regional de Ciencia y Tecnologa de la UNESCO para Amrica Latina y el Caribe (ORCyT); Unidad Coordinadora de Administracin de Proyectos (UCAP) (Formosa), Estacin de Cra de Animales Silvestres (ECAS) (Buenos Aires), Laboratorios de Vertebrados y de Ecologa de Parsitos y Vectores, Dto. EGE, FCEyN, UBA, Federacin Argentina para la Comercializacin e Industrializacin de la Fauna (FACIF) y Campo de Golf de la Ciudad de Buenos Aires. To the following researchers and technicians, in particualar, for its active participation in the project: Sofa Nazar Anchorena, Alfredo Vilches, Miguel Busatto, Roque Fernndez, Jos Osinalde, Federico Prongu, Liliana Moggia, Juan C. Rozatti, Roque Quiani, Elia M. Pascual de Vaccari, Guillermo Cao, Mara L. Sanz, Ovidio Eclesias, Livio A. Navarro, Juan Verdn, Franco del Rosso, Abel Vzquez, Natalia Ceresoli; Marcelo Alvarez, Claudia Zana, Leonardo Barrios Caro, Pablo Michelutti, Virginia Rodrguez, Jorgelina Echeverra, Laura Sybut, Alejandra V. Volpedo, Gernimo Galvani y Florencia Kleinman. We would also like to thank the invaluable collaboration of the people, personnel and owners of the rural premises of Chascoms, Gral. Lavalle, Gral. Madariaga y Bragado (Buenos Aires); Islas del Ibicuy, Gualeguay, Victoria y Diamante (Entre Ros); Vera, Garay y San Justo (Santa Fe); Esquina y Mercedes (Corrientes); Formosa (Formosa); San Fernando (Chaco) y San Justo (Crdoba). The current project is part of a Cooperation Agreement between the Secretariat of Environment and Sustainable Development of Argentina and the School of Exact and Natural Sciences of the University of Buenos Aires and its funded through the Wild Fauna Direction of the Nation.

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