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Nigel Dunstone and Robert Strachan
Department of Zoology, Durham University, South Road, Durham City, DH1 3LE, U.K.
During 1986, at the invitation of Prodena Bolivia (Bolivian Wildlife Society), I accompanied a group of U.K. and Bolivian students on a visit to the Amboro National Park to conduct faunal surveys. It became obvious that there were good populations of otters present, and that these were potentially at risk from the activities of the campesino population. During the summer of 1987 we returned with a team of 14 people to undertake further survey work on the otters. The following resume is based on approximately 560 man-days in the field during the period July-September 1987.
The Park is bounded by the Rio Surutu and the Rio Yapacani on the northeast and northwest respectively and extends southward to latitude 17° 31', encompassing a pianigrafic area of approximately 180,000 hectares. Amboro is situated at the bend of the eastern slope of the oriental Andean range and divides the cooler and drier southern Andes fro» the wetter and more humid Eastern Andes in Bolivia. The Park is divided topographically into one-third lowlands ranging in height up to 490m and two-thirds upland foothills of the Andes extending to 2330m. The lowland area consists of primary rainforest interspersed with areas of cultivation and secondary forest, whilst the serrania is covered with primary humid rainforest.
Annual precipitation varied between 2000 mm and 3500 mm per year with the bulk falling between December and March. The Surutu and Yapacani are the principle rivers draining the Park (Figure 1) and flow into tho Rio Mamora a major tributary of the Amazon. The Rio Saguayo and its tributary the Yapoje flow into the Surutu approximately 10 km from its confluence with the Yapacani . The rivers Pitasama. Macunucu, and Semayo are also tributaries of the Surutu running southwest to northeast. The Rio Colorado is the major tributary of the Yapacani before its junction with the Surutu.
The rivers are primarily spate-rivers fed by the rain falling on the Serrania. The upper reaches are characterised by boulder-strewn rocky gorges whilst the lower stretches are slow flowing, silt-laden, and shallow during the dry season. A small number of ox-bow lakes (coriches) occur on the lower reaches of most rivers.
There is little published information regarding status and distribution of otters in South America (Thornback and Jenkins, 1982; Duplaix, 1978) and there is a dearth of information concerning otters in Bolivia. The species most likely to be encountered are the neotropical river otter Lutra longicaudis sp. complex, and possibly the giant Brazilian river otter Pteronura brasiliensis since this species is present on the Rio Mamora into which the Yapacani drains.
Anderson (1985) records both species as present in Bolivia but does not give locations or range. Riddle (1986) in a preliminary survey of the mammal fauna of the Amboro Park conducted in 1985 does not report the presence of Lutra or Pteronura . Nevertheless abundant signs of the neotropical river otter were recorded during our 1986 visit and evidence was collected locally that Pteronura had existed in the Park and may still be an occasional visitor. This was supported by an unverified report of a captive pair of Pteronura at the Santa Cruz Zoo, which were believed to have been captured locally. Anderson (pers. comm.) reports seeing an old Pteronura pelt. at the village of Beuna Vista on the edge of the Amboro Park from which it had presumably been collected.
Tello, in a report of a survey commissioned by IUCN, found Lutra longicaudis to b« widely distributed below 3000m in Bolivia but to be much reduced in numbers. He reported this species in all of Bolivia's National Parks including Amboro. In contrast he considers the distribution of Pteronura to be restricted to isolated populations in and around the Reserve Nacional de Fauna Manuripi-Heath in the Pando province.
The object of this study was to determine the status and distribution of otter species along the principle rivers of the Park and to identify «and assess the main factors affecting their distribution. The second part of the study sought to investigate the diet of the otters , and a qualitative assessment of the fishing activities of the campesino population in terms of areas fished, methods of fishing, species and numbers taken.
The rivers Saguayo, Yapacani, Colorado, Surutu, Pitasama, Macunucu and Semayo were all surveyed with particular attention being paid to the upper and lower stretches of the Saguayo. This river was extensively mapped and exhaustively searched for den sites and sprainting stations. Representative sections of the other rivers were then compared. In total 50km of river were surveyed, see Figure 1 for the extent of the area surveyed. Over 500 faecal samples were collected and their occurrence along the river courses mapped to give an indication of the relative density of otters. Figure 2 shows the deposition of otter spraint recorded between the 8-12th August along a 20km stretch of the Saguayo and the Yapoje. The majority of sprainting sites were located on sand bars where the faecal material was characteristically deposited in a scrape occasionally excavated to a depth of 20cm. Other sites included midstream rocks, promontories, fallen tree trunks, tree-root cavities, in hollows under boulders and in riverside caves. Rarely were more than four spraints found together in open locations whereas in sheltered underground sites as many as 20 spraints might be found. This was attributed to the activities of copraphagous hymenopteran insects (sweat-bees and ants) which were shown to be capable of dismembering and removing all trace of a 20g spraint in 6-24 hours.
Given the high density of spraints and their short longevity we consider the density of otters on the Rio Saguayo to be .very high. The Pitasama was the only other river where a comparable density of spraint was recorded. It was not possible to estimate the number of otters present or any details of their spacing pattern. Single otters were sighted on three occasions and breeding was confirmed by the observation of cub-tracks on both the Saguayo and Pitasama rivers.
To compliment the dietary analysis a survey of the fish species was carried out on the Rio Saguayo using fyke nets, gill nets, fish traps and rod and line. Twenty-one different species of fish were returned to the British Museun (Natural History) for identification. The species collected fell into five categories known to the local campesino fishermen under the general names of sardines and sabalo (Characins), bagre, caracha and surubi (siluroid catfishes) and benton. All these groups of fish were noted to occur in the faecal deposits of the otters, but the relative proportions of each type in the diet remains to be determined. Sabalo, surubi, bagre and benton are the species most commonly taken by fishermen. Although fishing activities within the Park are subject to control there is inadequate policing and the dynamiting and poisoning of rivers is commonplace (pers obs). Neither is there any control on the size of mesh employed by netsmen or any form of restriction on the fishing season.
Major threats to otters
It is common practise for poachers to dynamite pools for the shoaling species of characins e.g.. sabalo. Large quantities of fish obtained in this manner were offered for sale. We also received a report of an otter being killed when a pool was dynamited. Shock waves from the explosions have led to considerable bank erosion and collapse of holt sites. There was an absence of otter signs in areas that had been recently dynamited and for several kilometres up and down stream. Dynamiting was a nightly occurrence on some of the rivers. Interviews confirmed the use of both natural compounds, extracted from plants, and weed killer to poison fish in pools.
Despite a recently signed convenio between the campesino population and the CDF forbidding the felling of any tree within 100m of the river banks inside and bounding the Park, we found this practice commonplace. Similarly the cutting of chucio (Cana brava) for roofing continues. Since the roots of these plants bind together the sandy soil their destruction leads to severe erosion of the river banks. A number of government (servicio de caminos) and commercial companies are exploiting the sand and gravel for road building. This is causing considerable disturbance from lorries and the villages which have been set up to house the workers. Due to the impenetrable nature of the serrania the river corridors are used extensively as thoroughfares for the movement of crops e.g.. rice, maize and coca from the canpesino farms to collection points on the Surutu and Yapacani serviced by lorries. The number of campesinos allowed to farm in the Park is state controlled but there is no adequate policing with widespread clear-felling as new farms are developed even up to 14 km into the park. Furthermore the campesinos invariably have dogs which rely on scavenging and hunting for their subsistence. Dog tracks were found on most rivers and packs of semi-feral animals were observed. The farmers and hunters eat the meat of agoutis, pecarries, armadillos and tapir killed in the park. Evidence was also collected indicating that forest-living felids, including ocelot, jaguar and margay, are occasionally hunted for their pelts. Interviews suggested that otters are no longer hunted in the park because there is no market for their skins. No otter pelts were observed for sale or in caches confiscated by CDF officials.
Potential natural predators such as jaguar and puma are common in the park and their tracks were encountered alongside those of otters. No observations of anaconda or caiman were made although both species are reputed to occur. Dogs probably pose the most significant "natural" predator.
Status of otters on the rivers surveyed
This rivers Saguayo and Yapoje hold good populations of otter in the middle stretches. The higher reaches of the river have small populations of fish, particularly sardines, whereas the lower stretches were found to be heavily disturbed by campesinos and their dogs. A considerable area (c. 5km) in the middle reaches was denuded of fish due to dynamiting.. The Yapoje was found to be relatively undisturbed providing ideal habitat with pools containing abundant fish , considerable bank-side cover and suitable holt sites. Despite being overfished and disturbed in 1986 the Rio Pitasama has recovered and now holds considerable stocks of fish, particularly sabalo and caracha. Abundant signs of otters were encountered and the status of this river has improved considerably since the original visit in 1986 when dynamiting was commonplace. Disturbance has been much reduced by the cutting of a new access route through the forest to farms which obviates the need to travel along the river valley. The rivers Semayo and Macunucu were only briefly visited, here few signs of otters were encountered probably due to excessive disturbance. The Rio Surutu is the major thoroughfare into, and around, the park. It is subject to considerable bank-side clearance for agricultural purposes and the river is used for bathing, recreation and livestock wander freely. The river is commonly dynamited during the rainy season. Extensive gravel removal is occurring at a number of locations on the river. Nevertheless, otter signs were found throughout the length surveyed but were very sparsely distributed and most common at the confluence with feeder rivers. The Yapacani is the major river of the area; it is deep and fast-flowing even during the dry season. For this reason it is not used as a route into the park although it is crossed at frequent intervals. Gravel extraction is causing considerable disturbance at a number of locations. Otter signs were found throughout the area surveyed but more commonly on coriches and feeder rivers than on the main river. An attempt to survey the Rio Colorado, the major tributary of the Yapacani, failed due to its steep-sided gorge topography and the extremely deep water. The area is further protected by hordes of miraoue (blackfly, Simulidae) which discourage even the peasants from venturing there. t The Yapacani is extensively fished by netsmen.
From our interviews with hunters and campesinos it soon became evident that there is considerable confusion, both in the literature and in conversation over the species of animals that are present and the vernacular names they are given. The campasinos refer to 'El Lobito del Rio' (the Small River Wolf) this is the colloquial name for the giant water opossum (Chironectes minimis : Marsupialia) which occupies a sub-aquatic niche similar to that of the otter. 'El Lobo del Rio' (The River Wolf) this is the colloquial name given to the neotropical river otter (Lutra longicaudis) . 'Londra' refers to the Giant River Otter (Pteronura brasiliensis). Unfortunately these names are often used interchangeably and consequently considerable care has to be taken when attempting to determine presence/absence information from interview. Even the specimens purporting to be Giant Otters in the Zoological Gardens were in fact Lutra longicaudis. It is clear from analysis of tracks and signs, and interviews conducted with local poachers, hunters and campesinos that the Giant Otter (Pteronura brasiliensis) is a very rare visitor to the Amboro National Park. The interviews suggest that the animal occurred commonly in the Park up until 10 years ago, and was hunted for its pelt until 15 years ago. The species of otter which was commonly encountered was the neotropical river otter (Lutra longicaudis). This is a species complex whose taxonomy is not clearly understood, and since no attempt was made to capture otters in the present study, we are unclear of the precise species present in the Park.
Otters have not fared well in the presence of man, both species have been extensively hunted for their pelts. In recent years an even greater threat is posed by the dynamiting and poisoning of rivers and clearance of bankside vegetation. Amboro is a relatively new National Park and should be regarded as a showpiece for Bolivia. The foresight of the Government, C.D.F., Prodena Bolivia, and particularly Reginald Hardy and Robin Clarke in getting this venture off the ground and for their continuing support is commendable. Considerable problems remain however, paramount of which, is the hunting of animals for food, for live export or for skins. Ample evidence of this practise has been found on both visits to Amboro. As far as the otter populations are concerned, direct persecution is now minimal since there is no market for their skins. However the practise of fishing using dynamite or poison should be actively discouraged if the good populations of these animals are to be maintained.
Acknowledgements - We wish to thank the Vincent Wildlife Trust, Percy Sladden Trust, British Ecological Society, British & Foreign Schools Society, Gilchrlst Educational Trust, Rothley Trust, Whltley Anlmal Protection Trust, Durham University and the Mammal Society for financial assistance towards this project. We gratefully acknowledge the assistance provided by Robin Clarke (CDF), Reginald Hardy (Prodena Bolivia) and the University of Santa Cruz de la Sierra. Particular thanks are due to Joanna Copley. Kate Harrlson, Gill Hinchclif fe, Mark Ireland, Sarita Montes, Kate Watson and Darwin, Lucheo and Modesto for assistance with fieldwork.
Anderson, S. (1985). Lista preliminar
de mamiferos Bolivianos. Publ.Museo Nacional de historia natural.
Zoologia 3. La Paz
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