Pilcomayo River Research Articles

El Niño caused collapse of the sábalo fishery (Prochilodus lineatus, Pisces: Prochilodontidae) in a South American river.

El Niño is well known to affect marine fishery. The Southern Oscillation, however, may also have a strong effect on riverine fish production in flood-plains via its effect on river discharge. In years with high river discharges larger parts of the floodplain are innundated, increasing the surface area of suitable nursery grounds for young fish stock. In this way high river discharges are thought to have a positive effect on fish production, while low discharges are thought to have a negative effect. The collapse of the sábalo fishery in the Pilcomayo River in Bolivia, for instance, can be attributed to the 1990-1995 El Niño event and subsequent overexploitation of the fish stocks.

ENSO-controlled flooding in the Paran� River (1904?1991)

Since the poineering work of Walker [1, 2], evidence has been mounting that the E1Nifio-Southern Oscillation (ENSO) phenomenon causes rainfall anomalies in various parts of the globe [3, 4]. These anomalies are particularly well defined over the region of South America [4 6]. Rivers exhibit the advantage of being rainfall integrators over large areas. This approach was used by Richey et al. [7], who have shown a significant (5% level) coherent relationship in the crossspectral analysis of deseasonalized Amazon discharge data and atmospheric pressure anomalies at Port Darwin, Australia. Precipitation over the Amazon basin appears to be stimulated by the ascending motions associated with the Southern Oscillation (SO) positive phase and, hence, its positive level departures occur mainly during cold events, also known as La Nifia [31. Early in the study of the SO, a keen interest arose on the connection which might exist between the SO and the flow regime of the Paranfi River. Originally Mossman [8], and, a few years later, Bliss [9], pointed to the relationship of the SO with rainfall over southern Brazil, Paraguay, and northern Argentina, as presented by the level of the Paranfi River 420 km above the mouth, at Rosario, Argentina. In opposition to the Amazon, the Paranfi positive level departures are significantly correlated with ENSO warm extremes. Moreover, the "season" of ENSO-related precipitation in the Paranfi River drainage basin is in phase with the normal annual precipitation cycle [10], thus causing flooding events often disastrous during E1 Nifio years. To the best of our knowledge, the Paranfi is the largest river system in the world which exhibits such a behavior. A relatively long record of the Paranfi discharge oscillations is available for the Corrientes section (Fig. l). In analyzing this daily record (Fig. 2A), we seek to establish the frequency of the variability and the significance of the teleconnection with the ENSO phenomenon. This record reflects the hydrologic conditions prevailing over 1.95 x 106 km 2 (ca. 70o7o of the total basin area), including the runoff supplied by the Andean headwaters of the Bermejo and Pilcomayo rivers, the discharge provided by the Mato Grosso through the Paraguay River, and the water output delivered by the Upper Paranfi River basin with headwaters in Brazil's Serra dos Preneos. When the discharge time series of Fig. 2A is considered, the most outstanding features which arise are the pronounced seasonality with high waters in February/March and low waters in August/September the substantial variability, and the magnitude of the 1982/83 flood. This flood, obviously related to the strong 1982 E1 Nifio event, caused profound modifications in the biogeochemical functioning of the river [l l , 12]. Other large floods, such as those of 1904, 1911, 1932, and 1965, also occurred in accordance with ENSO warm events [4]. Worthy of attention are the negative deviations in the record (Fig. 2B), which persisted longer than positive ones, at least until

Ecology, status and conservation of the Red-fronted Macaw Ara rubrogenys

SummaryA five-month study of the Red-fronted Macaw Ara rubrogenys, endemic to Bolivia, yielded a population estimate of 2,000–4,000 individuals. The species is resident and locally common in, but restricted to, an area in the drainage systems of the Rio Grande, Rio Mizque and northern Rio Pilcomayo. One-third of the population was composed of juveniles some three months after the end of the breeding season. During the dry season, with food apparently short, more of the day was spent feeding than during the wet season. Semi-deciduous vegetation along the rivers produced fruits and seeds that sustained the macaws during the dry season, but the conversion of such areas to arable land forces the macaw to depend for some months on crops and weeds. Local farmers consider the macaw a serious pest on maize.

Bird Speciation in Subtropical South America in Relation to Forest Expansion and Retraction

AssTmAcr.-I analyzed two patterns of bird distribution in subtropical South America. The first was the disjunct distribution of pairs of species and subspecies between the southern Yungas and the Paranense forests, which are separated by 700 km of xerophytic Chaco woodland. Forest birds penetrate up to 200 km into the Chaco along gallery forests, but do not cross the rest of the Chaco, which constitutes an effective barrier. The second pattern involved several zones of secondary contact located in the Chaco lowland, where several woodland and grassland species and subspecies interact. I conclude that both bird-distribution patterns were produced by forest expansions along the Bermejo and Pilcomayo rivers that connected the southern Yungas to the Paranense region and interrupted the arid vegetation in the center of the Chaco. Vegetational fluctuations probably occurred several times during the Quaternary and produced phenotypic differentiation of sister taxa, both in the nowdisjunct forests and in the currently continuous Chaco. Received 26 June 1990, accepted 10 January 1992.

An assessment of the Prochilodus platensis Holmberg population in the Pilcomayo River fishery, Bolivia using scale-based and computer-assisted methods

. The catch from the fishery for the migratory Prochilodus platensis Holmberg on the Rio Pilcomayo shows considerable annual variation. Peaks were apparent in 1981 and 1982, followed by very low returns between 1983 and 1985 and a resurgence in 1986. The catch in 1986 was 1011t with the degree of annual variation probably lying between 500 and 2000t. In the Pilcomayo P. platensis is a rapidly growing short-lived fish with a maximum life expectancy of 6-7 years and an upper size approaching 61.5cm. The fish first migrate and appear in Bolivian’ waters when they are 21/2-3 years old, having spent the first 2 years on the nursery grounds, probably on the Argentine/Paraguay section of the river. Although fish of this age were numerous in the 1986 catches, the optimal market size is rather larger, and older fish are taken preferentially. The fishery actually depends upon very few age classes. A comparison of growth and mortality rates obtained from scale reading and from length frequency analysis by ELEFAN programs showed a close agreement. The considerable fluctuations in the fishery are largely due to the highly variable flood regime of the river rather than to fishing pressure, with the flood determining recruitment in 2 years’ time. Nevertheless, a combination of a sequence of poor flood years with sustained fishing pressure could seriously damage the fishery.

La passion amoureuse chez les Mataco: Kyutislí

This article, based on first-hand materials collected by the author during several field-periods in the Gran Chaco (1971-75), describes an institution ordering a certain type of relationship between men and women among the Mataco of the Pilcomayo river. The author shows how the concept of kyuihli, first used to qualify an institution, has other meanings. It means a certain state of personality as well as the the character imolved in this affair. The author examines its relationship with the prescribed forms of marriage and its sociological implications; kyutisli can be characterized more as a love-passion induced by the possession of an aját, a figure endowed with intention, appearance and will-power of its own, than a normal form of matrimonial relationship. Finally, the author shows the insertion of kyutisli in the cultural model specific of Mataco society.

The Mataco of Northern Argentina

When the first Spanish missionaries penetrated the Chaco early in the seventeenth century, they discovered a whole group of linguisticallyrelated tribes whose existence had gone unsuspected for a century. The most important of them, the Mataco, numbered about 30,000, and lived in numerous villages along the banks of the Bermejo, Paraguay, and Pilcomayo rivers. Pushed down off the Bolivian highlands by the more warlike Chiriguanos, the Mataco lived a peaceful, if primitive, life, hunting, fishing, and collecting carob pods, cactus figs, wild squash, and hearts of palm. During the eighteenth and nineteenth centuries, while Argentina exterminated most of her Indian population, the Mataco were left practically undisturbed; their lands were simply not valuable enough to be worth the white man's taking. Except for a few Anglican missions and an occasional trading post, the Chaco remained sealed off from the rest of Argentina.

Journeys and Explorations on the Pilcomayo River

Journeys and Explorations on the Pilcomayo River