Orinoco Wetlands

The endangered giant otter has a heavily fragmented distribution in the Orinoco Wetlands ecoregion between Venezuela and Argentina. Naturally these otters require large river and wetland habitats, and the river system is essential to connect their disjunct populations. 

Aptly named, giant otters can reach up to 1.8 m in length. They are highly social and live in family groups of up to 20 individuals, using a wide variety of sounds to communicate, and even playing and hunting together. Because their survival depends on healthy fish populations, their absence can be a sign of overfishing and an indicator of diminished river ecosystem health. Each otter has a unique patterns of white and brown fur on the neck which makes it possible to tell individuals apart.

The Orinoco Wetlands are flooded grasslands occurring in seven distinct patches, embedded in a matrix of mangroves, swamp forest, moist forest, and llanos savannas. The ecoregion is located to the north of the Orinoco River Delta, the second largest river in the Neotropics, in eastern Venezuela. Climate in this region is tropical and wet. Precipitation varies throughout the year between 1,000 and 2,000 mm. Elevations typically average 1 m but reach as high as 9 m in the levies along the coast. 

The soils in this ecoregion are almost entirely alluvial deposits, originating as far as the northern Andes of Colombia and Venezuela. The core of this ecoregion is considered tropical tall flooded grasslands. Interspersed among the grasses are local concentrations of palms such as Manicaria, taparo, Trithrinax spp., and Atilla spp. In certain areas of the savanna the moriche palm dominates. Over 100 species of aquatic vascular plants, as well as grasses and sedges, have been recorded in the wetlands.

Floodplains of large rivers, such as the Orinoco, are among the most productive ecosystems. Little research has been conducted in the wetlands of the Orinoco Delta and species compositions are predominately influenced by the surrounding moist forests, swamp forests, and mangroves. The moriche palm provides food to a number of animal species, including numerous primates, parrots, and rodents, and nesting habitat for many bird species. Species of special interest within this ecoregion are the Orinoco crocodile (critically endangered), Amazon river dolphin, jaguar, bush dog, giant otter, Orinoco goose, and harpy eagle. 

The delta region of the Orinoco River has been declared an internationally significant wetland and is extremely sensitive to ecological damages. Although still in moderate ecological condition, the number and severity of environmental threats have increased in recent years. The majority of this ecoregion is represented and protected in national parks, indigenous areas, and biosphere reserves, which offer varying degrees of protection. The Delta del Orinoco Biosphere Reserve was established in 1991 and is the largest protected area within the delta region. Other protected areas of note include Delta del Orinoco National Park, Turuïpano National Park, and Mariusa National Park. 

There are a multitude of threats within the ecoregion. On a large scale, oil extraction and exploration, water diversion projects, and dam/dike construction upstream are of immediate concern. Human population pressure increasingly threaten the sustainability of delta fisheries, potentially leading to overfishing in areas close to towns, villages, and along rivers. 

The floodplains of large rivers are among the first to be altered by economic development and population growth because of their high productivity. Portions of this wetland ecoregion have been severely altered due to a flood control program initiated in the 1960s. The reduction of seasonal flooding intended for the land to be more suitable for cattle farming. 

Consequently, the reduced water levels in the upper delta have caused the region to become tidal, and as a result the water levels now rise and fall by 1–2 m daily. This has also caused the salinity to increase dramatically, and in turn has impacted the flora and fauna.

The priority conservation actions for the next decade are to: 1) design sustainable fishery programs to compensate for increasing population; 2) restrict alteration of floodplain habitats; and 3) provide alternative economic sources that detract from water diversion projects for agriculture and cattle farming.

Citations 

1. Schipper, J. 2018. Northern South America: Northeastern Venezuela. https://www.worldwildlife.org/ecoregions/nt0906 Accessed September 12, 2018
2. Dinerstein, E., D. M. Olson, D. L. Graham, A. L. Webster, S. A. Primm, M. P. Bookbinder, and G. Ledec. 1995. A conservation assessment of the terrestrial ecoregions of Latin America and the Caribbean. DC.: WWF and The World Bank.
3. Lewis, Jr.W. M., S. K. Hamilton, M. A. Lasi, M. Rodríguez, and J. F. Saunders III. 2000. Ecological Determinism on the Orinoco Floodplain. BioScience, Vol. 50 No. 6. P. 681-692.
4. Groenendijk, J., Duplaix, N., Marmontel, M., Van Damme, P. & Schenck, C. 2015. Pteronura brasiliensis. The IUCN Red List of Threatened Species 2015: e.T18711A21938411 http://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T18711A21938411.en. Accessed September 12, 2018