Biology Reference
In-Depth Information
M
ETHODS
Study Areas
River dolphin surveys were conducted in freshwaters of Venezuela, Peru, and Bolivia
between 1993 - 2001 (Figure 1; Table 1). All three study areas contained main stem rivers,
tributaries, confluences, and oxbow lakes (i.e., former river channels than may become
seasonally isolated from the main channel), and contained whitewater and blackwater habitats
(differentiated by turbidity, nutrient load, pH, and origin; Sioli, 1984). Four seasons were
assigned according to relative water levels: high water, falling water, low water, and rising
water. Seasons were not correlated to month of the year as this differed among study areas.
Water levels of Neotropical river systems are influenced by local rains, snowmelt from the
Andes, and water levels both up- and downstream. The Peruvian study area is classified as
lowland tropical rainforest, whereas the Bolivian and Venezuelan study areas are
characterized as tropical savannas with gallery forests (Cox & Moore, 1993).
The Venezuelan study area along the Cinaruco River is 3 km
2
in area and contains 20 km
of water courses. This area lies within the Santos Luzardo National Park. The blackwater
Cinaruco River flows east to the Orinoco River across the llanos (lowland plains) of Apure
state. The lower portion of the Cinaruco River is particularly sinuous and forms a complex
flood plain with numerous channels and oxbow lakes. The river floods the surrounding plains
from May-November, then returns to the main channel during the dry season (usually
February-April).
The Peruvian study area is located within Peru's Pacaya-Samiria Reserve, 93 km upriver
from the city of Iquitos, Department of Loreto, in the far western Amazon Basin. The Reserve
is bounded by the Marañón and Ucayali rivers, which are the parent rivers of the Amazon
River. Major tributaries of these rivers are, respectively, the Samiria River (400 km long), and
the Pacaya River (380 km long). The Reserve has over 10,000 km of linear waterways
(blackwater, whitewater, and mixed), comprised of main stem rivers, tributaries, confluences,
channels, and lakes. A protected area since 1940, the Pacaya-Samiria Reserve is the largest
reserve in Peru at 2,150,700 ha (INRENA-CTARL, 2000). Water levels are usually lowest
during September, although this varies yearly. Water levels can fluctuate greatly during the
overall rise between October and May, and peak waters generally occur in May or June.
The Bolivian study area is located along the Tijamuchi River, Moxos province,
Department of Beni, and contains 185 linear km of waterways, upriver from and including the
confluence of the Tijamuchi and Mamoré rivers. Three oxbox lakes adjoining the Tijamuchi
were also surveyed. Highest water levels occur between December and April, and lowest
water levels are generally from June to October. The lower Tijamuchi is a mixed white- and
blackwater river.
Field Sampling
Data collection consisted of boat-based surveys of dolphins and habitat, photo-
identification of individual dolphins, necropsies of dolphins, and interviews with local people.
Environmental surveys consisted of measurements of water depth, channel width, water
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