SEASONAL ECOLOGY OF INIA IN THREE RIVER BASINS OF SOUTH AMERICA (ORINOCO,AMAZON, AND UPPER MADEIRA) - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 35

Table 3 . Encounter rates of Inia in rivers of the Pacaya-Samiria Reserve, Peru.
S.S.D.W.R=significant seasonal differences within a river*.

River
(water type)

Season # surveys Mean

Inia /km

CV S.S.D.W.R

Marañón All 39 0.3 1.06 yes

(white) Falling 9 0.5 0.56 P = 0.01*

High 7 0.2 1.90

Low 4 0.4 1.40

Rising 19 0.1 1.90

Samiria All 11 1.5 1.92 no

section 1 Falling 4 0.7 0.75 P = 0.75

(mixed) High 3 0.6 0.12

Low 3 3.5 1.6

Rising 1 0.2 0

Samiria All 32 0.4 0.67 no

section 2 Falling 9 0.6 0.38 P = 0.16

(black) High 7 0.4 0.45

Low 5 0.5 0.74

Rising 11 0.3 0.97

Yanayaquillo All 25 0.4 1.65 no

(black) Falling 5 0.5 1.18 P = 0.92

High 7 0.4 1.23

Low 3 0.6 1.32

Rising 10 0.4 1.95

Atun Caño All 26 0.3 1.30 no

(black) Falling 4 0.3 1.10 P = 0.32

High 7 0.3 1.50

Low 5 0.1 2.10

Rising 10 0.4 1.05

Yanayacu All 15 1.1 1.00 yes

(mixed) Falling 0 x x P = 0.01*

High 5 0.3 1.23

Low 2 2.0 0.32

Rising 8 1.3 1.00

Pucate All 9 0.4 1.65 no

(black) Falling 1 0.4 1.42 P = 0.98

High 4 0.2 1.45

Low 1 0.3 1.40

Rising 3 0.6 1.83
* Single factor ANOVAS were used to compare means among seasons. When data were not normally
distributed, the Kruskal-Wallis test was used to compare sample medians.

Inia occurred in lakes as shallow as 1.5-m mean depth and in rivers as shallow as 2.4-m
mean depth (Table 4). There were significant seasonal differences in the mean and maximum
number of Inia in confluences (Table 5). Inia in confluences were seen most often during low
water, least often during high water, and in the largest aggregations during low water.
Inia sighting rates in Bolivia varied significantly among seasons (F = 80.55, df = 3,4, P =
0.0005; Figure 2). Sighting rates were greatest during the low water season (30.4% of the
total), and lowest during high water (21.5% of the total). Sampling effort did not vary by
season. In the rivers, dolphins were most often seen during falling and low waters (Figure 3).
In the oxbow lakes, dolphins were most often seen during rising and high waters. The number
of dolphins in the oxbow lakes declined during low water, sometimes to the point where they
were absent.