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 34

Literature Review

We reviewed the published and unpublished literature about the seasonal ecology of Inia ;
the unpublished literature consisted of project reports, bachelor and master theses, doctoral
dissertations, and conference abstracts.

R ESULTS

Distribution

In Venezuela, Inia sighting rates throughout the study area were significantly associated
with season (χ 2 = 48.65, df = 2, P = 0.001, N = 489) and dolphins were observed most often
during the falling water season and least often during rising water (Figure 2). Sighting rates
varied seasonally within oxbow lake and river habitats (χ 2 = 52.09, df = 2, P = 0.001, N = 258
and χ 2 = 10.21, df = 2, P = 0.006, N = 63, respectively). Sighting rates within lakes were
greatest during falling water, then declined during low and rising water. Fewer dolphins were
seen in rivers during falling water than during any other season. Sighting rates in confluences
were not associated with season (χ 2 = 0.470, df = 2, P = 0.79, N=156).
Inia sighting rates in Peru did not differ significantly according to season in two of the
three surveyed lakes (Table 2), or four of the six surveyed rivers (Table 3), as the variation in
sighting rates was greater within-seasons than among-seasons. When all sightings were
pooled across all lakes, rivers, and confluences surveyed and standardized for survey effort,
sighting rates were greatest during low water and lowest during rising water (Figure 2).
Table 2 . Seasonal Inia abundance in lakes of the Pacaya-Samiria Reserve, Peru.
SSDWL (significant seasonal differences within a lake*).

Lake Season # transects Mean

Inia /km

CV SSDWL

San Pablo All 25 10.9

(0.7 Inia /km 2 )

0.73 Yes

P = 0.02*

Falling 5 7.2 1.28

High 3 17.3 0.35

Low 4 1.0 0.82

Rising 13 13.5 0.41

Atun Cocha All 23 9.2

(1.5 Inia /km 2 )

0.79 No

P=0.43

Falling 3 7.7 1.04

High 3 9.7 0.43

Low 6 5.5 1.55

Rising 11 11.6 0.59

Tipishca del All 29 50.7

(3.5 Inia /km 2 )

0.45 No

P= 0.84 Samiria

Falling 5 57.6 0.44

High 7 45.9 0.32

Low 5 53.6 0.56

Rising 12 49.4 0.49
* 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.