Biology Reference
In-Depth Information
During boat-based surveys in rivers, tributaries, lakes, and confluences (for detailed
methods see McGuire, 1995; Aliaga-Rossel, 2000; McGuire, 2002) group size, age
composition and GPS position were recorded for each dolphin sighting and results were used
to determine encounter rates. Age classifications of
Inia
were based on visual estimation of
total body length and divided into two categories:
neonates
(<1 m), and
other
(>1 m).
Neonates were further identified by their uncoordinated swimming and surfacing behavior,
and fetal folds (when possible). The
other
category included older calves, juveniles,
subadults, and adults, and was not further subdivided as it was often difficult to visually
differentiate size-class of intermediate sized animals. Age, sexual maturity, and sex are not
clearly differentiated based on length alone in these dolphins (da Silva, 1994). Mating
behavior and intra-specific aggression were opportunistically recorded. An interaction was
categorized as mating if ventral to ventral contact between two or more dolphins was
observed.
Fishing activity by humans was noted opportunistically in Venezuela and Bolivia, and
was systematically recorded during dolphin surveys in Peru's lake San Pablo de Tipishca in
2000. Observers counted and recorded the position of all fishing nets (seines and gill nets),
temporary fishing camps, and fish cages. Fishing nets were counted regardless of if they were
deployed or in canoes. Fish cages were used to hold live fish that had been caught in nets.
In Venezuela, potential prey fish were collected with seines and an experimental gill net
(see McGuire & Winemiller, 1998 for details), and catch per unit effort (CPUE) was
calculated by dividing the total number of fishes caught by either the total number of meters
the seine was pulled or by the total number of minutes the gill net was in the water.
Rates of Travel
Rates of travel were calculated for individual dolphins seen in multiple times during the
course of a survey trip (which was typically 7-12 days in Bolivia and Peru, and 6 months in
Venezuela). Photo-identification techniques were used to identify individual
Inia
by cuts and
nicks to the dorsal fin and back, pigmentation patterns on the back and head, scars, tooth-rake
marks, and abnormally shaped beaks (McGuire, 1995; Aliaga-Rossel, 2000; McGuire, 2002;
McGuire & Henningsen 2007). Photo-identification results from Peru were supplemented by
photo-catalogs from the same area assembled by Leatherwood (1996), Henningsen (1998),
and Zúñiga (1999), and range maps and sighting histories were created from the compiled
data, which spanned the period 1991-2000.
Mortality
All dead dolphins encountered were examined for length, girth, body condition, sex,
stomach contents, pregnancy and/or lactation in females, tooth eruption of neonates and
calves, and possible signs of death.
Search WWH ::
Custom Search