Biology Reference
In-Depth Information
Table 7. Necropsies of Inia from Peru, Venezuela, and Bolivia, 1993-2000 field seasons
(McGuire 1995, Aliaga-Rossel 2000, McGuire 2002). Sex (F=female, M=male,
U=undetermined), and total length (T.L; snout to notch of tail) data are included. An X
indicates that a body was too decomposed to measure total length. Potential cause of
death comments are also included (P = poisoning, HT = Head trauma, Intra-specific
aggression = ISA, VS= Vessel-strike, & U = undetermined).
Date
Location
Sex *
T.L. (cm)
Season
(relative water level)
Comment
28-October-96
Peru
U
230.00
Low
P
28-October-96
Peru
U
217.05
Low
P
28-October-96
Peru
U
X
Low
P
29-October-96
Peru
U
232.50
Low
P
29-October-96
Peru
U
X
Low
P
29-October-96
Peru
U
X
Low
P
21-January-97
Peru
M
193.04
Rising
P
13-August-97
Peru
F
82.50
Low
HT
5-December-98
Peru
M
185.00
Rising
U
12-September-00
Peru
U
X
Falling
U
6-March-94
Venezuela
M
168.0
Low
U
4-September-98
Bolivia
M
200.0
Low
ISA
9-July-99
Bolivia
M
215.0
Falling
VS
Strandings
Stranded dolphins were not observed in any of the study areas. In Bolivia, live Inia were
observed in an oxbow lake that had been isolated from the main river channel during extreme
low water. During the extreme low water season in Bolivia and Venezuela, Inia were
observed to transit between water bodies via very shallow channels (0.5 m depth), but they
always appeared to move quickly and gave the impression of increased wariness as they did
so.
Intra-Specific Aggression
Although tooth-rake marks believed to be made from con-specifics were often seen on
live Inia in all three study areas, in Peru and Venezuela none of the necropsied Inia (Table 7)
had tooth-rake marks on the body that might have indicated aggression from other dolphins.
During extreme low water in Venezuela, an adult Inia (sex undetermined) was observed
for approximately ten hours as it appeared to try to maintain its position in very shallow water
(0.25-0.5 m) along a sandy beach, while as many as five adult dolphins patrolled the deeper
water nearby, occasionally approaching the beached dolphin as singles, pairs, and trios, and
biting, prodding, and grabbing it by the tail in apparent attempts to drive or drag it to deeper
water. The beached dolphin vigorously resisted these efforts, and active bouts of snorting,
chuffing, tail slapping, pectoral fin slapping, and thrashing occurred throughout the day. This
dolphin was not seen in the study area again (McGuire, 1995).
A dead Inia encountered during the low water season in Bolivia may have died as a result
of intra-specific aggression. One day before the carcass was discovered, reproductive activity
among approximately 12 Inia was observed along a sandy beach at a confluence. There was a
great deal of splashing, chasing, snorting/chuffing, and contact between the dolphins. This
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