Biology Reference
In-Depth Information
activity continued throughout the night, accompanied by abnormally loud exhalations and
labored breathing by at least one dolphin. The following morning, the body of a freshly-dead
adult male Inia was encountered on the beach. Its pectoral and caudal fins displayed
numerous deep tooth scars from other Inia (determined by scar depth, shape, and spacing),
bleeding from the anal slit (from internal hemorrhaging), and heavy bruises and swelling
around the blowhole (Aliaga-Rossel, 2000).
Vessel Strikes
In Venezuela, vessel strikes of Inia were not observed, nor were any dead Inia
encountered that appeared to have been victims of vessels strikes. Two photo-identified Inia
in Peru had deep dorsal scars that may have been caused by boat propellers, and a third
dolphin had a broken upper beak that might have resulted from a boat strike. A dead dolphin
encountered during rising water in Bolivia appeared to have been struck by an outboard
motor, as the left side of the beak was heavily cut and the lower left jaw was broken (Aliaga-
Rossel, 2000).
Interactions with Fisheries
Aliaga-Rossel (2000, 2002) reported that the major threat to Inia in Bolivia's Mamor←
River Basin is entanglement in nets during fishing operations, especially during low water
when fishing effort by humans is greatest. Interviews with fishermen indicated that the season
of greatest fishing success is between May and September (period of falling and low water).
During this time, the fishermen place their nets at the mouths of the lagoons and tributaries in
order to catch fish heading for the main river, and they frequently encounter dolphins trapped
in their nets. They are more likely to trap the younger dolphins, as perhaps these animals are
the least experienced with nets and the most curious. Dolphins may be released alive by
fishermen, but often they are left to die, or are killed with machetes. The fishermen may use
dolphin meat as bait to attract fish, or use the oil to cure lung ailments. Local people report
that during one year in the Bolivian study area, six dolphins died in fishing nets; of these, two
calves, one juvenile, and one adult were captured between May to September, which
correspond to the seasons of falling and low water. The nets were located across the mouth of
a lagoon.
The major threats to river dolphins in Peru have been reported as entanglement in fishing
gear (especially gill nets), and also capture in drop traps designed to catch paiche fish
( Arapaima gigas ) and manatees ( Trichechus inunguis ; Leatherwood, 1996). A local
fisherman estimated that as many as 50 dolphins a year were being killed in nets or drop traps
in the oxbow lake Tipishca del Samiria (Leatherwood, 1996), although Zúñiga (1999)
conducted almost daily surveys of this lake for nearly a year and did not encounter fishery-
related dolphin mortalities. Taboos that prevented the intentional harm of river dolphins once
existed among the native people of the region (Best & da Silva, 1989; Slater 1994), but such
beliefs are disappearing in some places, and more recent settlers often regard the dolphins as
competitors for fish (Leatherwood, 1996; Reeves et al., 1999). On occasion, dolphins are
deliberately killed by fishermen attempting to protect their nets or reduce the dolphins' take
of fish (Leatherwood, 1996; Reeves et al., 1999; McGuire 2002).
Of the ten dead Inia encountered in Peru between 1996 and 2000, seven were
encountered during low water, two during rising water, and one during falling water (Table
7). Of the seven dead Inia encountered during low water, six were believed to have died from
Search WWH ::




Custom Search