Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN
Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN
Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN
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Irrawaddy dolphin, Orcaella<br />
brevirostris<br />
Irrawaddy dolphins are patchily distributed in shallow,<br />
near-shore tropical <strong>and</strong> subtropical marine waters of the<br />
Indo-Pacific, from northern Australia in the south, north to<br />
the Philippines (Dolar et al. <strong>2002</strong>) <strong>and</strong> west to north-eastern<br />
India (Stacey <strong>and</strong> Leatherwood 1997; Stacey <strong>and</strong> Arnold<br />
1999). Their distribution is centered in estuaries <strong>and</strong> mangrove<br />
areas. Freshwater populations occur in three river<br />
systems; the Mahakam of Indonesia, the Ayeyarwady<br />
(formerly Irrawaddy) of Myanmar (formerly Burma), <strong>and</strong><br />
the Mekong of Laos, Cambodia, <strong>and</strong> Vietnam. Irrawaddy<br />
dolphins also occur in completely or partially isolated<br />
brackish water bodies, including Chilka Lake in India <strong>and</strong><br />
Songkhla Lake in Thail<strong>and</strong>. The animals in northern<br />
Australian waters are morphologically distinct from those in<br />
Asia (Beasley et al. <strong>2002</strong>a).<br />
The distribution of Irrawaddy dolphins overlaps areas of<br />
intensive use by humans. For example, in the Mekong delta,<br />
rows of netting stretch across many channels, providing a<br />
likely explanation for the lack of recent dolphin sightings in<br />
the area even though several skulls are preserved in local<br />
“whale temples” (Smith et al. 1997a). The species apparently<br />
has been seriously depleted in parts of Thail<strong>and</strong><br />
(Andersen <strong>and</strong> Kinze in IWC 1994a, p.110). Incidental<br />
mortality in fisheries (e.g., gillnets, explosives) is likely the<br />
principal cause of depletion, although the degradation of<br />
river <strong>and</strong> lake systems caused by damming, forestry<br />
practices, <strong>and</strong> mining could also play an important role<br />
(Baird <strong>and</strong> Mounsouphom 1997; Smith et al. 1997b; Kreb<br />
1999; Smith <strong>and</strong> Hobbs <strong>2002</strong>). Live-capture for captive<br />
display poses an additional pressure on small, localized<br />
populations such as those in the Mahakam River <strong>and</strong> possibly<br />
the Ayeyarwady River. In Australia, Irrawaddy dolphins<br />
are killed in anti-shark nets <strong>and</strong> gillnets (Parra et al.<br />
<strong>2002</strong>).<br />
Recent surveys indicate dramatic declines in range <strong>and</strong><br />
abundance of the Mekong <strong>and</strong> Mahakam freshwater populations<br />
(IWC 2001a). The latter was classified as Critically<br />
Endangered in the Red List in 2000 after surveys found only<br />
a few tens of dolphins, confined to an approximately 300km<br />
segment of river (Kreb 1999, <strong>2002</strong>). Another small group of<br />
animals living at the head of Malampaya Sound in Palawan,<br />
Philippines, appears to be geographically isolated (Dolar et<br />
al. <strong>2002</strong>). If this proves to be the case, the Malampaya<br />
population should also be classified as Critically Endangered<br />
simply by virtue of its low numbers. Surveys in<br />
2001 resulted in an estimate of 77 individuals (CV 27.4%)<br />
confined to a 133km 2 area of the inner sound (B.D. Smith,<br />
unpublished data).<br />
Killer whale or Orca, Orcinus orca<br />
The killer whale has a cosmopolitan distribution, but there is<br />
much geographical variation in its morphology, behavior,<br />
43<br />
<strong>and</strong> ecology (Dahlheim <strong>and</strong> Heyning 1999). Further<br />
research may justify recognition of more than one species<br />
(Rice 1998; Baird 2000). Although killer whales are fairly<br />
abundant <strong>and</strong> widespread on a global scale, regional populations<br />
can be small <strong>and</strong> highly specialized, <strong>and</strong> therefore<br />
vulnerable to over-exploitation <strong>and</strong> habitat deterioration.<br />
Killer whales are large enough to represent good value for<br />
effort in whaling operations; they are available in many<br />
coastal areas; <strong>and</strong> their predatory habits mean that “predator<br />
control” is an added incentive for killing them (even though<br />
there is no evidence that such culling actually enhances fish<br />
stocks). Hunting of killer whales is not conducted on a large<br />
scale at present, but considerable numbers were killed until<br />
the early 1980s in the North Atlantic by Norwegian whalers,<br />
in the western North Pacific by Japanese whalers, <strong>and</strong> in the<br />
Antarctic by the Soviet whaling fleet. Small numbers are<br />
still killed in coastal whaling operations in Japan, Indonesia,<br />
the Lesser Antilles, <strong>and</strong> Greenl<strong>and</strong>. Their place at the top of<br />
marine food webs means that killer whales come into conflict<br />
with humans in unique ways. One recent example<br />
comes from the Aleutian Isl<strong>and</strong>s in the North Pacific, where<br />
killer whale predation has been proposed as a major factor in<br />
the rapid decline of sea otters. According to this hypothesis,<br />
human overfishing of forage fishes reduced the carrying<br />
capacity for seals <strong>and</strong> sea lions, the traditional prey of<br />
certain pods of killer whales, forcing the whales to increase<br />
their predation on otters. With declines in otter densities, sea<br />
urchin populations were released from predation, allowing<br />
them to increase <strong>and</strong> cause deforestation of near-shore kelp<br />
beds (Estes et al. 1998). Another well-established <strong>and</strong> growing<br />
concern is depredation by killer whales (<strong>and</strong> other<br />
species such as false killer whales <strong>and</strong> sperm whales) on<br />
commercial longlines. Such interactions result in direct retaliation<br />
by fishermen <strong>and</strong> calls for organized control<br />
measures.<br />
Their popularity as display animals creates a strong dem<strong>and</strong><br />
for live killer whales to be brought into captivity.<br />
However, few have been removed from the wild in recent<br />
years. Anti-captivity campaigns, along with limited success<br />
at captive breeding, have reduced the pressure on wild<br />
populations to supply oceanaria. One inshore population of<br />
killer whales in British Columbia <strong>and</strong> Washington has declined<br />
in recent years (Ford et al. 2000), prompting concern<br />
about the exceptionally high levels of contaminants found in<br />
their tissues (Ross et al. 2000) <strong>and</strong> the possibility that they<br />
are suffering from the depletion of local salmon stocks (their<br />
preferred prey) or the disturbance caused by ship <strong>and</strong> boat<br />
traffic (Baird 2000).<br />
Melon-headed whale, Peponocephala<br />
electra<br />
This poorly known species is distributed in deep oceanic<br />
waters at tropical <strong>and</strong> subtropical latitudes worldwide<br />
(Jefferson <strong>and</strong> Barros 1997). Abundance estimates indicate