Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN

Figure 7. Commerson’s dolphins on the bow of an
inflatable boat during studies of the effects of such
interactions on the animals. Bahia Engaño, Patagonia,
Argentina, near the northern limit of the species’ range,
1999. Photo: Mariano Coscarella.
trips to see dusky and Commerson’s dolphins
(Lagenorhynchus obscurus and Cephalorhynchus commersonii,
respectively) off northern Patagonia (Argentina)
(Figure 7) and Peale’s dolphins (Lagenorhynchus australis)
near Punta Arenas (Chile), but neither country has any laws to
regulate this activity and limit its impact on the animals
(Crespo, unpublished data). Whale-watching centered on
southern right whales has flourished for the last 30 years in
coastal Patagonia, where it has become the most important
local tourist attraction (Rivarola et al. 2001). Incipient whalewatching
industries along the Spanish Mediterranean coast
and near the large tourism centers in south-eastern and north-
eastern Brazil are expected to develop rapidly in
coming years. Although there is little evidence to
indicate that whale-watching has had negative
effects on cetacean populations (IFAW, Tethys
Research Institute and Europe Conservation 1995),
one of the priorities of the IWC Scientific
Committee’s Sub-committee on Whale-watching
is to examine the short- and long-term effects of
tourism on cetacean populations and to develop
general principles for minimizing these (IWC
1999a et seq.).
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2.2 Habitat loss and degradation
Historically, the problem of habitat loss and degradation has
probably been less severe or acute for cetaceans than for
many terrestrial taxa. Nevertheless, it has become a serious
issue for marine mammals in recent decades, especially for
freshwater and coastal species (Harwood 2001). Water development
projects in Asia, and to a lesser degree South
America, have fragmented cetacean populations and, in
some areas, eliminated their habitat (Reeves and Smith
1999; papers in Reeves et al. 2000b). Little is known about
what characteristics make a particular river reach suitable
for cetaceans, or about the specific ways in which vessel
traffic, riverbank development, dams, and entrainment
structures (e.g., groynes and embankments) affect these
animals (Smith et al. 1998)( Figure 8). From what is known
about the habitat requirements of cetaceans in running
waters, they benefit from the refuge provided by complex
physical features that interrupt strong current flows (e.g.,
bends and confluences). These features are often severely
degraded by dams and embankments, with the waterways
being transformed into biologically impoverished, canallike
systems (Smith and Reeves 2000b). Another potentially
catastrophic problem is the upstream abstraction of water
from river systems inhabited by cetaceans. Reduced water
supplies have already caused range declines in Endangered
South Asian river dolphin populations, and this trend is
bound to continue as human populations expand and increase
their consumption of water.
Appropriation of space by harbor construction, land
“reclamation,” and mariculture has similarly reduced the
available habitat of coastal marine cetaceans. Even though
cetaceans may occur in heavily used harbors and be seen
regularly in the vicinity of “fish farms” (Figure 9), their
health may be at risk. For example, in British Columbia
Figure 8. Embankments constructed for questionable flood-control
benefits degrade the features that make Asian rivers suitable for
supporting freshwater cetaceans and eliminate access to essential
habitat for floodplain-dependent fishes and crustaceans.
Photo: Brian D. Smith.