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

1998, coincident with the introduction of loud underwater
acoustic deterrent devices intended to keep pinnipeds away
from salmon-culture pens (Morton 2000).
Dusky dolphin, Lagenorhynchus
obscurus
Dusky dolphins have a disjunct distribution in the cold
temperate Southern Hemisphere (IWC 1997a; Brownell and
Cipriano 1999). Their presence near Tasmania and southern
Australia, long supposed, was only recently confirmed (Gill
et al. 2000). Populations centered in New Zealand, the west
coast of South America, and south-western Africa are genetically
distinct and may deserve at least subspecies status
(Würsig et al. 1997). There is also a hiatus in their distribution
spanning about 1000km along the Chilean coast, and
the animals off Patagonia are smaller than those off northern
Chile and Peru, suggesting that the populations in western
and eastern South America are separate (Figure 20). It
remains uncertain whether the groups around oceanic
islands in the western South Pacific (Campbell, Auckland,
and Chatham), South Atlantic (Gough and the Falklands),
and Indian Ocean (Amsterdam, Prince Edward, and St.
Paul) are discrete or regularly mix with animals in other
areas.
Dusky dolphins are found in large schools and are generally
considered abundant. However, recent catches off
Peru, consisting mainly of gillnet entanglement but with the
addition of illegal harpooning, have been large enough to
cause serious concern (Van Waerebeek 1994; Van
Waerebeek et al. 1997, 1999b, 2002). Changes in the catch
composition suggest that the regional population of dusky
dolphins is depleted. A growing concern in Peru is the
demand for dolphin meat and blubber to be used as shark
bait (Van Waerebeek et al. 1999b).
Figure 20. A dusky dolphin breaching high above the
surface in Golfo Nuevo, Patagonia, Argentina, November
1999. Photo: Mariano Coscarella.
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Incidental mortality in mid-water trawls off Patagonia in
the mid-1980s was estimated at 400–600 dolphins per year,
primarily females, declining to 70–215 in the mid-1990s
(Dans et al. 1997). At least 7000 dusky dolphins were
present along a portion of the Patagonian coast in the mid-
1990s (Schiavini et al. 1999). Several hundred continue to
die each year in various types of fishing gear off Argentina
(Crespo et al. 2000). Some animals are also taken in beach
seines and purse seines and by harpooning off South Africa,
but the number is not thought to be large. The estimated
annual incidental kill of dusky dolphins in fishing gear
around New Zealand was within the range of 50–150 during
the mid-1980s (Würsig et al. 1997).
Northern right whale dolphin,
Lissodelphis borealis
The northern right whale dolphin is widely distributed
across the cool temperate North Pacific. It was subject to
very high incidental mortality in pelagic driftnet fisheries
for squid from the late 1970s through the 1980s. Estimated
annual kills in the low to mid tens of thousands were almost
certainly large enough to cause at least local or regional
stock depletion (Mangel 1993; Yatsu et al. 1994). The UN
moratorium on large-scale high-seas driftnets that came into
effect in 1993 relieved this pressure to a considerable extent,
but the continued use of gillnets to catch billfish, sharks,
squid, and tuna inside the exclusive economic zones (EEZ)
of North Pacific countries results in the killing of hundreds
of right whale dolphins each year. These dolphins have not
been exploited directly on a significant scale anywhere in
their range although they are sometimes taken in the harpoon
fishery for Dall’s porpoises in northern Japan
(Miyazaki 1983). There are about 14,000 northern right
whale dolphins off the west coast of the United States
(Carretta et al. 2001).
Southern right whale dolphin,
Lissodelphis peronii
This oceanic species has a circumpolar range in cool temperate
waters of the Southern Ocean, mainly between the
Subtropical and Antarctic convergences (Newcomer et al.
1996). No abundance estimates are available, but these
dolphins occur in large schools and can be common in
productive areas. Although they are killed occasionally in
fishing gear, no large-scale incidental mortality has been
documented. However, there is concern that large numbers
are being killed in the driftnet fishery for swordfish (Xiphias
gladius) that began in northern Chile in the early 1980s
(Reyes and Oporto 1994). The lesson from the North Pacific
(see above), where high-seas driftnet fishing caused massive
mortality of northern right whale dolphins, is that
southern right whale dolphins would be vulnerable to any
large-scale deployment of gillnets within their offshore
range (cf. Peddemors 1999).