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

may have concentrations of these dolphins (Jefferson 2000).
A population of at least 450 dolphins inhabits Algoa Bay on
the eastern cape of South Africa (Karczmarski et al. 1999).
Anti-shark nets off Kwazulu-Natal, South Africa, and
Queensland, Australia, kill hump-backed dolphins (and
other cetaceans) in numbers that are high relative to estimated
abundance (Cockcroft 1990; Paterson 1990;
Corkeron et al. 1997). Entanglements in gillnets have been
recorded across the rim of the Indian Ocean (Ross et al.
1994; Jefferson and Karczmarski 2001). The greatest direct
source of human-caused dolphin mortality in Hong Kong
appears to be from incidental catches in fishing gear (most
likely pair trawls) and vessel collisions (Jefferson 2000).
Organochlorines, especially DDTs, may be compromising
the health of populations in at least southern China and the
Bay of Bengal (Tanabe et al. 1993; Parsons and Chan 1998).
Mercury levels are exceptionally high in Hong Kong
dolphins (Jefferson 2000).
Atlantic hump-backed dolphin, Sousa
teuszii
The Atlantic hump-backed dolphin is endemic to the eastern
tropical Atlantic, where it is limited to coastal and inshore
waters. Highest densities are in brackish, mangrove-lined
estuaries. The species appears to exist as a series of local
communities with little interchange, although this hypothesis
needs testing with genetic and other evidence. There
is much concern about the species’ conservation status.
Although no abundance estimates are available, it has become
rare in at least two areas where it used to be common.
These are the coastal waters of Senegal and the Gambia
(Van Waerebeek et al. 2000) and the shallow waters of
upper Dakhla Bay, Morocco/ex-Western Sahara
(Notarbartolo di Sciara et al. 1998). In both cases, the very
high intensity of fishing is viewed as a threat to humpbacked
dolphins because of both entanglement in fishing
gear and reduced prey availability. These dolphins are a
high priority for research and conservation because of their
restricted range, narrow ecological niche, generally low
abundance, and continuing threats (IWC in press).
Pantropical spotted dolphin, Stenella
attenuata
This abundant and very widely distributed species is, as the
name implies, pantropical. It inhabits both near-shore and
oceanic habitats in tropical and warm temperate seas. Three
subspecies are currently recognized in the Pacific Ocean,
where large samples have been available for study as a result
of mortality in the tuna purse seine fishery. These are an
unnamed Hawaiian race, an unnamed eastern Pacific offshore
race, and an eastern Pacific coastal race (S. a.
graffmani) (Rice 1998). Offshore spotted dolphins bore the
brunt of the massive dolphin kill by tuna seiners from the
late 1950s to the 1980s. For example, in the period 1959 to
1972, nearly five million dolphins were killed, and of this
number, about three million were from the north-eastern
offshore stock of spotted dolphins (Wade 1995). Although
mortality rates have been greatly reduced, a recent assessment
of this population indicated that it was not recovering
at the expected rate and that the stress of being chased and
captured repeatedly in the tuna nets, separation of mothers
from young, and under-reporting of fishery kills could account
for the depressed growth rate (Southwest Fisheries
Science Center 1999). Abundance estimates based on surveys
in the late 1980s totaled about two million spotted
dolphins in the eastern tropical Pacific (Wade and
Gerrodette 1993). In 1998, the north-eastern offshore stock
was estimated at about 600,000–1,000,000 and the coastal
stock at about 70,000–100,000 (T. Gerrodette, pers.
comm.).
Pantropical spotted dolphins are subject to high mortality
in some other parts of the world, notably Japan, where they
are killed by harpooning and driving. Catches in Japan have
been in the thousands in some years (Kishiro and Kasuya
1993), although they have totaled less than 500 per year over
the past decade (see summary tables in Journal of Cetacean
Research and Management annual supplements). Estimated
abundance in Japanese waters was about 440,000 in the
early 1990s (Miyashita 1993). Other areas where large numbers
of spotted dolphins have been killed for food or bait
include the Solomon Islands, Sri Lanka, Lesser Antilles,
Indonesia, and the Philippines. Although the species is not
considered threatened, there is a need for improved understanding
of regional stock differences, abundance, and take
levels.
Clymene dolphin, Stenella clymene
This species occurs in deep tropical and subtropical Atlantic
waters, including the Gulf of Mexico and the Caribbean Sea
but not the Mediterranean. It is not considered abundant
anywhere. There are an estimated 5000–6000 clymene dolphins
in the northern Gulf of Mexico (Waring et al. 2001).
Clymene dolphins are harpooned at least occasionally by
fishermen in the Lesser Antilles, and they are sometimes
caught in fishing gear elsewhere. The only area in which a
significant bycatch is thought to occur is in the eastern
tropical Atlantic, where, according to unconfirmed sources,
significant numbers may be taken in tuna purse seines (T.
Jefferson, pers. comm.). This situation merits closer investigation
(Chapter 5, Project 44).
Striped dolphin, Stenella coeruleoalba
The striped dolphin is cosmopolitan in tropical and temperate
waters. It is generally abundant, but some populations
are in serious trouble. The most important of these
are in the western North Pacific and the Mediterranean
Sea. Catches of striped dolphins in Japan have declined
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