Lagenorhynchus obscurus

Dusky Dolphin

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Dusky Dolphin



The dusky dolphin is a highly social species, sometimes found in herds of over 1,000 individuals, although groups of 20 to 500 are more common. Large groups often come together to cooperatively hunt prey, which is quite varied and includes anchovy, squid and shrimp. The species may also feed at night. The dusky dolphin frequently associates with other cetaceans, and is said to be one of the most acrobatic of all dolphins, readily approaching boats to bow-ride, and often leaping high out of the water and tumbling in the air. Mating is believed to occur in spring, with a single calf born after a gestation period of 11 months and measuring around 55 to 70 centimetres at birth. Births usually peak in summer (November to February) around New Zealand and Argentina, and in winter (August to October) around Peru. Calves are weaned at around 18 months.


Dusky dolphins are widespread in the southern Hemisphere (Brownell and Cipriano 1999). They occur in apparently disjunct subpopulations in the waters off Tasmania, southern Australia, New Zealand (including the Chatham and Campbell Islands), central and southern South America (including the Falkland Islands), and southwestern Africa. They also occur around some oceanic island groups (e.g., Tristan da Cunha, Prince Edward, Amsterdam, and St. Paul Islands).


Habitat and Ecology

This coastal species is usually found over the continental shelf and slope (Jefferson et al. 1993; Aguayo et al. 1998). The distribution of dusky dolphins along the west coast of South Africa and both coasts of South America is associated with the continental shelves and cool waters of the Benguela, Humboldt and Falkland Currents. Around New Zealand, these dolphins are associated mainly with various cold water currents (Brownell and Cipriano 1999). Van Waerebeek et al. (1995) suggested that dusky dolphins may be limited to water shallower than 200 m. Off Argentina, dusky dolphins have been sighted from the coast to almost 200 nautical miles offshore, but the present information does not allow us to conclude whether this species' distribution tends to be more coastal than offshore or vice versa due to the bias in coastal effort (Crespo et al. 1997). They seem to prefer waters with sea surface temperatures between 10°C and 18°C (Brownell and Cipriano 1999). Inshore/offshore shifts in abundance have been noted for Argentina and New Zealand. They do move over deep waters in some areas (e.g., New Zealand), but always along continental slopes.

Dusky dolphins take a wide variety of prey, including southern anchovy near the surface in shallower waters, as well as midwater and benthic prey, such as squid, hake, and lanternfishes. They may also engage in nocturnal feeding, in association with the deep scattering layer. New Zealand dolphins appear to engage in feeding deeper in the water column than do those from Argentine waters (Cipriano 1992; Würsig et al. 1997).


Direct catches and bycatches have been large and continue in some regions. However, assessment of global population status is not possible with the currently available estimates of abundance and removals. The subpopulation off Peru has probably been overexploited but present data do not allow estimation of present decline.



Major Threats

Dusky dolphins are known to be taken directly in the multi-species small cetacean fisheries of Peru and Chile. An expanded directed fishery for dolphins and porpoises may have started in Peru after the demise of the anchoveta fishery in 1972. Although most dusky dolphins are taken in the directed net fishery they are also taken by a harpoon fishery (Brownell and Cipriano, 1999). It has been calculated that the fishing industry from just one port kills more than 700 dusky dolphins each year. 

Large catches (approximately 10,000) of small cetaceans were reported from the coastal waters of central Peru in 1985 (Read et al., 1988). In the 1991-1993 period, an estimated 7,000 dusky dolphins were captured per year, a level thought to be unsustainable. Of 722 cetaceans captured mostly in multi-filament gillnets and landed at Cerro Azul, central Peru, in 87 days during January- August 1994, 82.7% were dusky dolphins. The total kill estimate for a seven- month period, stratified by month, was 1,567 cetaceans. Data collected at 16 other ports showed that high levels of dolphin and porpoise mortality persisted in coastal Peru at least until August 1994. It is believed, but not confirmed, that this level of exploitation has diminished since dolphin hunting was banned by law in 1996, due in part to depletion of the regional population (Van Waerebeek and Würsig 2002). The current level of takes is unknown. The absence of abundance data precludes any assessment of impact on subpopulations (Van Waerebeek et al. 1997).

In New Zealand, some dusky dolphins are entangled in gill nets. Incidental mortality at one fishing port was estimated to be 100 to 200 animals per year (Jefferson et al. 1993). The highest rates of incidental catches off the Patagonian coast mostly occur in mid-water trawling for shrimp. At present, this fishery is declining in use, but in 1984, it reached a peak and the number of dolphins caught was estimated at between 442-560, decreasing during the following years. Mortality estimates for 1994 reached a minimum value of 36 dolphins per year, mostly females and young adults. Thus, incidental mortality during 1984-86, would have led to a maximum annual mortality close to 8% of the present estimated regional population size. The effect would have been severe, considering that the catches affected mostly females of the highest reproductive value (Dans et al. 1997).

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). Several hundred continue to die each year in various types of fishing gear off Argentina (Crespo et al. 2000). 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 (Würsiget al. 1997).
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