|Scientific Name:||Lagenorhynchus obscurus|
|Species Authority:||(Gray, 1828)|
|Taxonomic Notes:||The genus Lagenorhynchus is likely an artificial genus (LeDuc et al. 1999), and this species may eventually be included in the genus Sagmatias.
Three subspecies are recognized: L. o. obscurus in southern Africa, L. o. fitzroyi in southern South America, and an un-named subspecies in New Zealand (Perrin 2002). Recent genetic evidence suggests that, despite some gene flow, Peruvian and Argentine animals should be considered separate subpopulations (Brownell and Cipriano 1999). Subpopulations centered in New Zealand, the west coast of South America, and southwestern Africa are genetically distinct and all may deserve subspecies status (Würsig et al. 1997, Van Waerebeek 1993).
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B.|
|Reviewer/s:||Rojas-Bracho, L. & Smith, B.D. (Cetacean Red List Authority)|
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.
|Range Description:||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).|
Native:Argentina; Australia; Chile; Falkland Islands (Malvinas); French Southern Territories (the) (Amsterdam-St. Paul Is.); Namibia; New Zealand; Peru; South Africa (Marion-Prince Edward Is., Northern Cape Province)
|FAO Marine Fishing Areas:||
Atlantic – southeast; Atlantic – southwest; Pacific – southeast; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
There are few abundance estimates available for any significant portion of the range (Brownell and Cipriano, 1999). The total number of dusky dolphins in the one area off the Patagonian cost was estimated to be close to 7,252 individuals (Dans et al. 1997), and the number given by Schiavini et al. (1999) for the area between Punta Ninfas and Cabo Blanco, Argentina is 6,628. Some subpopulations are thought to have been seriously depleted by human activities (e.g., those off Peru, Van Waerebeek 1994.).
There is a hiatus in distribution spanning about 1,000 km along the Chilean coast, and the animals off Patagonia are smaller than those off northern Chile and Peru, suggesting that the subpopulations in western and eastern South America are separate. 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 (Brownell and Cipriano 1999).
|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).
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 (Würsig et al. 1997).
The species is listed in Appendix II of CITES.
Subpopulation definitions and numbers are unknown for New Zealand and other areas, and intensive photo-identification, genetic and survey studies are recommended.
Bycatch in gillnets occurs at an unknown level and needs to be investigated.
Aguayo, A., Bernal, R., Olavarria, C., Vallejos, V. and Hucke, R. 1998. Observaciones de cetaceos realizados entre valparaiso e isla de Pascua, Chile, durante los inviernos de 1993, 1994, 1995. Revista de Biologia Marina y Oceanografia 33: 101-123.
Brownell Jr., R. L. and Cipriano, F. 1999. Dusky dolphin Lagenorhynchus obscurus (Gray, 1828). In: S. H. Ridgway and R. Harrison (eds), Handbook of marine mammals, Vol. 6: The second book of dolphins and the porpoises, pp. 85-104. Academic Press, San Diego, USA.
Cipriano, F. W. 1992. Behavior and occurrence patterns, feeding ecology, and life history of dusky dolphins (Lagenorhynchus obscurus) off Kaikoura, New Zealand. Thesis, University of Arizona.
Crespo, E. A., Alonso, M. K., Dans, S. L., Garcia, N. A., Pedraza, S. N., Coscarella, M. and Gonzalez, R. 2000. Incidental catches of dolphins in mid-water trawls for Argentine anchovy (Engraulis anchoita) off the Argentine shelf. Journal of Cetacean Research and Management 2(1): 11-16.
Crespo, E. A., Pedraza, S. N., Coscarella, M., Garcia, N. A., Dans, S. L., Iniguez, M., Reyes, L. M., Alonso, M. K., Schiavini, A. C. M. and Gonzalez, R. 1997. Distribution and school size of dusky dolphins, Lagenorhynchus obscurus (Gray, 1828), in the southwestern South Atlantic Ocean. Reports of the International Whaling Commission 47: 693-698.
Dans, S. L., Crespo, E. A., Garcia, N. A., Reyes, L. M., Pedraza, S. N. and Alonso, M. K. 1997. Incidental mortality of Patagonian dusky dolphins in mid-water trawling: retrospective effects from the early 1980s. Reports of the International Whaling Commission 47: 699-703.
IUCN. 2008. 2008 IUCN Red List of Threatened Species. Available at: http://www.iucnredlist.org. (Accessed: 5 October 2008).
Jefferson, T. A., Leatherwood, S. and Webber, M. A. 1993. Marine Mammals of the World: FAO Species Identification Guide. United Nation Environment Programme and Food and Agricultural Organization of the UN.
Leduc, R. G., Perrin, W. F. and Dizon, A. E. 1999. Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences. Marine Mammal Science 15: 619-648.
Perrin, W. F. 2002. Geographic variation. In: W. F. Perrin, B. Wursig and J. G. M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 510-516. Academic Press.
Read, A. J., Van Waerebeek, K., Reyes, J. C., Mckinnon, J. S. and Lehman, L. C. 1988. The exploitation of small cetaceans in coastal Peru. Biological Conservation 46: 53-70.
Schiavini, A., Pedraza, S. N., Crespo, E. A., Gonzalez, R. and Dans, S. L. 1999. Abundance of dusky dolphins (Lagenorhynchus obscurus) off north and central Patagonia, Argentina, in spring and a comparison with incidental catch in fisheries. Marine Mammal Science 15: 828-840.
Van Waerebeek, K. 1993. External features of the dusky dolphin Lagenorhynchus obscurus (Gray, 1828) from Peruvian waters. Estudios Oceanologicos 12: 37-53.
Van Waerebeek, K. 1993. Geographic variation and sexual dimorphism in the skull of the dusky dolphin, Lagenorhynchus obscurus (Gray, 1828). Fishery Bulletin 91: 754-774.
Van Waerebeek, K. 1994. A note on the status of the dusky dolphins (Lagenorhynchus obscurus) off Peru. Reports of the International Whaling Commission 15: 525-527.
Van Waerebeek, K., Alfaro-Shigueto, J., Montes, D., Onton, K., Santillan, L., Van Bressem, M. F. and Vega, D. 2002. Fisheries related mortality of small cetaceans in neritic waters of Peru in 1999-2001. International Whaling Commission, Cambridge, UK.
Van Waerebeek, K. and Wursig, B. 2002. Pacific white-sided dolphin and dusky dolphin Lagenorhynchus obliquidens and L. obscurus. In: W. F. Perrin, B. Wursig and J. G. M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 859-861. Academic Press.
Van Waerebeek, K., van Bree, P. J. H. and Best, P. B. 1995. On the identity of Predelphinus petersii Lutken, 1889 and records of dusky dolphin Lagenorhynchus obscurus (Gray, 1828) from the southern Indian and Atlantic oceans. South African Journal of Marine Science 16: 25-35.
Van Waerebeek, K., Van Bressem, M. F., Felix, F., Alfaro-Shigueto, J., Garcia-Godos, A., Chavez-Lisambart, L., Onton, K., Montes, D. and Bello, R. 1997. Mortality of Dolphins and Porpoises in Coastal Fisheries off Peru and Southern Ecuador in 1994. Biological Conservation 81: 43-49.
Würsig, B., Cipriano, F., Slooten, E., Constantine, R., Barr, K. and Yin, S. 1997. Dusky Dolphins (Lagenorhynchus obscurus) off New Zealand: status of present knowledge. Report of the International Whaling Commission 47: 715-722.
|Citation:||Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. 2008. Lagenorhynchus obscurus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 24 May 2013.|
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