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{{Taxobox
| name = Dusky dolphin
| status = DD
| status_ref =<ref name=iucn>{{IUCN2008|assessors=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.|year=2008|id=11146|title=Lagenorhynchus obscurus|downloaded=06 March 2009}} Database entry includes a lengthy justification of why this species is listed as data deficient.</ref>
| status_system = iucn3.1
| image =DuskyDolphin.jpg
| image_width = 250px
| image2 = Dusky dolphin size.svg
| image2_width = 250px
| image2_caption = Size comparison against an average human
| regnum = [[Animal]]ia
| phylum = [[Chordata]]
| classis = [[Mammal]]ia
| subclassis = [[Eutheria]]
| ordo = [[Cetacea]]
| subordo = [[Odontoceti]]
| familia = [[Delphinidae]]
| genus = ''[[Lagenorhynchus]]''
| species = '''''L. obscurus'''''
| binomial = ''Lagenorhynchus obscurus''
| binomial_authority = [[John Edward Gray|Gray]], 1828
| range_map = cetacea_range_map_Dusky_Dolphin.PNG
| range_map_width = 250px
| range_map_caption = Dusky Dolphin range
}}
The '''dusky dolphin''' (''Lagenorhynchus obscurus'') is a [[dolphin]] found in coastal waters in the [[Southern Hemisphere]]. Its [[specific epithet]] is [[Latin]] for "dark" or "dim". It is very closely [[genetics|genetically]] related to the [[Pacific white-sided dolphin]], but current scientific consensus is that they are distinct species. The dolphin's range is patchy with major populations around [[South America]], southwestern [[Africa]], [[New Zealand]] and various oceanic islands with some sightings around [[southern Australia]] and [[Tasmania]].
The dusky dolphin pefers cool currents and inshore waters but can be found offshore. It feeds on a variety of [[fish]] and [[squid]] species and has flexible hunting tactics. The dusky dolphin is known for its remarkable acrobatics, having a number of [[Whale_surfacing_behaviour#Breaching.2C_lunging.2C_and_porpoising|aerial behaviors]]. The status of the dolphin is unknown but it has been commonly caught in [[gillnet|gill nets]].
==Taxonomy==
It is commonly thought that the dusky dolphin was first described by [[John Edward Gray]] in 1828 from stuffed skin and a single skull shipped from the [[Cape of Good Hope]] to the [[British Museum]]. Gray first described the species as ''Delphinus obscurus'', with the [[subgenus]] ''Grampus'' in his 1828 ''Specilegia Zoologica''. Gray reported that the animal was captured around the Cape of Good Hope by a Captain Haviside (often misspelt "Heaviside") and sent to the British Museum though the [[Royal College of Surgeons]] in 1827.<ref name=HMM>{{cite book|author=Ridgway, Sam H. |year=|title=Handbook of Marine Mammals: The second book of dolphins and the porpoises, Volume 6 |year=1998 |publisher=Elsevier|pages=85-95|url=http://books.google.com.au/books?id=At4jWmmaq6QC&pg=PA85&dq=Dusky+dolphin&hl=en&ei=792STcTjMcPIcYCjrYkH&sa=X&oi=book_result&ct=result&resnum=8&ved=0CFYQ6AEwBw#v=onepage&q=Dusky%20dolphin&f=false|isbn=0125885067}} </ref>
[[File:Pacific white side dolphin.jpg|thumb|250px|left|The dusky dolphin resembles, and is closely related to, the [[Pacific white-sided dolphin]].]]
However Gray later wrote that a similar dolphin was described as ''Delphinus supercilious'' by French surgeons and naturalists [[René Primevère Lesson]] and Prosper Garnot from a specimen collected off the coast of [[Tasmania]] two years before his own classification.<ref>{{cite journal |last=Gray |first=J. E. |year=1846 |title=On the British Cetacea |journal=The Annuals and Magazine of Natural History |location=London |volume=17 |pages=82–5}}</ref> Gray considered ''D. supercilious'' to be a junior [[Synonym (taxonomy)|synonym]] of his ''D. obscurus'' and gives Lesson and Garnot (1826) credit for their original description. Meanwhile, [[Charles Darwin]] also described what turned out to be this species as ''Delphinus fitzroyi'' from a specimen harpooned off Argentina in 1838. The dusky dolphin was reclassified as ''Prodelphinus obscurus'' in 1885 by British naturalist [[William Henry Flower]],<ref>{{cite book|author=Flower, W. H.|year=1885|title=List of the specimens of Cetacea in the Zoological Department of the British Museum|publisher=British Museum|location= London|pages=28-29|url=http://www.archive.org/stream/listofspecimenso00brituoft#page/28/mode/2up/search/obscurus}} </ref> before gaining its current binomial name, ''Lagenorhynchus obscurus'', from American biologist [[Frederick W. True]] in 1889.<ref>{{cite journal|author=True, F.W.|year=1889|title=Contribution to the natural history of the cetaceans: a review of the family Delphinidae|journal= Bulletin of the U.S. National Museum|volume=36|pages=1-191}}</ref>
===Genetics===
The dusky dolphin and the [[Pacific white-sided dolphin]] are considered [[phylogenetically]] related species. Some researchers have suggested that they are the same species but close scrutiny of morphological and life history parameters does not support this.<ref name= "Perrin"/> The two sister species diverged at around 1.9–3.0 million years ago.<ref name="Pmid">{{cite journal |last1=Cassens |first1=I |last2=Van Waerebeek |first2=K |last3=Best |first3=PB |last4=Tzika |first4=A |last5=Van Helden |first5=AL |last6=Crespo |first6=EA |last7=Milinkovitch |first7=MC |title=Evidence for male dispersal along the coasts but no migration in pelagic waters in dusky dolphins (''Lagenorhynchus obscurus''). |journal=Molecular ecology |volume=14 |issue=1 |pages=107–21 |year=2005 |pmid=15643955 |doi=10.1111/j.1365-294X.2004.02407.x}}</ref> Recent analysis of the mitochondrial cytochrome b gene indicates that the genus Lagenorhynchus, as traditionally conceived, is not a natural (monophyletic) group.<ref>LeDuc, R.G., Perrin, W.F., Dizon, A.E. (1999) "Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences", ''Marine Mammal Science'' 15(3):619–48.</ref> Another study finds that the dusky and the Pacific white-sided dolphin form the [[Sister_taxon#Cladograms|sister group]] to the (expanded) genus ''[[Cephalorhynchus]]''. If this placement is accurate, a new genus name will need to be coined to accommodate these two species.<ref>May-Collado, L., Agnarsson, I. (2006) "Cytochrome b and Bayesian inference of whale phylogeny", ''Molecular Phylogenetics and Evolution'' 38(2):344-54.</ref>
Dusky dolphins from Argentina and southwest Africa separated 2000 generations ago from an ancestral Atlantic population and since then diverged without much [[gene flow]].<ref name="Pmid" /> Most populations have low genetic diversity, with the Peruvian population being an expectation.<ref name= "Perrin"/> Possible hybrids of dusky dolphins have been described with a [[long-beaked common dolphin]]<ref>{{cite journal |last1=Reyes |first1=Julio C. |title=A Possible Case of Hybridism in Wild Dolphins |journal=Marine Mammal Science |volume=12 |pages=301–07 |year=1996 |doi=10.1111/j.1748-7692.1996.tb00581.x}}</ref> and a [[southern right whale dolphin]].<ref>{{cite journal |first1=Parissa |last1=Yazdi |year=2002 |url=http://www.aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/2002/AquaticMammals_28-02/28-02_Yazdi.pdf |title=A possible hybrid between the dusky dolphin (''Lagenorhynchus obscurus'') and the southern right whale dolphin (''Lissodelphis peronii'') |journal=Aquatic Mammals |volume=28 |pages=211–17}}</ref>
==Description==
[[File:Dusky dolphin NZ.jpg|thumb|250px|right|Closeup of front half of dusky dolphin]]
[[File:Dusky dolphin NZ 2.jpg|thumb|250px|left|Closeup of back half of dusky dolphin]]
The dusky dolphin is small to medium in length compared with other species in the family. There is significant variation in size among the different population areas. The largest dusky dolphins have been encountered off the coast of Peru, where they are up to 210 cm (6 feet) in length and 100 kg (210 pounds) in mass. The size for dusky dolphins in New Zealand have been recorded to be a length range of 167–178 cm and a weight range of 69–78 kg for females and a length range of 165–175 cm and a weigh range of 70–85 kg for males.<ref name= "Cipriano 1992">{{cite book |last=Cipriano |first=F. W. |year=1992 |title=Behavior and occurrence patterns, feeding ecology, and life history of dusky dolphins (''Lagenorhynchus obscurus'') off Kaikoura, New Zealand |type=Phd. Thesis |publisher=University of Arizona}}</ref> There is almost no [[sexual dimorphism]] in this species, although males have more curved dorsal fins with broader bases and greater surface areas.<ref name= "Perrin"/> The back of the dolphin is dark grey or black, and the [[dorsal fin]] is distinctively two-toned—the leading edge matches the back in color, but the trailing edge is a much lighter greyish white. Dusky dolphins have a long, light grey patch on their foreside leading to a short, dark grey beak. The throat and belly are white,<ref>Webber, M.C. 1987. "A comparison of dusky and Pacific white-sided dolphins (genus . Lagenorhynchus): morphology and distribution". M.S. Thesis, San Francisco State Univeristy, San Franciso CA. 102 pp.</ref> and the beak and lower jaw are dark grey. There are two blazes of white color running back on the body from the dorsal fin to the tail. Right between the white areas remains a characteristic thorn-shaped patch of dark colour, by which the species can easily be recognized. Aside from that, dusky dolphins may be confused with other members of their genus when observed at sea.
It can be distinguished from the [[common dolphin]]s, which have a more prominent and longer beak and yellow flank markings.<ref name=Menkhorst>{{cite book|last=Menkhorst|first=Peter|title=A Field Guide to Mammals of Australia|publisher=Oxford University Press|location=South Melbourne, Victoria|date=2001|pages=226-27|isbn=0-19-550870-X}}</ref> The skull of a dusky dolphin has a longer and narrower rostrum than that of a [[hourglass dolphin]] or [[Peale's dolphin]] of similar age and size.<ref>Fraser, F. C. 1966: Comments on the Delphinoidea. In: "Whales, Dolphins and. Porpoises," K. S, Norris (Ed.), pp. 7-37, University of California Press. ISBN 0520032837
</ref>
==Populations and distribution==
[[File:Dusky dolphin Kaikoura.jpg|thumb|250px|left|Dusky dolphins off New Zealand]]
The dusky dolphin has a discontinuous semi-[[wikt:circumpolar|circumpolar]] range. The dolphins can be found off the coasts of South America, southwestern Africa, southern Australia and Tasmania, New Zealand and some oceanic islands. Off South America, dusky dolphins range from southern Peru to [[Cape Horn]] in the west and from southern [[Patagonia]] to around 36º S in the east.<ref name= "Perrin">Waerebeek, K. V., Wursi, B. "Dusky Dolphin ''Lagenorhynchus obscurus''" pp. 335–37 of ''Encyclopedia of Marine Mammals'' (edited by Perrin, W. F., Wursig, B and J. G.M. Thewissen), Academic Press; 2nd edition, (2008) ISBN 012373553X
</ref> Its range also includes the [[Falkland Islands]]. They are particularly common from [[Peninsula Valdes]] to [[Mar de Plata]]. They are relatively uncommon in the [[Beagle Channel]] and the inshore waters of the [[Tierra del Fuego]] region.<ref>{{cite journal |author=Goodall, R.; de Haro, J.; Fraga, F.; Iniquez, M.; Norris, K. |year=1997 |title=Sightings and behaviour of Peale's dolphins, ''Lagenorhynchus australis'', with notes on dusky dolphins, ''L. obscurus'', off southernmost South America |journal=International Whaling Commission Report |volume=47 |pages=757–75 |url=http://orton.catie.ac.cr/cgi-bin/wxis.exe/?IsisScript=LIBRI.xis&method=post&formato=2&cantidad=1&expresion=mfn=016672}}</ref>
Dusky dolphins are found throughout New Zealand waters. The center of their abundance is from [[East Cape]] and [[Cape Palliser]] on the [[North Island]] to [[Timaru]] and Oamaru on the [[South Island]].<ref name= "Gaskin 1972">Gaskin, D E. (1972) [http://www.andrewisles.com/all-stock/publication/whales-dolphins-and-seals-with-special-reference-to-the-new-zealand-region "Whales dolphins and seals with special reference to the New Zealand region"]. Heinemann Educational Books Ltd.</ref> They are especially common in the cold waters of the Southland and Canterbury currents.<ref name= "Gaskin 1972"/> In Africa, the dusky dolphin ranges from Lobito Bay, Angola in the north to [[False Bay]], South Africa in the south.<ref name= "Perrin"/> Within Australian waters, Dusky dolphins have been recorded in colder waters off [[Kangaroo Island]], eastern Tasmania and [[Bass Strait]],<ref name=Menkhorst/> although they are uncommon and those that are sighted there are possibly transients from New Zealand.<ref>{{cite journal |last1=Gill |first1=Peter C. |last2=Ross |first2=Graham J. B. |last3=Dawbin |first3=William H. |last4=Wapstra |first4=Hans |title=CONFIRMED SIGHTINGS OF DUSKY DOLPHINS (''LAGENORHYNCHUS OBSCURUS'') IN SOUTHERN AUSTRALIAN WATERS |journal=Marine Mammal Science |volume=16 |pages=452–59 |year=2000 |doi=10.1111/j.1748-7692.2000.tb00937.x}}</ref> Dusky dolphins are also found around Campbell, Auckland and Chatham in the western South Pacific, [[Tristan da Cunha]] in the South Atlantic and [[Île Amsterdam]] and [[Île Saint-Paul]] in the southern Indian Ocean.<ref name= "Audubon">{{RefAudubonMarineMammals}}</ref>
==Ecology and behavior==
[[File:Dusky dolphin pod.jpg|thumb|250px|right|A pod of dusky dolphins]]
Dusky dolphins prefer cool, upwelling waters as well as cold currents. They largely live in inshore waters but can be found in the outer continental shelf and offshore islands.<ref name= "Gaskin 1972"/> Dusky dolphins can move over great distances (around 780 km) but have no well defined seasonal migrations.<ref name= "Perrin"/> However, dolphins off Argentina and New Zealand make inshore and offshore seasonal and diurnal movements.<ref name= "Perrin"/> In Argentina, dusky dolphins associate closely with [[southern right whale]]s and [[South American sea lion]]s.<ref name= "behavior"/> They have been found close to, but have apparently not interacted with, [[bottlenose dolphin]]s and may feed in the same areas as [[Risso's dolphin]]s.<ref name= "behavior"/> They also associate with various seabirds like [[kelp gull]]s, [[cormorant]]s, [[tern]]s, [[shearwater]]s, [[petrel]]s and [[albatross]]es.<ref name= "behavior"/> In New Zealand, dusky dolphins mingle with [[common dolphins]].<ref name= "Cipriano 1992"/> Dusky dolphins have also been observed with [[southern right whale dolphin]]s and [[pilot whale]]s off southwestern Africa.<ref>Cruickshank, R.A. & S.G. Brown (1981) "Recent observations and some historical records of southern right-whale dolphins ''Lissodelphis peronii''", ''South African Fishery Bulletin'', 15(1):109–21. [http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=196180&q=Recent+observations+and+some+historical+records+of+southern+right-whale+dolphins&uid=789414412&setcookie=yes Abstract]</ref>
===Vocalizations and echolocation===
In general three different types of sounds are produced by dolphins (and other [[toothed whales]]). These are click trains, which are a series of individual clicks, usually broadband signals with a rapid rise time,<ref>Caldwell, M.C; Caldwell D.K (1971) "Underwater pulsed sounds produced by captive spotted dolphins, Stenella plagiodon", ''Cetology'' 1:1–7.</ref> burst pulses, which are individual clicks whose repetition is so high that they are heard by humans only as a buzzing sound<ref name = "Yin 1999"/> and whistles, which are pure-tone, narrow-banded frequency modulated signals which vary in frequency with time. Dusky dolphins have been recorded to make all three sounds but most commonly make burst pulses.<ref name = "Yin 1999">SE Yin (1999) [http://reference.kfupm.edu.sa/content/m/o/movement_patterns__behaviors__and_whistl_76082.pdf "Movement patterns, behaviors, and whistle sounds of dolphin groups off Kaikoura, New Zealand"], A Thesis, Texas A&M University, College Station, TX.</ref> Whistling is more common when dusky dolphins mingled with other dolphin species like [[common dolphin]]s.<ref name= "acoustics">Au, W.W.L.; Lammer, M.O; Yin, S."Acoustics of Dusky Dolphin (''Lagenorhynchus obscurus'')". Pp. 75–98 in: Würsig, B., and Würsig, M., editors. ''The Dusky Dolphin: Master Acrobat off Different Shores''. Academic Press. (2010) ISBN 0123737230</ref>{{rp|79}} Dusky dolphins project broadband short-duration [[Animal echolocation|echolocation]] signals similar to that of other whistle-producing toothed whales.<ref name= "acoustics"/>{{rp|95}} Most of the species' echolocation signals have bi-modal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 80 and 110 kHz.<ref name= "echolocation">{{cite journal |last1=Au |first1=WW |last2=Würsig |first2=B |title=Echolocation signals of dusky dolphins (''Lagenorhynchus obscurus'') in Kaikoura, New Zealand. |journal=The Journal of the Acoustical Society of America |volume=115 |issue=5 Pt 1 |pages=2307–13 |year=2004 |pmid=15139642}}</ref> The levels of the echolocation signals are about 9–12 [[Decibel|dB]] lower than for the larger [[white-beaked dolphin]] which belongs to the same genus but is over twice as heavy as the dusky dolphins.<ref name= "echolocation"/>
===Foraging and predation===
[[File:Dusky dolphins.jpg|thumb|250px|left|A dusky dolphin pair]]
Dusky dolphins prey consume a variety of fish and squid species. Common fish species eaten include [[anchovies]], [[lantern fish]], [[pilchard]]s, [[sculpin]]s, [[hake]]s, [[horse mackerel]], [[Blue grenadier|hoki]] and [[Red codling|red cod]].<ref name= "Perrin"/> They are generally coordinate hunters. These dolphins have very flexible foraging strategies that can change depending on the environment.<ref name= "Benoit 2004">Benoit-Bird, K.J., Würsig, B., and McFadden, C.J. 2004. "[http://people.oregonstate.edu/~benoitbk/reprints/dusky%20foraging%20mms.pdf Dusky dolphin (''Lagenorhynchus obscurus'') foraging in two different habitats: active acoustic detection of dolphins and their prey]." ''Marine Mammal Science'' '''20'''(2): 215–31.</ref> In certain parts of New Zealand, were deep oceanic waters meet the shore, dusky dolphins forage in [[deep scattering layer]]s at night.<ref name= "Benoit 2004"/> They arrive at the hunting site individually but form groups when in the layer.<ref name= "Benoit 2004"/> The dolphins use their echolocation to detect and isolate an individual prey.<ref name="echolocation" /> Groups of foraging dolphins tend to increase when the layer is near the surface and decrease when it descends.<ref name= "Benoit 2004"/>
When hunting in shallower waters in New Zealand and Argentina, dusky dolphins tend to forage during the day. The dolphins chase schools of fish or squid and herd them into stationary balls.<ref name= "McFadden 2003">McFadden, C. J. (2003). "Behavioral flexibility of feeding dusky dolphins (Lagenorhynchus obscurus) in Admiralty Bay, New Zealand." M.Sc. thesis, Texas A&M University, College Station , TX.</ref> They may control the school by using light reflected from their white bellies.<ref>{{cite book |last1=Würsig |first1=B. |first2=T. R. |last2=Kieckhefer |first3=T. A. |last3=Jefferson |year=1990 |chapter=Visual displays for communication in cetaceans |pages=545–59 |title=Sensory Abilities of Cetaceans |editor1-first=J. |editor1-last=Thomas |editor2-first=R. |editor2-last=Kastelein |publisher=Plenum Press |isbn=0306436957}}</ref> Dolphins herd prey against the surface but also horizontally against the shore, a point of land or the hull of a boat.<ref name= "McFadden 2003"/> During these times, it is believed that dusky dolphins increase prey availability for other predators including other dolphins, [[seabird]]s, [[shark]]s and [[pinniped]]s. In Argentina, dusky dolphins may use bird aggregations to coordinate foraging efforts.<ref name= "behavior"/> On the other hand, pinnipeds and sharks [[Kleptoparasitism|take advantage]] of the dolphin hunts which leave almost no advantage to the dolphins.<ref name = "Markowitz 2004">Markowitz, T.M. (2004). "Social organization of the New Zealand dusky dolphin". Ph.D . dissertation, Texas A&M University, College Station.</ref> Dusky dolphins are themselves preyed on by [[killer whale]]s and large sharks. Dolphins avoid killer whales by swimming into shallower water.<ref name= "behavior">Würsig, B.; Würsig, M. (1980) [http://fishbull.noaa.gov/77-4/wursig.pdf "Behavior and ecology of the dusky dolphin, Lagenorhynchus obscurus, in the South Atlantic"]. ''Fishery Bulletin'' 77: 871–90.</ref> Dusky dolphins are also susceptible to [[parasitism]] by certain [[nematode]], [[cestode]] and [[trematode]] species, mostly ''Nasitrema'' sp., ''[[Anisakis]]'' sp., ''Phyllobothrium delphini'', ''Braunina cordiformis'' and ''Pholeter gasterophilus''.<ref>Van Waerebeek K, Reyes JC, Alfaro J (1993) [http://www.aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/1993/Aquatic_Mammals_19_3/19-03_VanWaerebeek.pdf "Helminth parasites and phoronts of dusky dolphins Lagenorhynchus obscurus (Gray, 1828) from Peru".] ''Aquat Mamm'' '''19'''(3):159–69.</ref>
===Social behavior and reproduction===
[[Image:duskyd.jpg|thumb|right|250px|A pair of dusky dolphins breaching]]
Dusky dolphins live in a [[fission-fusion society]] with most group size increases occurring during foraging and decreases in group sizes occurring during resting and traveling. In the Golfo San José off the [[Valdes Peninsula]], dolphins encounter a variety of associates by switching between small traveling groups and large socio-sexual groups. Studies of dolphins off [[Kaikoura]], New Zealand show that dolphins normally live in large groups that split into smaller sub-groups.<ref name = "Markowitz 2004"/> These sub-groups are composed of mating adults (mating groups), mothers with calves (nursery groups) and non-breeding adults.<ref name = "Markowitz 2004"/> Dusky dolphins have a [[promiscuous]] mating system in which both males and females mate with multiple partners. Mating groups are generally made of around ten males and a single female.<ref name = "Markowitz 2004"/> These mating groups can be found in both shallow and deep water but more often gather near shore.<ref name = "mating">Markowitz, T.M.; Markowitz, W.J.; and Morton, L.M. "Mating habits of New Zealand dusky dolphins". Pp. 151–76 in: Würsig, B., and Würsig, M., editors. ''The Dusky Dolphin: Master Acrobat off Different Shores''. Academic Press. (2010) ISBN 0123737230.</ref>{{rp|162}}
In the mating groups, the males pursue the female in high speed chases. Male reproductive success seems to be determined by speed and agility rather than size, strength or aggression.<ref name = "mating"/>{{rp|164}}{{rp|175}} Females exercise their choice in sexual partners by extending the chase as long as possible.<ref>Whitehead, H.; and Mann, J. (2000). "Female reproductive strategies of cetaceans". In ''Cetacean Societies''. Mann, J., editior. University of Chicago Press, pp. 219–246. ISBN 0226503410</ref> Females may opt to evade males that fail to demonstrate vigor or social skill.<ref name = "mating"/>{{rp|170}} It is also possible that males may form alliances to catch females.<ref name = "mating"/>{{rp|167–69}} Unlike male [[bottlenose dolphin]]s, male dusky dolphins can't monopolize females.<ref name = "mating"/>{{rp|166}} The time when female dusky dolphins first reproduce varies between regions. New Zealand dolphins first reproduce at about 7–8 years with 6–7 years for Argentine dolphins. A study of dusky dolphins off the coast of Peru showed the reproductive cycle to be around 28.6 months, mother dolphins would be pregnant for 12.9 months, lactate for a further 12 months and rest for 3.7 months before beginning the cycle again.<ref name=HMM/> During copulation, females tend to be on the top.<ref name = "mating"/>{{rp|170}} As with all species where females mate with multiple partners, male dusky dolphins have large testicles for [[sperm competition]].<ref name = "mating"/>{{rp|166}} Dusky dolphins sometimes engage in sexual behavior for reasons other than reproduction, perhaps in greeting or communication. [[Homosexual behavior in animals|Homosexual behavior]] between males has been observed.<ref name = "Markowitz 2004"/> Social sexual behavior tends to be more relaxed.<ref name = "mating"/>{{rp|175}}
Females with calves tend to gather in nursery groups in shallow water. Nursery groups likely provide calves protection from predators and marauding males as well as benefits such as resting, foraging, socializing and social learning. <ref name = "calf">Weir, J.; Deutsch, S.; and Pearson, H.C. "Dusky Dolphin Calf Rearing". Pp. 177–94 in: Würsig, B.; and Würsig, M., editors. ''The Dusky Dolphin: Master Acrobat off Different Shores''. Academic Press. (2010) ISBN 0123737230.</ref> The formation of nursery groups may grant mothers and calves increased time for rest which is important for growing calves and females which face increased energetic constraints due to lactation. While the behaviors of nursery groups vary by month, resting is the predominant behavior during most months. <ref name = "calf"/>{{rp|188}} The formation of nursery groups in shallow waters also allow members to exploit prey species other than those found in deep scattering layers. Both adults and calves have been observed to chase and catch fish and the adults may be teaching the calves how to hunt. <ref name = "calf"/>{{rp|188-89}} In contrast to shallower waters, hunting in deep water at night may be too dangerous for calves. <ref name = "calf"/>{{rp|189}} Calves are particularly vulnerable to predators like killer whales and use of shallow water by nursery groups may be a predator avoidance strategy. <ref name = "calf"/>{{rp|183}} Nursery groups tend to avoid mating groups. <ref name = "mating"/>{{rp|174}} Adult males in these groups will aggressively herd and chase single females. This may create a dangerous situation for calves has they may become separated from their mothers and may themselves become subjects of adult male harassment. <ref name = "calf"/>{{rp|185}} Calves may also become exhausted, disorientated and more vulnerable to predation. <ref name = "calf"/>{{rp|185}} Mother dolphins may [[Alloparenting|look after calves that are not their own]].<ref name = "calf"/>{{rp|192}}
[[Image:DuskyJump.jpg|thumb|left|250px|Dusky dolphins leaping]]
===Aerial behavior===
Dusky dolphins perform a number of aerial displays. Displays include leaps, backslaps, headslaps, tailslaps, spins and noseouts.<ref name= "behavior"/> The dolphins also perform head-over-tail leaps which is considered the most "acrobatic" of the displays.<ref name= "behavior"/> A headfirst re-entry is performed when a dolphin leaps clear out of the water and then arches its back strongly while flipping the tail to make a headfirst re-entry. In "humping", the same motion occurs expect the snout and tail do not leave the water during the arch.<ref name= "behavior"/> Leaps, head-over-tail leaps, backslaps, headslaps, tailslaps and spins often occur in groups. One dolphin starts a particular leap and then continues it 3–20 times.<ref name= "behavior"/> Young dusky dolphins apparently are not born with the ability to perform the leaps and must learn to master each one.<ref name = "calf"/>{{rp|190}} Calves appear to first learn how to perform noisy leaps, followed by head first re-entries, coordinated leaps and finall acrobatic leaps.<ref name = "calf"/>{{rp|190–91}} Adult dusky dolphins may perform different leaps in different contexts and calves may independently learn how to perform leaps but learn when to perform with interactions with others.<ref name = "calf"/>{{rp|191}}
==Relationship with humans==
[[File:6208-MarineLandDolphinShow.jpg|thumb|250px|right|Pacific white-sided dolphins at a [[dolphinarium]]. Dusky dolphins normally do not do well in captivity.<ref name= "Perrin"/>]]
===Status===
The dusky dolphin is protected in much of its range. Although dusky dolphins are considered abundant, few population estimates are available.<ref name= "Audubon"/> 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.<ref name=iucn/> 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.<ref name=iucn/> Unknown numbers were caught in gill nets in New Zealand, although currents catches have dropped in numbers from ones in the 1970s and 1980s.<ref name= "Perrin"/> The dolphins are also thought to have been harpooned off South Africa, but the numbers are not considered large.<ref name= "Audubon"/>
===Mussel farming===
The effect of [[Mussel#Aquaculture|mussel farming]] on dusky dolphins has been studied in [[Admiralty Bay, New Zealand]]. Regular seasonal migration of dusky dolphins and frequent feeding associations with other apex predators make management of marine farming a wider socio-economic and ecological issue.<ref name= "mussel farm">{{cite journal |last1=Markowitz |first1=Tim M. |last2=Harlin |first2=April D. |last3=Würsig |first3=Bernd |last4=McFadden |first4=Cynthia J. |title=Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand |journal=Aquatic Conservation: Marine and Freshwater Ecosystems |volume=14 |pages=133–49 |year=2004 |doi=10.1002/aqc.602}}</ref> Dusky dolphins are most often encountered during the winter in Admiralty Bay, the area with the greatest density of proposed farming activity in the region. The dolphins rarely used areas in existing farms and few are observed to enter the boundaries of them.<ref name= "mussel farm"/> Dolphins that enter mussel farms move rapidly up the lanes between rows of lines and floats.<ref name= "mussel farm"/>
===Tourism===
[[File:South Island Tour 239.jpg|thumb|250px|right|Dusky dolphin tours off New Zealand's [[South Island]]]]
Dusky dolphins are popular attractions for whale-watching tours. Since 1997, dolphin watching activities have increased in Patagonia, with dusky dolphins (along with [[Commerson's dolphin]]s) as the target species.<ref name= "Coscarella 2003">Coscarella, M. A, Dans, S. L, Crespo, E. A, Pedraza, S. N. (2003) "Potential impact of unregulated dolphin watching activities in Patagonia". ''J Cetacean Res Manag'' 5: 77–84. [http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=5789969&q=Potential+impact+of+unregulated+dolphin+watching+activities+in+Patagonia&uid=790376810&setcookie=yes Abstract]</ref> For dusky dolphins, the number of tourists increased from 1,393 in 1997 to 1,840 in 2000. The encounter rate grew from 25% during 1999 to 90% in 2001. Most of the groups observed ranged from 50–100 animals.<ref name= "Coscarella 2003"/> Dolphin watching in this areas started as an alternative to whale watching, mostly based on that of the [[southern right whale]].<ref name= "Coscarella 2003"/> Dusky dolphin watching is also popular in New Zealand, whose dolphin watching industry begin in the late 1980s. Whale and dolphin watching tours have grown in since then, with the number of permitted dolphin tour operators increasing from none to over 75 since the late 1980s.<ref name = "tourism"/>{{rp|235}} New Zealand has several locations to view and swim with dusky dolphins, notably in [[Marlborough Sounds]].<ref name = "tourism">Markowitz, T.M.; Dans, S.L.; Crespo, E.A.; Lundquist, D.L.; and Duprey, N.M.T. "Human interactions with dusky dolphins: harvest, fisheries, habitat alteration, and tourism". Pp. 211–44 in: Würsig, B., and Würsig, M., editors. ''The Dusky Dolphin: Master Acrobat off Different Shores''. Academic Press. (2010) ISBN 0123737230.</ref>{{rp|236}}
While dusky dolphin tourism is a larger industry in New Zealand than it is in Argentina, the effects of tourism on the dolphins seem to be lower in the former than the latter.<ref name = "tourism"/>{{rp|241}} New Zealand tours are operated under permits, whose numbers are limited and are accompanied by conditions and guidelines related to approach procedures and swim operations.<ref name = "tourism"/>{{rp|241}} By contrast, there is no direct regulation of dolphin watching in Argentina.<ref name= "Coscarella 2003"/> As such, dolphin activities are often disturbed by touring vessels.<ref name = "tourism"/>{{rp|233-35}}
==References==
{{reflist}}
===General===
*''Encyclopedia of Marine Mammals''. Perrin, W. F., Wursig, B and J. G.M. Thewissen., editors. (2008) Academic Press; 2nd edition, ISBN 012373553X
*''The Dusky Dolphin: Master Acrobat off Different Shores''. Würsig, B., and Würsig, M., editors. (2010) Academic Press. ISBN 0123737230.
*''Whales, Dolphins and. Porpoises'', K. S, Norris. editor, (1977) University of California Press. ISBN 0520032837
*''Sensory Abilities of Cetaceans''. Thomas, J.; Kastelein, R., editors. (1990) Plenum Press. ISBN 0306436957.
*''Cetacean Societies''. Mann, J., editor. (2000) University of Chicago Press, ISBN 0226503410.
== External links ==
{{Commons|Lagenorhynchus obscurus}}
*ARKive – [http://www.arkive.org/species/GES/mammals/Lagenorhynchus_obscurus/ images and movies of the dusky dolphin ''(Lagenorhynchus obscurus)'']
*[http://www.wdcs.org: Whale and Dolphin Conservation Society]
{{Cetacea|O.}}
{{Use dmy dates|date=March 2011}}
{{DEFAULTSORT:Dusky Dolphin}}
[[Category:Oceanic dolphins]]
[[Category:Mammals of South America]]
[[Category:Mammals of Argentina]]
[[Category:Mammals of Chile]]
[[Category:Mammals of Peru]]
[[Category:Mammals of Africa]]
[[Category:Mammals of New Zealand]]
[[Category:Cetaceans of Australia]]
[[Category:Fauna of the Pacific Ocean]]
[[ca:Dofí fosc]]
[[de:Schwarzdelfin]]
[[es:Lagenorhynchus obscurus]]
[[fr:Dauphin obscur]]
[[it:Lagenorhynchus obscurus]]
[[hu:Sötét delfin]]
[[nl:Donkergestreepte dolfijn]]
[[ja:ハラジロカマイルカ]]
[[pl:Delfin ciemny]]
[[pt:Golfinho-do-crepúsculo]]
[[ru:Тёмный дельфин]]
[[sr:Lagenorhynchus obscurus]]
[[sv:Södra Atlantvitsiding]]
[[tr:Gölgeli yunus]]
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