page_title: Doubtful Sound
section_title: Flora and fauna
hierarchical_section_title: Doubtful Sound / Flora and fauna
caption_attribution_description: English: Black coral (Antipathella fiordensis) and a sea star found at "the gut" dive site, Doubtful Sound, New Zealand
context_page_description: Doubtful Sound / Patea is a fjord in Fiordland, in the far south west of New Zealand. It is located in the same region as the smaller but more famous and accessible Milford Sound. It took second place after Milford Sound as New Zealand's most famous tourism destination.
  At 40 kilometres long, Doubtful Sound is the second longest, and with a depth of up to 421 metres the deepest of the South Island's fiords. In comparison with Milford Sound, it is more widespread, with the cliffs not as dramatically tall and near vertical. However, the U-shaped profile of the fiord is obvious, in particular on the two innermost of the main fiord's arms and the hanging side valleys along the main fiord.
  Like most of Fiordland, Doubtful Sound receives a high amount of rainfall, ranging from an annual average of 3,000–6,000 millimetres. The vegetation on the mountainous landscape surrounding the fiord is dense native rainforest.
context_section_description: Doubtful Sound (like many of the fiords in the area) is unusual in that it contains two distinct layers of water that scarcely mix. The surface layer 2–10 metres (5–35 ft), referred to as the Low Salinity Layer or LSL, consists of diluted seawater with a typical salinity value of less than 10 psu.  This layer receives fresh water fed from the high inflows from the surrounding mountains, and stained brown with tannins from the forest. The outflow of freshwater from the tailrace discharge from the Manapouri Power Station also influences the thickness of the LSL. Below the LSL is a layer of warmer, undiluted seawater with a salinity value of around 35 psu. The dark tannins in the fresh water layer make it difficult for light to penetrate. Thus, many deep-sea species grow in the comparatively shallow depths of the Sound. Such species include black coral Antipathes fiordensis, which is normally found at depths of 30–40 metres (100–130 ft) but can be found at just 10 metres (35 ft) in Doubtful Sound and is within the range of qualified recreational divers.
  The catchment basin of Doubtful Sound is generally steep terrain that is heavily forested except for locations where surface rock exposures are extensive. Nothofagus trees are dominant in many locations. In the understory there are a wide variety of shrubs and ferns, including the crown fern, Blechnum discolor.
  The fiord is home to one of the southernmost populations of bottlenose dolphins. The Doubtful Sound bottlenoses have formed a very insular subgroup of only about 70 individuals, with none having been observed to leave or enter the Sound during a multi-year monitoring regime. Their social grouping is thus extremely close, which is also partly attributed to the difficult and unusual features of their habitat, which is much colder than the habitats of other bottlenose groups and is also overlaid by the freshwater layer. Recently (2000s), there has been growing concern that the population is in significant decline, with calf survival rates having halved, as well as being noticeably lower than in captivity or in other New Zealand environments. The reasons for this are unclear, though increased tourism and the fresh-water discharge from the Manapouri Power Station (see Hydroelectricity section below) are considered potential causes.
  Other wildlife to be found in Doubtful Sound includes fur seals and penguins, or even large whales. Southern right whales and humpback whales are the most frequently seen especially the later. Others include minke whale, sperm whale and some giant beaked whales). Orcas (killer whales) and long-finned pilot whales can be found also. The waters of Doubtful Sound are also home to an abundance of sea creatures, including many species of fish, starfish, sea anemones, and corals. It is perhaps best known for its black coral trees which occur in unusually shallow water for what is normally a deep-water species. The sound has been identified as an Important Bird Area by BirdLife International because it is a breeding site for Fiordland penguins.
  Secretary Island and Bauza Island are some of the most important sanctuaries in New Zealand for critically endangered birds.
caption: An example of a black coral found at a depth of 15 metres (50 ft) in "the gut" area of the sound, complete with a snake star.
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