Doubtful Sound - Flora and Fauna

Flora and Fauna

Doubtful Sound (like many of the fiords in the area) is unusual in that it contains two distinct layers of water that scarcely mix. Dependant on rainfall the night before The top 2–10 meters is fresh water, fed from the high inflows from the surrounding mountains, and stained brown with tannins from the forest. Below this and partially insulated by the fresh above is a layer of warmer, heavy, saline water from the sea. The dark tannins in the fresh water layer makes it difficult for light to penetrate. Thus, many deep-sea species will grow in the comparatively shallow depths of the Sound. Such species include black coral (Antipatharia fiordensis) which is normally found at depths of 30–40 metres, but can be found at just 10 metres 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 Crown Fern, Blechnum discolor.

The fiord is home to one of the southernmost population of bottlenose dolphins. The Doubtful Sound bottlenoses have formed a very insular sub-group 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 for other bottlenose groups and is also overlaid by the freshwater layer. Recently (2000s), there is 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 or 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 rare large whales (Southern Right Whale, Humpback Whale, Minke Whale, Sperm Whale and some Giant Beaked Whales). Orca, the 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.