About 70 bottlenose dolphins, a breeding colony of Fiordland crested penguins and black coral growing just 10 metres below the surface are what set Doubtful Sound / Patea apart. It is a fiord in Fiordland National Park, in the far south-west of New Zealand’s South Island: 40 km long, the second-longest of the South Island’s fiords, and the deepest at up to 421 m. It lies inside the Te Wāhipounamu World Heritage Area (listed 1990), holds two marine reserves, and opens onto the Tasman Sea past Secretary Island, one of the largest pest-free islands in the country. No public road reaches it. Visitors cross Lake Manapouri by boat and then take a bus over Wilmot Pass to Deep Cove, the inner end of the sound. Its name goes back to James Cook, who in 1770 called it Doubtful Harbour because he was unsure a sailing ship could get back out. The sections below take its wildlife one place at a time, from the open water to Deep Cove.
A Pod of About 70 Bottlenose Dolphins That Never Leaves
Doubtful Sound holds one of the southernmost populations of bottlenose dolphins in the world, and one of the most closed. The resident group numbers only about 70 animals, and during a monitoring programme that ran for several years none was seen to leave or enter the sound. They form an unusually tight social group. Researchers link this partly to the habitat itself, which is much colder than the waters most bottlenose dolphins live in and is capped by a layer of fresh water.
That isolation also makes the pod vulnerable. In the 2000s scientists raised concern that it was in significant decline: calf survival had halved and was clearly lower than in captivity or in other New Zealand populations. The cause has not been settled. Two candidates are named most often: growing boat tourism on the sound, and the fresh-water discharge from the Manapōuri Power Station at Deep Cove. Milford Sound, 15 km long and reached by road, also has bottlenose dolphins, but no other group in the region has been recorded as quite so closed as the Doubtful Sound animals.
Tawaki: Fiordland Crested Penguins on Rolla Island
The Fiordland crested penguin, tawaki in Māori (Eudyptes pachyrhynchus), breeds in Doubtful Sound, and that colony is the reason BirdLife International lists the sound as an Important Bird Area. Within the sound, Rolla Island, on the southern side of the Taipari Roa marine reserve, is a known penguin habitat. The species is endemic to New Zealand and now breeds only along the south-west coasts of the South Island, on Stewart Island/Rakiura and on its outlying islands. Fossils have been found as far north as the northern end of the South Island, and it probably once nested in the North Island too. Its range was cut back by hunting in Polynesian times, which is why it survives mainly in the least-populated corner of the country.
Tawaki are medium-sized, about 55 cm long and 3.5 kg on average, with a broad yellow crest running from the bill over the eye. They nest among tree roots and rocks in dense coastal rainforest rather than on open beaches. Breeding birds come ashore in the height of winter and breed between July and December, staying on land for about 20 weeks until the chick leaves. Each clutch has two eggs, and the first, smaller egg usually hatches later and is less likely to survive. Studies of their diet found mostly cephalopods, about 85%, chiefly arrow squid, with krill and a little fish. Penguins living in the inner, middle and outer parts of a fiord forage differently: outer-fiord birds make longer, deeper dives, while mid-fiord birds feed mostly in the upper 20 m of water.
Black Coral at 10 Metres in the Taipari Roa (Elizabeth Island) Marine Reserve
Doubtful Sound has two layers of water that barely mix. The top 2–10 m, called the Low Salinity Layer, is diluted seawater with a salinity usually under 10 psu, fed by run-off from the mountains and stained brown by forest tannins. Below it lies warmer, full-strength seawater of around 35 psu. Because the dark surface layer blocks light, animals that usually live in deep water grow in the shallows. The best-known is the black coral Antipathella fiordensis, first described from Fiordland’s fiords in 1990 by the New Zealand zoologist Ken Grange. It is normally found at 30–40 m, but in Doubtful Sound it grows at just 10 m, within reach of recreational divers.
The coral grows slowly. Colonies are not sexually mature until they reach 0.7–1.0 m tall, at an age of at least 30 years, and a female colony then releases between 1.3 million and nearly 17 million eggs a year. Its branches carry a partner, the snake star Astrobrachion constrictum. The snake star takes a share of the prey the coral’s polyps catch and keeps the branches clean in return. Much of this is protected in the Taipari Roa (Elizabeth Island) Marine Reserve, 613 hectares around Elizabeth Island established in 2005. Its western side is a steep rock wall, its southern side has deep kelp beds, and the shallow eastern channel holds black corals, red corals and zoanthids.
Fur Seals, Crayfish and Whales at The Gut
Towards the sea, the sound narrows between Bauza Island and Secretary Island into a passage known as The Gut, officially Te Awaatu Channel, only 200 m wide at its narrowest. The water here is shallower and more sheltered than further west. It is a popular mooring and fishing spot and a haven for crayfish (rock lobster). The 93-hectare Te Awaatu Channel (The Gut) Marine Reserve, set up in 1993, is the smallest marine reserve in Fiordland and one of the oldest. Strong tidal currents run through it, and around it lies Fiordland’s deepest basin, about 420 m down.
The outer sound is also where larger animals turn up. New Zealand fur seals, kekeno, haul out on the rocks; adult males average about 126 kg, while females weigh 30–50 kg. Humpback whales are the most frequently seen whales, followed by southern right whales, and minke whales, sperm whales, orcas, long-finned pilot whales and some beaked whales have also been recorded. At the confluence south of Secretary Island five bodies of water meet: the seaward Gut, Thompson Sound, Bradshaw Sound, the main fiord continuing to Deep Cove, and First Arm. Many features around the entrance carry Spanish names, such as Febrero Point, Pendulo Reach and Malaspina Reach. They date from February 1793, when Alessandro Malaspina’s expedition anchored here to measure gravity with a pendulum.
Secretary Island and Bauza Island: Pest-Free Refuges for Native Birds
Secretary Island (Ka Tū-waewae-o-Tū) forms the northern shore of the outer sound. It covers 81.4 km² of steep, bush-clad terrain and rises to Mount Grono, 1,196 m, which is the highest peak in the main New Zealand chain outside the North and South Islands. Possums and rodents never reached it, so mistletoes and mountain lancewood that possums have stripped elsewhere still flourish. The Department of Conservation ran a project from 2004 to 2008 to remove the last two pests, deer and stoats. More than 700 deer were estimated on the island as recently as 2006, and the eradication left only a handful. By 2007 the island was regarded as the largest pest-free island in New Zealand, and it shelters Fiordland crested penguins, New Zealand falcons, kākā, kiwi and kākāriki.
Bauza Island (Mauikatau), just to the south, is much smaller. It is named after Felipe Bauzá, the Malaspina expedition’s cartographer. The only pest ever to reach it was the stoat, and a trapping campaign between 2002 and 2004 using more than 40 traps along the main ridge cleared it. It is one of only nine islands in the Fiordland region with no animal pests. The traps are still checked, because stoats can swim more than a kilometre.
Beech Forest, Waterfalls and 3,000–6,000 mm of Rain
All of this depends on rain. Doubtful Sound receives an average of 3,000–6,000 mm a year, and Deep Cove about 7.6 m. The steep catchment is cloaked in dense native rainforest dominated by southern beech (Nothofagus), with an understorey of shrubs and ferns such as crown fern (Blechnum discolor). The surrounding peaks reach 1,300–1,600 m, and in wet weather hundreds of waterfalls pour off them. The Browne Falls fall more than 600 m, and Helena Falls drops into the sound at Deep Cove. That run-off feeds the brown surface layer that makes the shallow black coral possible.
Deep Cove and the Manapōuri Tailrace
The one big human change to the sound’s water arrives at Deep Cove. The Manapōuri Power Station, completed in 1971, uses the 230 m drop between Lake Manapouri and the sound. Its water leaves through two 10 km tailrace tunnels and pours into the head of the fiord. A second tunnel, finished in 2002, cured a friction problem that had held output to about 585 MW for 30 years; installed capacity is now 854 MW, although resource consents cap output at 800 MW. That makes it New Zealand’s largest hydro station. While the first tunnel was being dug, the former trans-Tasman liner Wanganella was moored in the sound from 1963 to 1969 as a workers’ hostel.
The discharge is clear lake water rather than tannin-stained run-off. It lets more light into the lower layers and changes the thickness of the Low Salinity Layer, which has affected plants and animals in the inner sound. It remains one of the suspected factors in the dolphins’ decline. The plan to raise Lake Manapouri provoked the Save Manapouri Campaign, one of the foundations of New Zealand’s environmental movement.
Today the road over Wilmot Pass still links only the power station with Deep Cove, which is why the sound is so much quieter than its northern neighbour. To see how it compares with the fiord at the end of State Highway 94, read our guide to Milford Sound. For the wider region, including Lake Manapouri and the other sounds, see the Fiordland guide, or find out where both sit among the largest fjords in the world.