Cruise Day 3: Doubtful Sound

Doubtful Sound / Patea is a very large and naturally imposing fiord which takes second place after Milford Sound as New Zealand's most famous tourism destination.

At 42 kilometres (26 mi) long, Doubtful Sound is the longest, and with a depth of up to 421 metres (1,381 ft) also 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.

Like most of Fiordland, Doubtful Sound receives a high amount of rainfall, ranging from an annual average of 3 to 6 metres (10 to 20 feet).  The vegetation on the mountainous landscape surrounding the fiord is dense native rainforest.

Doubtful  Sound was named 'Doubtful Harbour' in 1770 by Captain Cook, who did not enter the inlet as he was uncertain whether it was navigable under sail.  It was later renamed Doubtful Sound by whalers and sealers.

Doubtful Sound on a clear day

Doubtful Sound lies deep within the Fiordland National Park, about 50 kilometres (31 miles) from the nearest inhabited place, the small town of Manapouri, and is surrounded by mountainous terrain with peaks typically reaching 1,300–1,600 metres (4,300–5,200 ft). Along the coast, there are no settlements for about 200 kilometres (120 miles) in either direction.

Charles Lyttleton, Governor-General of New Zealand (1957-1962) wrote about this part of Fiordland:

"There are just a few areas left in the world where no human has ever set foot. That one of them should be in a country so civilized and so advanced as New Zealand may seem incredible, unless one has visited the south-west corner of the South Island. Jagged razor backed mountains rear their heads into the sky. More than 200 days of rain a year ensure not a tree branch is left bare and brown, moss and epiphytes drape every nook. The forest is intensely green. This is big country... one day peaceful, a study in green and blue, the next melancholy and misty, with low cloud veiling the tops... an awesome place, with its granite precipices, its hanging valleys, its earthquake faults and its thundering cascades."

Doubtful Sound (like many of the fiords in the area) is unusual in that it contains two distinct layers of water that scarcely mix. Depending on rainfall the night before, the top 2–10 metres (5ft – 35 ft) 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 water above is a layer of warmer, heavy, saline water from the sea. 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, 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.

Doubtful Sound on a typical day!

The catchment basin of Doubtful Sound is generally steep terrain that is heavily forested except for locations where surface rock exposures are extensive.

As well as bottlenose dolphins, fur seals, penguins, right whales and humpback whales, the fiord is also home to minke whales, sperm whales and even giant beaked whales.  Orcas (killer whales) and long-finned pilot whales can be found too.

The sound has been identified as an Important Bird Area by Birdlife International because it's 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.