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Milford Sound / Piopiotahi is the best known of the fiords in Fiordland. Back in the 1820s vessel captain John Grono, who saw similarities to Milford Haven in Wales, named it.
Recognizing the uniqueness of the underwater habitat, the Piopiotahi / Milford Sound marine reserve was established in 1993, was one of the first reserves in Fiordland and covers an area of 690 hectares along the northern side of the Milford Sound. The Maori name Piopiotahi translates to: "one piopio bird". The piopio was a ground feeding native thrush that is now extinct.
Milford Sound is proclaimed as the "8th wonder of the world" and with its majestic features like the loftiest sea-cliffs in the world, the strikingly shaped Mitre Peak that rises straight from the waters edge to 1,683m and its several spectacular waterfalls surrounded by densely covered native forest this is no coincidence.
The magic on the surface doesn't stop underwater. The fresh water coming down from the mountains absorbs tannins from the forest floor, which stains the water to the colour of tea. Once the fresh water reaches the ocean, it sits as a thick layer on top of the salt water, therefore creating a tea-stained layer that acts as a light blocker and animals that normally inhabit deeper, darker waters, can live in Milford Sound in much shallower depths.
The most well known species that makes Milford Sound diving unique is Black Coral.
Fiordland has one of the world’s largest populations of black coral trees (about 7 million colonies) with some of them up to 300 years old. Normally they live between 200m – 1000m depth, where in Milford Sound they can be found as shallow as 10m deep. Despite their name the trees are actually white, only the skeleton is black, however the trees appear white as they are covered by a thin layer of pale living tissue that connects millions of tiny individual white polyps of only 1mm in size.
The same theory counts for red coral a protected species, that is actually a hydrocoral made up of separate individuals, each with its own feeding and defence system. Usually hyrdrocorals grow only in the deep ocean, but in Milford Sound they can be observed from depths of 15 metres.
Another special group of creatures found in the fiords are the brachiopods, or lamp shells, clam-like animals that are sometimes called ‘living fossils’, as they are among the oldest groups of hard-shelled organisms, dating back more than 500 million years.
Many other animals and organisms call Milford Sound home, there are the ever present butterfly perch, that love the shelter which the black coral trees supply amongst spiny dog sharks, wrasses, blue cod, jock stewarts, tarakihi, octopus, crayfish, sea dragons, tubeworms, sponges and sea squirts, just to name a few.
Looking close at the wall or on the coral trees you might spot nudibranchs in vivid colours and various species of seastars like featherstars, buiscuit stars, brittle stars, snakestars, eleven-armed starfish.
The New Zealand fur seal inhabits Milford Sound and are often playful and curious to see where the divers bubbles come from. Bottlenose dolphins occasionally visit the sound, and the rare Fiordland Crested Penguins, can be observed on the shores of the Sound.