Moana Uta (Wet Jacket Arm)

Moana Uta (Wet Jacket Arm) Marine Reserve protects about 20.07 square kilometres (2,007 hectares) of deep, sheltered fiord water in Wet Jacket Arm, an inner branch of Dusky Sound/Tamatea within Fiordland, in the remote southwest of New Zealand's South Island. ^[1] Established in 2005 as one of eight Fiordland marine reserves created following a collaborative process led by the Guardians of Fiordland's Fisheries, it is managed by the Department of Conservation. The reserve safeguards the distinctive deep-fiord environment, where a layer of dark, tannin-stained freshwater overlies clear seawater, creating unusual conditions that allow deep-water species to live at unexpectedly shallow depths. Its isolation deep within Fiordland National Park makes it one of the country's least disturbed marine areas.

The reserve's fiord walls and basins support a rich marine community adapted to its unusual low-light conditions, including black coral colonies, sea pens, brachiopods (lampshells), snake stars and diverse encrusting invertebrates that elsewhere live only in much deeper water — the combination of steep rock walls, deep basin, and heavy mountain shading produces the highest known density of black coral at any site in the fiords. ^[1] Reef fish such as blue cod, scarlet wrasse, telescope fish and tarakihi inhabit the rock walls, while rock lobster shelter among crevices. The surrounding waters of Dusky Sound host New Zealand fur seals, Fiordland crested penguins (tawaki), bottlenose dolphins and a variety of seabirds.

The dark freshwater layer that caps the fiord limits light penetration, so attached seaweeds are sparse near the surface, and the rock walls below are dominated instead by invertebrate communities. Where light allows, kelp and red algae grow in the shallow margins, with subtidal rocky reefs supporting dense beds of kelp and notably low kina populations. ^[1] Above the waterline, the steep slopes of Fiordland National Park surrounding the reserve are clothed in dense temperate rainforest of silver beech, southern rātā, kāmahi and a luxuriant understory of ferns, mosses and liverworts, clinging to near-vertical rock and contributing the tannins and freshwater runoff that shape the fiord's marine environment.

Wet Jacket Arm lies within Fiordland's deeply glaciated landscape, carved by successive ice ages into steep-sided, U-shaped troughs that were later drowned by the sea to form fiords. The underlying rock is hard, ancient crystalline basement of gneiss and granite that resists erosion, producing sheer underwater walls dropping into deep basins. The high rainfall of Fiordland delivers vast amounts of freshwater that floats atop the denser seawater, and the dark, tannin-rich runoff staining this surface layer is fundamental to the reserve's unusual ecology, allowing deep-water species to thrive close to the surface.

Fiordland has one of the wettest climates in New Zealand, with extremely high annual rainfall driven by moist westerly winds rising over the mountains. The reserve experiences cool temperatures, frequent rain, low cloud and rapidly changing conditions year-round. This abundant rainfall is essential to maintaining the freshwater layer over the fiord. Sea temperatures are cool, and the sheltered inner arm is calmer than the open coast, but access remains weather-dependent and challenging. Calm windows for boating and diving are most likely in settled summer periods, though heavy rain can occur in any season.

Dusky Sound/Tamatea holds significant history for Māori, particularly Ngāi Tahu, who travelled the Fiordland coast seeking pounamu, kaimoana and other resources, and the broader area carries many traditional names and associations. Dusky Sound was a focus of early European contact, with James Cook making an extended stay there in 1773 during his second voyage, the first prolonged European visit to New Zealand's southwest. The sound later saw sealing and whaling activity. Wet Jacket Arm and the wider fiord have remained largely uninhabited, valued for their wilderness character within Fiordland National Park.

Moana Uta (Wet Jacket Arm) Marine Reserve was established in 2005 as one of eight marine reserves created across Fiordland following a collaborative process led by the Guardians of Fiordland's Fisheries, working with local communities, fishers, tangata whenua and government agencies. ^[1] This integrated approach combined no-take reserves with wider fisheries management to protect Fiordland's exceptional marine values. The reserve was chosen to safeguard a representative example of the deep, sheltered inner-fiord environment and its unusual emergence of deep-water species, contributing to one of New Zealand's most comprehensive regional marine protection frameworks.

The reserve has no land trails and is valued instead for its underwater environment and wilderness setting. For the few who reach it, the main attraction is diving among black coral and other normally deep-water species found at accessible depths beneath the freshwater layer, a phenomenon unique to Fiordland's fiords. The dramatic scenery of Dusky Sound, the surrounding rainforest-clad cliffs, waterfalls and wildlife including penguins, seals and dolphins are major draws. Wet Jacket Arm forms part of the remote Dusky Sound/Tamatea area celebrated for its historical and natural significance.

Access is extremely remote, with no roads, facilities or settlements nearby; the reserve is reached only by boat through Dusky Sound or by floatplane, typically via multi-day expeditions or specialist charters. ^[1] The nearest town, Te Anau, lies about 80 kilometres away across mountainous wilderness. Visitors must be fully self-sufficient and prepared for demanding, weather-dependent conditions. All fishing and removal of marine life within the reserve are prohibited. Because of its isolation within Fiordland National Park, visitation is limited mainly to experienced boaters, charter operators and divers.

As a no-take marine reserve, Wet Jacket Arm is protected from fishing and any extraction of marine life, preserving its fragile black coral and deep-water invertebrate communities that are slow-growing and highly vulnerable to disturbance. ^[1] It forms part of an integrated Fiordland marine management regime that pairs reserves with sustainable fisheries rules and strong community and iwi involvement. Conservation priorities include preventing sedimentation, protecting water quality and the freshwater layer, and guarding against marine pests introduced by visiting vessels. Its remoteness and full protection make it an outstanding refuge for Fiordland's distinctive marine ecosystems.