Like many New Zealanders, I’ve been collecting Marlborough Sounds vignettes over many years. A wedding in Lochmara Bay when the lodge there was still a backpackers. A field trip to Maud Island where I got my first sniff of kākāpō feathers. A work trip to tour the Perano whaling station with former whalers. And countless long weekends walking or paddling along a labyrinth of secluded coves and inlets—often with no one else in sight.

Domestic tourism has always been an important income-earner for the Marlborough Sounds, bringing in $260 million a year—twice as much as international visitors—even before the COVID-19 pandemic. But to make a living in this vast seascape embraced by frayed scraps of land is less idyllic. The further away people live from Picton and Tōtaranui/Queen Charlotte Sound, the more they rely on fishing, forestry and farming for their income. Each of these has changed the ecology of the sounds, often irreversibly.

Geologically speaking, the sounds are the remnants of a long-lost mountainous landscape: drowned river-cut valleys that began sinking some 1.5 million years ago, pulled down by the friction of tilting tectonic plates. As the ocean inundated the valley floors, it redrew a tenth of New Zealand’s coastline. The islands and ridges rising from the sea today are ancient mountaintops, with slopes so steep in parts that soil is always on the verge of sliding off. There are few places in New Zealand where land and water are so closely entangled. Anything that happens on land affects life in the sea and on the ocean floor.

Māori arrived in the early 14th century, in successive waves of migration. More than 300 archaeological sites have been unearthed in Tōtaranui, including middens, hāngī pits, gardens and fortified pā. These chart the first wave of environmental change, as Māori hunted New Zealand sea lions, southern elephant seals and Waitaha penguins to the point of local extinction, and cut down the population size of New Zealand fur seals.

But they left forests and other marine life largely intact. Fish were still plentiful by the time the Endeavour sailed into Meretoto/Ship Cove in 1770. And when the first whaling ship visited Port Underwood in 1828, the harbour still swarmed with whales en route to their breeding grounds in the sounds. Soon there were six whaling stations and 18 vessels, with many smaller boats chasing each whale. The Marlborough Sounds had produced New Zealand’s first export industry for markets in Europe: whale oil. Just a decade later, the German naturalist Ernst Dieffenbach warned that tohorā/southern right whales would decline rapidly as the whalers were hunting so many mothers and their calves. He turned out to be right.

The disappearance of whales was only the first of several radical transformations.

Historic sediment accumulation, Kenepuru Sound

The number of European settlers increased dramatically from 1860 to 1880, in response to a short-lived gold rush in the Pelorus river catchment, and in pursuit of timber, which was the main method of financing the development of pastoral farms. Timber mills sprang up around the head of the Pelorus River, and Havelock became a timber shipping yard and service centre for gold miners. Gold sluicing and the cutting of old-growth native forests set off erosion and denuded steep hillsides. This started choking waterways with sediment, in a process that continues today as soils are stripped from farmland and blocks of commercial pine forest.

During the early 1900s, a trawling fishery got under way in Cook Strait. Despite calls to ban trawling inside the sheltered waters of the sounds to protect fish breeding grounds, it continued. By the 1970s, blue cod was in decline and a 2010 survey found stocks had dropped by 60 per cent between 1995 and 2007, suggesting localised depletion. Long-term monitoring of all fish netted in a tidal estuary between 1971 and 2004 showed they had become fewer and smaller—there was a 70 per cent drop when measured by the number of fish and a 91 per cent drop when measured by weight.

Dredging quickly destroyed oyster beds in Tory Channel, and green-lipped mussels, once common on the seabed and intertidal reefs, disappeared by the 1960s. A scallop fishery, once the largest in the country, is now off limits.

Locals describe ongoing sedimentation, damage to the sea bed and fishing as their main concerns. “Every time there’s a State of the Environment report released, it’s highlighting further degradation,” says Eric Jorgensen, who’s involved in several local organisations and is a trustee of the Marlborough Sounds Integrated Management Trust. “We’re not halting that, much less turning it around. And we are literally seeing ecosystems collapsing.”

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WHAT WE KNOW

Too much sediment damages life on the ocean floor. Before the arrival of Europeans, the Pelorus and Kaituna rivers flushed sediment into the ocean at an average accumulation rate of less than a millimetre (0.2-1.2 millimetres) per year, occasionally topped up by natural slips.

But sedimentation increased by an order of magnitude (1.8 to 4.6 millimetres per year) when settlers started sluicing for gold and milling timber to clear the land for farming and exotic forestry. According to a study that examined sediment cores in Pelorus Sound, the greatest contributions to sediment flows since 1975 are from land cleared for sheep farming, and from commercial pine-forest blocks following harvest. Although pine plantations cover less than 15 per cent of the study region, most sediment comes from areas that have recently been harvested.

Some marine species have gone beyond their tipping point. Southern right whales/tohorā  used to be semi-resident in the sounds, spending six months there to have their calves. In the northern hemisphere, right whales play an important role in transporting nutrients across vast ocean distances, fattening up in their feeding grounds and then releasing nitrogen and iron-rich plumes of poo into their breeding grounds. This acts as a fertiliser for marine algae. Algal blooms kick off the entire food web in the ocean, and tohorā likely had the same ocean-fertilising role here. They were a keystone species—their presence, and then their absence, had a dramatic impact on the whole ecosystem.

Another keystone species is the pilchard, known locally as the Picton herring or Picton bloater. These small fish eat plankton, and their shoals help sustain kingfish, kahawai and blue cod, as well as dolphins and seabirds. In the 1860s, large shoals could be seen in Tōtaranui during winter when the fish came into shallower water, and big hauls kept four smokehouses going.

In the early 1940s, there were enough fish to supply a pilchard cannery in Picton, but catches dropped quickly from almost 300 tonnes in 1942 to 11 tonnes in 1949. The factory closed. Pilchards are still fished in the sounds, but large shoals are now a rare sight.

Ecosystem builders are missing. Wild green-lipped mussels and kelp are ecosystem engineers—they provide shelter, habitat and food for many other species. They were once thriving in the Marlborough Sounds, but are now reduced in number or completely gone.

Pelorus Sound used to have extensive beds and subtidal reefs of green-lipped mussels. They likely sheltered and fed many fish species, but collapsed after commercial dredging during the 1960s. They haven’t recovered since—and while the reasons for this are complex, the combination of overexploitation at the time and ongoing sedimentation probably stops wild mussels from re-establishing. The Marlborough Sounds are now the centre of green-lipped-mussel aquaculture.

Meanwhile, warming coastal waters and changing predator-prey dynamics are pushing kelp into retreat in parts of Tōtaranui. Pāua like eating kelp, but so do kina—and the latter are part of an ecological spiral in which blue cod eats kina, kina eats kelp, but blue cod needs kelp as a nursery. Seafloor surveys now show extensive kina barrens in Tōtaranui—areas of the ocean floor where there are only kina.

Blue cod assessment, Queen Charlotte Sound

How we fix it

 Reducing erosion has to be a priority. Land erosion and sedimentation affect marine creatures on the seafloor like a chronic illness. Several groups working towards the ecological restoration of the sounds agree the sedimentation problem needs to be resolved first to improve the chances of success for conservation projects such as the reseeding of wild mussels and replanting of seagrass meadows.

Commercial forestry is a significant contributor to soil erosion. Pines were planted during the 1970s and 1980s when the government subsidised small-scale exotic forestry, but even back then, says Eric Jorgensen, people warned that the steep hills of the Marlborough Sounds may not be suitable for them.

In its proposed environment plan, the Marlborough District Council suggests buffer zones and replanting harvested forestry slopes more quickly to retain the soil. But for Jorgensen, that’s not enough—the way we use that land needs to change. “Yes, we need some landcover on there, but it needn’t be more pine. We don’t want to do this every 25 years. Instead, we need to be advocating for a sustainable land transition.”

Jorgensen is also part of the Marlborough Sounds Restoration Trust, which has taken on the monumental task of controlling wilding pines throughout the sounds, from D’Urville Island to the outer Queen Charlotte Sound.

 More marine protection and guardianship. There is only one marine reserve in the Marlborough Sounds, at Kokomohua/Long Island, and it covers less than 0.001 per cent of coastal waters. Pāua and blue cod are noticeably bigger there. The council is compiling a list of significant marine biological sites, and the Guardians of the Sounds, a community group that initially formed to fight for slower ferry speeds to limit damage to the coastline, hope to add an area in Tōtaranui where Hector’s dolphins breed. Eventually, they would like to see this spot protected as a marine reserve.

A group of young women, who started a marine team while at Marlborough Girls’ College, want to take things even further. They met Prime Minister Jacinda Ardern last year to propose a new statutory body of marine guardians, modelled on laws introduced to manage the marine environment in Fiordland and off Kaikōura. The guardians would include iwi, central and local government appointees and community-elected representatives, with an advisory group of people representing different interests in the sounds. Their task would be to draw up a spatial plan to identify areas that need protection as seabed reserves, species sanctuaries, recreational reserves, traditional Māori fishing areas or no-take reserves.

 Make plans with the entire ecosystem in mind. One could argue that earlier generations couldn’t foresee the impact of extractive industries, but Jorgensen says it’s now time for planning and management practices that anticipate change and incorporate the complexity of ecosystems at a much finer scale and with more local knowledge. Such ecosystem-based management is what marine scientists are advocating for coastal environments elsewhere—in contrast to the current approach, which usually focuses on managing single species (fisheries) or single activities (land use) without considering cumulative impacts on the environment and climate.