What we do in the shallows
The ocean is our playground, storehouse, transport corridor, driver of weather and coastal change. We’ve learned the hard way that it’s possible for us to exhaust its resources and overwhelm its natural processes. Now, scientists are mapping the web of relationships between the sea, the land and human industry, to figure out how fishing, aquaculture, tourism, land development, and recreation affect its health. What should be permitted, and what prohibited—and where? How can we best strike a balance between using and protecting our seas?
The first time Bill Moore dropped a scallop dredge in Golden Bay, just a short distance out from the curving twin wharves of Port Tarakohe, it came back so heavy with scallops that he could barely lift it over the side of the boat. It was the early 1990s, and the seabed below the surface was a city of scallops, their delicate creamy-pink fans hiding the sweet, tender flesh and roe within.
“It was always a treat to take someone out and see their eyes pop when they saw the dredge coming up,” says Moore. His favourite way to eat them is raw, fresh out of the shell with a daub of soy sauce, preferably while standing in the water.
There were a lot of good years like that, his boat floor covered with dozens and dozens of big, dripping shells. But then Moore, who is a former fisheries reporter and editor of the Nelson Mail, began to notice the decline. Scallops became scarcer, and it was increasingly difficult to get enough to fill the quota. The last couple of times recently he’s gone out scalloping, he’s got nothing.
“It’s a tragedy,” he says. “It was a great treat to be able to motor out into Tasman Bay and come back with a feed of scallops, with enough to give some away to family.”
He’s already seen the scallop industry collapse and recover once since he began at the Nelson Mail in 1984. The highest catch ever recorded was in the gold-rush days of 1975, when 1246 tonnes of scallop meat was hauled out of the ocean. By 1980, that had plummeted to 41 tonnes, and the government closed the fishery.
A tight management regime and a seeding programme that spread 10 million spat each year between 1984 and 1987 helped stocks to recover. Yields were generally robust in the 90s, and in 1992, 48 licence holders were allocated a fixed annual catch of 12 tonnes each, with 64 tonnes allocated to Māori, and more allocations were available each year. Thus came another gold rush. Between 1991 and 2002, the commercial catch was as much as 684 tonnes. The best seasons added more than $25 million to the regional economy’s coffers, and even the worst season brought in 231 tonnes.
It wasn’t to last. In 2015, the catch was down to 22 tonnes, and the Ministry for Primary Industries (MPI) closed the fishery—incorporating the Marlborough Sounds, Tasman Bay, Port Underwood, and Golden Bay—for the following season. When surveys showed that scallop biomass had dropped between 2015 and 2017, even with the catch ban, it stayed closed.
This time, it doesn’t seem to be recovering. Whatever is damaging the scallop beds may have reached a tipping point from which the scallops can’t recover—meaning the death of the fishery forever.
No one knows exactly what has caused the collapse, but an MPI discussion document says it’s probably a combination of sediment, climate and weather effects, primary production and fishing, disease, toxins and pollutants. Some fishers blame ocean-floor dredging, which is partly a recreational activity, but mainly a commercial one.
One of the clues is a half-metre layer of fine silt suspended above the sea floor of Tasman Bay. Sediment chokes the scallops, which, like many other bivalves, feed by filtering food from the water. The murky layer is deadly to them, and affects other marine organisms, which rely on a firm, clear seabed. (Green-lipped mussel and oyster fisheries in Nelson and Tasman Bays have separately crashed in the past 50 years.)
New Zealand has a naturally high rate of sediment run-off—the country is tectonically and volcanically active, with short, steep catchments and changeable, sometimes violent weather. But humans have radically changed the landscape, and as primary production has increased over the past century, the coast is having to deal with more change than it evolved to absorb. And now there’s climate change to consider, too.
Tasman and Golden Bays are bordered by plains and hills covered in horticulture, agriculture, and forestry, dotted with towns housing 100,000 people, and streaked with rivers that regularly swell in flood, bringing copious amounts of material down from the rugged mountain ranges that encapsulate the bays. But all this activity—along with fishing, water recreation, and tourism—takes place in two confined spaces, and the two bays have had to absorb the effects of increasingly complex land uses. They’re excellent areas to use as case studies for a new approach in which New Zealand is leading the world: ecosystem-based management (EBM), which heralds a new relationship with our seas—one where the health and connectivity of every system in this ‘blue economy’ are paramount.
“We’re thinking about helping marine ecosystems but we also need a healthy economy,” says Julie Hall, director of the government’s Sustainable Seas National Science Challenge. “Healthy ecosystems support a strong blue economy and EBM is the tool that will help us achieve that.”
EBM looks at every impact on every system, taking a holistic view of the web of relationships between the natural world, industry and human wellbeing.
One way of understanding it is to compare the ocean to the skin on a human body. Instead of studying and diagnosing problems with the skin by looking at its surface, an EBM approach would consider every possible impact upon it, such as stress, nutrition, pollution, genes, and hormones.
New Zealand may be the fourth-largest country in the world when marine territory is included, but the cumulative effect of what’s happening on land as well as in the water hasn’t traditionally been considered when it comes to ocean health—especially the coastal regions that form the boundary between land and open sea, where we swim, fish, sail and play.
EBM is used in pockets internationally, but it’s never been seen on a countrywide scale, which is the plan for New Zealand. At the moment, we manage individual parts of our coasts and ecosystems in isolation from each other: one estuary, or one fish species.
EBM will provide a much more robust answer to some of our biggest questions: How do we know when we’re affecting the food chain too much? How much run-off and other pollutants can the ocean absorb? How many fish can we take? What are the tipping points? How do we stay within them—and what happens when we go over them?
It’s a change in approach for some fisheries management practices, and it’ll also address other human activities, such as run-off from development clogging up bays, destroying food webs, and depositing heavy metals or sewage-tainted sediment in the sea.
A complex ecosystem is a strong one, and better able to tolerate disturbance. And with climate change and increasing human impact, there’s going to be a lot more disturbance in the future.
The scientists involved are part of the Sustainable Seas challenge, which itself happens to be a kind of whole-ecosystem way of doing science—connecting experts from different disciplines and institutions around the country. Traditionally, New Zealand’s funding system sees scientists compete for limited resources, but the challenge offers the chance to work collaboratively on research projects and contribute to the EBM approach.
New Zealand already has a case study that shows how EBM can improve the health and productivity of a marine ecosystem, and it’s in one of the most iconic and precious areas of our country: Fiordland.
“It was essentially a big regional experiment,” says University of Otago marine science professor Steve Wing, who has been studying the area for more than 20 years and watching how its marine systems have changed. Since 2005, fishing has been controlled by a series of marine reserves, with no-take areas surrounded by zones available for recreational fishing only. These restricted areas have become important refuges for spawning marine creatures such as rock lobsters and blue cod, supplying larvae that support populations up and down the west coast, even into the North Island.
“The results of this have been really positive in terms of fisheries and enhanced biodiversity across the region,” says Wing.
Now, he’s doing similar work for Sustainable Seas, looking at how the different parts of an environment are connected, and how marine ecosystems can be managed more holistically. He’s investigating the trophic structure of fish communities—what food they rely on, and how they provide food for others. How does aquaculture fit into natural food webs? What happens to scallops, oysters and mussels when activities on land flow into coastal waters?
“The reason we’ve chosen these things is that they’re topics that fit into what we think are the most important issues that could guide better management,” says Wing. “They are also vital ecosystem properties that aren’t currently recognised in some of the management that New Zealand does.”
Wing and his team use chemical tracers to follow the path of organic matter and nutrients, the currency of ecosystems, through food webs. Where do nutrients enter an ecosystem—do they come from land, kelp forests, or phytoplankton in the open sea?
By sampling fish, bivalves and other invertebrates, and analysing the chemical composition of their tissues, Wing can draw connections between different parts of the food web.
What’s happening on the land has a large effect on the underwater world. For example, in Fiordland, humus from native bush is an important component of food webs in the sea. One recent study shows that while Fiordland has lush kelp forests, these are less extensive in the Marlborough Sounds, likely as a consequence of increased sediment and increased temperatures.
The result? In the Marlborough Sounds, much less organic matter—much less food for grazing invertebrates—flows from kelp forests into the food webs that help coastal fish populations thrive.
“It shows we need to manage land-based inputs to do a good job of protecting critical habitats like kelp forests,” says Wing.
A related project that the group is doing is to examine all the fish species in the quota management system in terms of their position in the food web and the prey that they rely on—the connections between different species of fish. Then, using chemical analysis of both modern and museum specimens, the team is investigating how the composition of marine food webs has changed over the history of fisheries management in New Zealand.
“We’re trying to quantify those dependencies and connections within marine food webs,” says Wing.
“You don’t have to go far to talk to locals who will tell you stories about how it was different back in the day,” says Simon Thrush, director of the Institute of Marine Science at the University of Auckland. “We are losing things.”
The scallops of Tasman and Golden Bays are just one example. Most New Zealanders who are familiar with stretches of coast will be able to think of others.
Thrush’s team aims to figure out what causes these tipping points—when even subtle pressures on an ecosystem interact and build up so much that there’s a sudden shift, and the ecosystem loses its capacity to absorb changes.
Ecosystems don’t evolve or react to pressures in a linear way, and a tipping point can create not just species loss but also a change in ‘ecosystem services’—processes that keep everything ticking along nicely, such as water purification, or the removal or sequestration of pollutants.
“It’s recognising that surprises can happen,” says Thrush. “It’s not a good place to be, as a resource manager, if you’re at the bottom of the cliff realising you should have stopped at the top.”
University of Waikato biological sciences professor Conrad Pilditch, who is also working on the project, says there’s a lack of fundamental ecological knowledge on how systems are connected across land-sea boundaries, as well as within the ocean.
“The way we have been managing this to date, district councils are often just considering an activity in isolation and not against the background of other activities that are occurring—and it’s not about shutting down activities, it’s considering activities in the context of other ones.”
The project aims to show that marine resources can still be used—they just need to be better managed. Pilditch and Thrush are carrying out an experiment on intertidal flats across 24 sites in 15 estuaries, from Northland to Southland.
Out on the wet sand, they create series of small plots, and increase the nitrogen content of the sediments within each plot. By choosing sites that differ in water cloudiness, the researchers can then tease apart how the sea-floor ecosystem copes with this extra load of nitrogen. Does cloudier water make it more difficult for the ecoystem to cope?
To determine this, researchers monitor the animals and microscopic plants that call the sediments home, and track how they interact. There are a couple of other measures of sediment health, too. How big are the sediment particles? And how much organic matter—a food source—is held within the sediment?
Ideally, the project will give Thrush and Pilditch a sign as to when a sediment ecosystem is becoming overloaded by an acculumation of stressors—in other words, when it’s heading towards a tipping point.
Next, the project will use models to predict what will happen when the amount of light or nutrients in an environment changes, or to forecast trophic cascades.
A well-known example of a trophic cascade is the reintroduction of wolves to Yellowstone National Park. The wolves controlled elk numbers, which resulted in the regeneration of plants and trees, which in turn resulted in more birds and animals and less riverbank erosion. In the ocean, one example is the disappearance of snapper and crayfish, which means there are more kina, which puts more pressure on kelp, and ultimately results in a kina barren.
Wellington Harbour is in the first grip of winter when NIWA marine physicist Craig Stevens leaves on the RV Kaharoa, along with masters student Jorlyn Le Garrec and moorings specialist Mike Brewer. The ship is a 28-metre NIWA vessel built in 1981, and she rocks a bit. But this is a short trip—just four days—and Kaharoa is perfect for this team, testing a new ocean robot for the first time.
After a few delays, thanks to a cranking southerly, and with the first target area spiked by a coming northerly, the team heads south, towards the Clarence River mouth near Kaikōura.
The ocean robot, a Wirewalker, is brand-new technology to New Zealand. It’s about the size of a stubby kayak, shaped like a large yellow pill. It can be configured with different sensors, and once deployed, it ‘walks’ up and down its wire several times per hour, collecting data such as temperature, salinity, speed of the current, and levels of oxygen, nitrates and chlorophyll. On this expedition, the team sets it to measure the top 150 metres of ocean, where most of the surface light and heat are trapped.
Deploying the robot from the ship is a delicate process—it’s not something you can just drop over the side and send on its way. But once it’s working, the Wirewalker captures a very detailed picture of biophysical variation—more than previous methods by a factor of 100 to 1000. Where once Stevens would return from a trip with four profiles from a parcel of water, with this robot the team might be able to come back with 140.
“Normally on a ship, you’d go out and be able to do a few of these profiles in a day amongst the other work,” he says. “What this means is you can drop it off and it can do this grunt-work while we get on with other things.”
How much does it cost? “More than a car and less than a house. Oceanography is incredibly expensive and high-risk, and we have some quite nervous hours, days, months. I call it mooring anxiety. You’ve got a lot of money and investment in the water, which ultimately the taxpayer has funded. We need to have a pretty good reason for why we’re doing it and pretty good processes in place for getting the gear and the data back.”
Technology is driving great leaps in oceanography. For decades, scientists have been fairly limited in how they gather data from the sea and sea floor, but new technology—satellites, drifting samplers, robots, computer models—is helping to collect and analyse vastly greater quantities of data than ever before. Now, technology exists that enables scientists to access ocean robots from their office desk. (As you read this, nearly 4000 autonomous robots are drifting through the world’s oceans right now, taking measurements and calling home every few days.)
Back home, Stevens and the team will use the data to figure out how the ocean mixes and transports material. This involves understanding a number of situations: how heat and energy are dispersed in the ocean, how nutrients mix in a mussel-farm water column, how river plumes get diluted in the sea, and what the effects of all those different actions at different scales can have on an ecosystem.
“We’ve invested the majority of our resources in trying to work out this massive ocean flow that shoots past the mouth of the Tasman-Golden Bay system, and how it exchanges with the bays itself,” says Stevens.
Another part of the research is as simple as a child’s game of Poohsticks—throwing drifters into the water and seeing where they end up. The results can be astonishing.
In one experiment, four drifters left the mouth of the Tasman-Golden Bay system and washed straight out into the South Taranaki Bight. Over the next six weeks, they split up and travelled around the country, from Taranaki to the Chatham Rise. Drifters that started out 30 kilometres apart ended up many hundreds of kilometres apart. Their disparate paths are compared with computer models of ocean mechanics.
“It opens our minds to what reality can do,” says Stevens. “You can see where things have drifted, but it’s also neat to see the little serendipitous events. If one little drifter moves a little bit north and there’s a storm, it will be pushed 100 kilometres away from its buddies, and all that kind of stuff happens differently all the time.”
Coastal areas such as Tasman and Golden Bays, he says, have traditionally been the “interface zone” between our land use and the open ocean.
“Historically, [the ocean] was considered an infinite wastebasket. I think globally we are learning that’s not the case. We have known for centuries that fish stocks are not inexhaustible but it seems we’re only now learning that pollution doesn’t just disappear, it can reappear somewhere else or aggregate in ways that surprise us.”
So what effect will ecosystem-based management have on our use of the ocean? Julie Hall says the research will identify which of our current practices aren’t sustainable in the long term.
That might include recreational and commercial fish take, or tourism businesses spreading pressure elsewhere. Aquaculture may go into deeper, faster-flowing water with stronger currents, or completely offshore.
“I think there’s a wariness from some industries that the end result of what we’re doing may change things for them, but we’re looking for a stable, predictable way to manage things,” she says. “For them to invest, they want stable, predictable management.”
The project is also sparking “a huge amount” of interest internationally, Hall says. One group in Norway is patterning its own research off New Zealand’s.
“There isn’t anybody doing this at the scale we’re looking at. The interdisciplinary work that we’re doing throughout the challenge—drawing in not only social science but also economics, legal and policy, plus mātauranga Māori—is also world-leading.
“Nobody internationally has looked at bringing in ecosystem-based management at the broad national level that we’re looking at with this project. We are not the decision makers, but are providing the underpinning science, information and support, tools and approaches.”
Simon Thrush says even though New Zealand has had environmentally focused policies in the past, implementation of them has been a problem, and it’s led to the degradation of coastal environments—which most of us don’t notice. Few people are lucky to have an intimate connection with the ocean on a timescale long enough to become aware of changes.
“Fishermen do, scuba divers do, but for most of us it’s just the blue bit beside the road as we are driving around the country,” says Thrush.
“While we can look at the landscape and see changes in farming and forestry, we don’t pay so much attention to what’s happening in the marine environment—other than our ability to gather food out of it.”
Science is filling in the gaps, and ecosystem-based management recognises all the different values the ocean holds for different groups.
“What EBM offers is a table where everyone can sit and express their views and values about what’s important about a particular part of the ocean,” he says. “It’s not about one use of the environment taking precedence over others.
“We can keep doing what we are doing and we will keep ending up with a worse and worse situation, and then our option is that we are just going to have to live with it and accept that’s where we are and accept our future options are compromised,” he says. “Or we have to try to do something about it and change our direction.”
With climate change already impacting our land, coasts, and oceans, it could be too late to turn back the clock on what’s been lost for good, such as the bountiful scallops of Tasman and Golden Bays. But as research throws new light on what we contribute to and take from the sea, it could mean that at the very least, such a massive loss might be prevented somewhere else.
This feature was produced in association with the Sustainable Seas National Science Challenge.