The big blue banquet
At sea, the feasts are grand and impromptu—and everyone’s invited.
It begins with the dolphins. A school of striped commons in grey and gold, swimming in purposeful array. When they find the fish—the anchovies, the pilchards—they whistle to each other down the line, leap from the water, swim closer together, begin to gather the small fish into a ball of glistening bodies.
They’re being watched. Gannets leapfrog in front of the approaching pod. The birds are casual, bobbing about on the water, but alert for signs the dolphins have found something. A couple of sentries 20 metres up in the air are the first to spot the bait ball, brought within reach by the circling cetaceans. The instant the first gannets begin to dive, the rest of the flock rise from the surface, then plunge one by one through the school, each bird calibrating the speed of its plummet to the depth of the fish below, the sun glinting off their snowy feathers, and their dives weaving a tapestry of foamy, turquoise trails through the clear water.
Now everybody knows about it. Large shearwaters—flesh-footed, sooty, Buller’s—are drawn into the melee. Little fluttering shearwaters dip their beaks below the surface to grab plankton brought up by the rising ball of fish. The even tinier storm petrels and little blue penguins hang back on the outskirts, where they’re less likely to be taken out by a tumbling gannet with no regard for anything but its prey. Scavengers descend, looking for scraps: red-billed gulls, black-backed gulls, black petrels. They’ll steal fish right from the mouth of another bird. Far below, a mako circles, perhaps a marlin, even a massive oceanic
In these moments a community is formed, dynamic and ephemeral. The boundary between water and air is transcended; a ballet plays out in three dimensions and in two worlds at once, from 20 metres above the surface to 20 metres below.
The choreography and the dancers differ subtly each time, but the patterns are familiar. Deep-diving gannets scatter the fish, and the dolphins herd them back into a ball. Smaller birds skitter over the water. Eventually, the prey become too spread out, or there’s no longer enough of them to be worth the predators’ while—or else a Bryde’s whale comes lunging in side-on and swallows the entire school in one enormous gulp.
The birds sit back down, preening. The fish and the dolphins disperse. It’s over.
Scientists call these events “multi-species foraging associations”, and they have identified at least eight different kinds in Auckland’s Hauraki Gulf alone. Colloquially, they’re known as work-ups or boil-ups, and they are a familiar sight to anyone who’s been out in a boat or lives near the coast in northern New Zealand. Work-ups are integral to the ecosystem, a vitally important feeding opportunity for dozens of marine species, and a dramatic evocation of the ocean’s mauri.
Once, they stretched for acres across the sea in an unbroken froth of vitality and abundance. Now, they are smaller and fewer. We know so little about them, and the tools necessary for studying them have only just been invented. Scientists are racing to understand how these natural wonders start, why they end, who’s involved, and the role they play in the coastal food web—while they still happen at all.
“I definitely have envy for people who study something that they can put in a box or in an aquarium,” says University of Auckland marine biologist Rochelle Constantine. Dressed for action in waterproof overalls and a cap that clips onto her ponytail, she almost has to shout over the engine noise of the university boat as it speeds out of the harbour at Leigh and turns right towards Sandspit.
The direction is arbitrary. Constantine and her team are hoping to find work-ups, but can’t yet reliably predict where they’ll be. Instead, they have to motor around the ocean looking for them. On some trips—part of a project called “Pulse of the Gulf” that aims to map the Hauraki Gulf Marine Park’s ecosystem in more detail than ever before—the scientists can go for hours seeing nothing but one little blue penguin and a couple of gannets. “You go, ‘Where is everyone? Are they just tucked in somewhere else? Have they moved out?’” says Constantine. “We don’t know.”
But today, the researchers are in luck. Between Tāwharanui Peninsula and Kawau Island, sharp white wings flash against the water, and the surface ripples with fish. Instead of dolphins and gannets, it’s another kind of feeding aggregation commonly found in the Hauraki Gulf—a community of white-fronted terns, fluttering shearwaters, kahawai, and plankton.
[sidebar-1]“I’m really interested in knowing who moves first,” says Constantine. “Are there certain individuals who are catalysts, or is it driven by a numbers game? For example, can you only ever have a maximum of 60 terns and 100 shearwaters when there’s this much kahawai? If the kahawai school is smaller, do you have fewer birds? It’s just trying to understand those dynamics of the community.”
Skipper Boyd Taylor brings the inflatable to a stop around 100 metres away, and technician Esther Stuck sends up a small drone. “Keep going left,” says Constantine, guiding Stuck to the action. “No, other left—there. Go up to 50 metres and tell me when you’ve got them.” On the screen of Stuck’s handset we can see the sinuous silhouettes of the kahawai, and a bird’s-eye-view of the seabirds wheeling above them.
Each species plays a crucial role, Constantine explains. Although the fish and the birds compete for access to the plankton, they also help each other. “The kahawai push the larval fish to the surface, then the little white-fronted terns can plop down and pick them up,” she says. If the kahawai drop down, the little fish move out of reach, and the terns fly high to see where the kahawai go next. The association is so strong that white-fronted terns are often called “kahawai birds”.
Then she points out the little fluttering shearwaters, ungainly compared with the terns’ sleek grace. “They’re not really built for flying,” Constantine says. So, while the terns watch the kahawai, the shearwaters wait on the surface and watch the terns for cues. When they see them flying high and looking down, locking their eyes on the school below, the shearwaters know the kahawai must be close, so they shuffle into the space between, waiting for the fish to drive the plankton into their waiting beaks.
Wednesday Davis’ love of the sea was fostered by her Grandma Janet, an early scuba diver, citizen scientist, and underwater photographer who explored Tauranga’s moana alongside her husband, Harold, starting in the 1960s. Davis grew up listening to her stories, poring over books by Jacques Cousteau and Wade Doak, and dreaming of becoming a marine scientist.
Now 24, she’s just completed a master’s degree at the University of Auckland—supervised by Constantine—focusing on the dynamics of work-ups in the Hauraki Gulf. During the course of her research, Davis reckons she’s seen about 100 of them, sort of, with her own eyes. While it’s possible to observe the animals’ behaviours unfold from a bobbing boat, she says the advent of drones and artificial intelligence has completely changed the game.
Cameras mounted on drones flying at 30 metres above the surface of the water can see things boat-bound humans can’t, like the distinctive torpedo shapes of the kahawai as they herd the plankton within reach of the birds. That’s how the scientists discovered the predictable way the shearwaters follow terns following kahawai.
“We were only able to see that following pattern with the drones,” Davis says. “From the water, we thought they might be following fish, but now we’ve got hard evidence.” The scientists’ eye in the sky can’t always capture the entire work-up—the activity sometimes extends much further than can be seen in the viewfinder—but the drone can record a detailed aerial view of the action that the researchers can analyse later.
In the future, as drone technology and battery life improve, the scientists could send unmanned drones out into the gulf to scan for work-ups and record them. That would provide the first ever empirical data on where, when, and how often they’re happening, and how that is changing over time.
When the first waka nosed into the Hauraki Gulf’s pristine waters, the crew were probably greeted by vast and riotous work-ups—myriad diving gannets and terns, huge pods of hunting dolphins, the sea roiling with fish. In fact, the Polynesian ancestors of Māori were guided to Aotearoa in the first place by migrating seabirds and ocean creatures, says Laurie Beamish, a fisher, voyager, and Ngāi Tai kaumātua who lives overlooking the sea at Umupuia Beach near Maraetai, east of Auckland. “Our waka hourua were quick enough under sail to keep up with the migrating whales and rays, and to follow the manu on our sea passages,” he says. “There was definite migration along those pathways—all following the work-up.”
Many iwi tell stories of rangatira travelling with seabirds. Ngāi Tai—one of the first peoples to settle in the Hauraki Gulf—tell of the ancestor Manawatere landing at Auckland’s Cockle Bay on the back of a taniwha called Huruhurumanu, meaning the feathered bird.
Later, when the Tainui waka arrived, they anchored near Umupuia in an area described as having “many terns”. They followed the birds west to the Manukau Harbour, Beamish says, where the fish were so abundant the tohunga Taikehu was able to catch jumping kanae (mullet) with his bare hands. On the Waitematā, Taikehu’s people were soon so numerous on the water that a whakataukī ties their identity directly to the ubiquitous marine life they fished for: Ngā waka o Taikehu me he kāhui kataha kapi tai / The canoes of Taikehu, like a shoal of herrings filling the sea.
One Māori word used to describe the phenomenon of work-ups is tararukuruku, Beamish says, which refers to the flipping of a seabird’s tail just before it dives. The birds’ behaviour wasn’t just observed for navigational purposes, but for fishing as well. “It’s always been a key indicator, a tohu,” says Beamish.
Earlier in life, when he worked as a commercial fisherman, Beamish looked for gannets and dolphins to find yellowfin tuna. Now, he fishes customarily for his marae. “When people try to prise my prized fishing spots from my brain, I always say, ‘Stop at the second penguin.’ They think I’m joking!” he says. But it’s not far from the truth. When he fishes, he pays close attention to what the birds are doing—they act like neon lights, he says, saying, “Hey, what about over here.”
The earliest Pākehā fishermen soon learned to follow the birds as well—though back then, they barely needed to. In an 1853 handbook on New Zealand for aspiring emigrants, colonial administrator George Butler Earp observed that the harbours of the Hauraki Gulf abounded with fish. “Abound is a poor word for it: they are literally alive with fish… On a sunny morning the surface of the harbour is a complete mass of fishy life.”
In 1925, the American writer and pioneering game-fisher Zane Grey visited the Bay of Islands, the following year writing up a lurid account of his travels called Tales of the Angler’s El Dorado: New Zealand. Grey described “flocks of small white black-headed gulls”—clearly white-fronted terns—flying above a school of kahawai an acre across, “sometimes alighting on the water, in the thick of the schools, evidently feeding on the tiny minnows the kahawai were chasing”.
Grey admired gannets diving for fish in water just a foot deep—“I doff my hat to you, Mr. Gannet,” he said, literally raising his hat in the bird’s direction—and described a sooty shearwater swimming right up to the boat, so tame and unafraid that a crew member could pick it up with his bare hands and set it on the deck. Grey soon learned that where there were work-ups, there were also swordfish—the animals he had come to hunt. Everywhere he went along the Northland coast—the Cavalli Islands, Cape Brett, the Poor Knights—he found huge accumulations of fish and birds.
“The white gulls, like showers of feathers, were now rosy in the sunset glow. They ascended to fly over the frothy patch of water where the trevalli [sic] roared like a running brook, and screaming, they alighted amidst the school… The air was full of moving fluttering specks of white. Crash! Another great swordfish had smashed at the school,” he wrote, in characteristic purple prose.
“Then the …trevalli, a creeping acre of white seething foam, burst into a crashing splash… The battle went on. It was life and death, something vital, beautiful, inevitable and unquenchable, and at the same time sinister and tragic. The black mystic waters rolled over this hidden reef and the inexplicable nature of the deep… As we sped away over the darkening sea… I watched the white gulls hovering and wheeling in the strange afterglow of light.”
The abundance Grey witnessed was still barely diminished a generation later.
In interviews carried out in the 1990s and analysed by NIWA, one person reported standing on the shore of Aotea/Great Barrier in the 1960s and seeing 20 schools of kahawai, each an acre in size. Another remembered the island’s Tryphena Harbour in the 1950s being “thick” with birds in the summer; “the whole bay was just about covered with shoals of kahawai.”
When did it all change? As no-one has empirically studied the phenomenon before, there’s little hard data. But anecdotal evidence suggests that by 1993, when those interviews were carried out, people had noticed a dramatic decrease in the frequency and size of the work-ups. Their role in animals’ lives must therefore be changing, says Davis. “They’re still very important events, but they’re very much impacted by the health of our ecosystem.”
Beamish blames the 1970s advent of purse-seine fishing—where entire schools of fish are encircled in a large, vertical net—for the decline. The technique helped to drive the commercial catch of kahawai in northeastern New Zealand from a few hundred tonnes to a peak of nearly 4300 tonnes in 1988 (under the quota system, it’s now capped at around 1000 tonnes.) “The mile upon mile of pelagic fish that were present prior to the purse seiners arriving, it was just chalk and cheese, night and day compared with now,” says Beamish.
Fewer trevally, tarakihi and kahawai in the ecosystem makes life harder for many seabirds, says Constantine.
“If we’re losing those big predators, those big fish that bring the prey up, there’s a reduction in the food available—which is very important when you’re a little bird in the big ocean.”
Another possible factor is a collapse in the numbers of small fish like anchovies and pilchards, often called “bait fish”, though Constantine despairs at the name: “That does my head in—it’s not just bait, it’s actually really important food for lots of animals. Bigger fish eat them, sharks eat them, dolphins eat them, gannets eat them, whales eat them—and they’re a high-value nutrition item as well.”
In the 1990s, a mystery virus imported in fishing bait from Australia decimated New Zealand’s pilchard population. Australian scientists described the disease fronts there moving with the speed of a bushfire, even against the current—spreading up to 40 kilometres per day. Here, the virus left pilchards dead in their millions, strewn across the surface of the gulf, and their numbers have never recovered. While there have been no fish-stock assessments or biomass estimates done for either anchovies or pilchards in decades, experienced commercial fishers report that both species are much less plentiful than they once were—with consequences for the many other animals that depend on them.
Constantine’s team has already observed a change in the diet of Bryde’s whales over the past decade. Tagging studies showed they used to eat mostly fish, things like anchovies and pilchards, which they would catch by lunging out of the water on a 45-degree angle. Now, the whales mostly eat zooplankton—tiny larval fish—using a different technique: slapping their chins on the surface of the water and lunging sideways.
“There was a community of birds in particular that were associated with those fish-feeding whales, and that community is now pretty much gone, because the whales have changed their diet,” Constantine says. “So whether [the birds] were using the whales as a cue to find fish, we’re not sure. It’s all over now, so we won’t know.”
Climate change adds another stressor, she says. “We’re going into our third La Niña in a row. That’s a really big problem.” Warmer waters tend to push plankton further offshore, drawing dolphins and whales and other predators with them. That could be too far to travel for birds that nest in the inner gulf. “Will they move their nesting sites, or will they move their core habitats? These are birds on the edge, and it’s not easy for them in times like this.”
Out on the university’s boat, we find another small cluster of terns and shearwaters near the south end of Kawau Island. Above, the clouds line up in puffy streaks of scalloped scales, a formation sometimes called a “mackerel sky”. But below, the fish we glimpse breaking the sea’s surface are kahawai, of course.
Stuck sends up the drone, and this time, Constantine directs Taylor to drive right through the middle of the work-up. I look over Stuck’s shoulder as the drone records what happens. Terns scatter as the boat approaches, and panicked-looking shearwaters bustle out of the way.
Recreational and commercial vessels alike will often mow straight through a work-up, Constantine says.
“In some of the really busy pathways, especially for recreational boats, you’ll often find a lot of dead birds floating on the water, because people just don’t slow down.” We’re not going fast enough to hurt any birds, though. This experiment is about collecting empirical data on the disruption’s impact on their ability to feed.
“All of those animals are working so hard to find their prey, and to get enough food. If they can’t get enough, then they’re not in good body condition to lay an egg or feed a chick or to get to the next spot. It really matters to these little birds—physiologically, a lot of these animals are right on the edge of living and dying a lot of the time.” Follow the birds to the fish, sure, she says—but don’t get in their way.
“These communities are really ancient. These animals have been aggregating long before humans ever arrived here—for tens of thousands of years, in some cases. I just really want people to understand that there’s probably a consequence if we disrupt them.”
When we do leave the ocean alone, Tangaroa resurges. Laurie Beamish, at home like everyone else during the first COVID-19 lockdown in March 2020, one day noticed an unusual roaring noise disturbing the quiet. There was no traffic, no planes, no boats out, so he and some others from the marae went out to investigate.
The noise was coming from the beach, and it was made by hundreds of fish and birds. Kahawai were chasing the bait fish almost onto the shore, and seabirds were feeding as far as the eye could see, all the way out to Waiheke Island. “It was incredibly loud,” Beamish says. “We hadn’t seen it like that for decades, and we haven’t seen it since.” A tohu indeed.