Peeping in on the Mile Deep Club

Braving an Antarctic winter to catch Chilean sea bass in the act.

Published August 8, 2017

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In the dim light of a polar winter day, a sliding hydraulic wall opens on the fishing vessel Janas, exposing two fishermen on the lower deck to the full onslaught of winds blasting off Antarctica. While the vessel bobs on the frigid ocean, the men, clad in padded yellow coveralls, blue anoraks, and thick, protective rubber boots, peer down into the sea as a winch hauls up a thick metal fishing line. A slate-gray shape emerges from the deep and dangles below—it’s the prize they’ve come for: an Antarctic toothfish.

When it’s swimming free, the Antarctic toothfish is a nimble hunter—a lunging, gulping predator weighing up to 120 kilograms (as much as a baby elephant) with biological antifreeze, a glycoprotein, coursing through its veins. But the mottled creature on the hook is limp and docile after being dragged up from a depth of at least two kilometers. One man reaches down and swiftly stabs the fish’s head using a hooked gaff. His partner skewers it from the other side and together they haul it into the Janas’s factory room.

Antarctic toothfish—known to gourmands as Chilean sea bass—are a lucrative catch and can fetch up to US $50 a kilogram wholesale (consumers pay much more for the oily delicacy in stores and restaurants). The fish caught on this July day is extra valuable though—it’s been snagged in the off-season during the Southern Ocean winter when no other fishing boats are in the Ross Sea. And while the fish’s flesh will garner a hefty price when it’s landed in New Zealand, it’s not exactly the trophy the men onboard have come for. What they really want is to catch toothfish in the act of making other toothfish.

When the Janas’s crew drops their fishing lines, a scientist onboard—New Zealander Darren Stevens—also deploys a fine-meshed net shaped like a large windsock, hoping to scoop fertilized toothfish eggs from the water. The eggs are not profitable, but they contain a gold mine of information.


Researchers think toothfish breed on undersea mountains and ridges in the north Ross Sea sometime between May and September, but they don’t know for sure because nobody visits the sea during the treacherous, ice-choked Antarctic winter. No one has even seen the fish’s eggs or larvae, and the missing information leaves a hole in the knowledge used to determine fisheries policy. That’s why finding the eggs in situ, on the breeding grounds, is crucial. Without them, researchers piecing together the toothfish life cycle have had to estimate the egg size, the location and timing of their release, and other details.

The sketchiness worries conservation groups, such as the Last Ocean, which argue that scientists don’t know the fish well enough to set a sustainable quota. Scientists and governments want to solve the mystery, especially the 25 countries in the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which sets the catch limit for the Ross Sea. Russia, South Korea, Chile, the United States, China, and the other CCAMLR nations have given the Janas a special catch allowance to fund a risky winter journey.

pans of shifting sea ice in the Ross Sea, Antarctica

In the Antarctic winter, pans of shifting sea ice make navigation a constant challenge. Photo by Darren Stevens

To try to find the eggs, the Janas, with Stevens aboard, left New Zealand on May 22, 2016. On any other toothfish egg-hunting journey, Steve Parker, a Ross Sea fisheries expert at New Zealand’s National Institute of Water and Atmospheric Research, would have been lining up to get on the boat. But Parker had a meeting he couldn’t get out of so he asked Stevens, a colleague, to take his place. Stevens had just come from the United Arab Emirates, where the temperature topped 40 °C. Now he’s journeyed to a place that often gets down to -18 °C—so cold the Janas’s water pipes keep freezing and crew have to periodically thwack icicles off the railings with a shovel to stop the boat overbalancing.

Skipper Jeff Pitt thought they’d be able to catch their allowance within about two weeks and leave before the full onslaught of winter, but now, six weeks into the journey he’s had trouble reaching the fishing spots. He can’t risk getting the 46-meter-long vessel trapped in the thickening “pancakes” of ice since the nearest rescuers are several days away.

Satellite images give Pitt a crude idea of the whereabouts of the biggest ice floes; the rest is up to his eyesight. Even once he reaches a fishing ground, he can’t linger; CCAMLR has given him strict instructions to drop only a handful of lines in each location. They don’t want him skewing the catch data by catching too many fish in once place—after all, this is no ordinary fishing trip and nations are waiting eagerly to learn what the toothfish get up to in winter. Pitt does what he can within the six hours of daylight, but each night the wind blows the sea ice around, presenting him with a fresh maze each dawn.

The effort seems excessive to learn about a fish’s breeding habits, but this is an exceptional species. Antarctic toothfish are at the center of the Ross Sea food web, and their chunky bodies supply sustenance to Weddell seals, killer whales, and sperm whales. It’s unclear exactly how many end up in the tummies of warm-blooded species, but the fish’s sheer size and abundance suggests it must be important to the ecosystem. The fish are found everywhere around Antarctica and they fill a role similar to the one sharks play in warmer oceans farther north, explains Parker. “As far as shaping the system, they are the only big fish down there that acts as a predator.”

Scientists used to think toothfish were dull, languid creatures, but that was largely based on seeing the fish hooked on a line. Then Parker obtained the first video of an Antarctic toothfish in its natural habitat. He saw a graceful, nimble predator that could make tight U-turns to snag its prey. The fish mostly eat squid and smaller fish species, but according to Parker, adults won’t turn down a dinner of younger toothfish or even something odder. “Nobody knows why, but they eat a lot of rocks,” says Parker. “The rule of thumb with toothfish is, if it moves, eat it. If it doesn’t move, nudge it and then eat it.”

The Antarctic toothfish may be eating rocks and anything that moves, but the world wants to eat the Antarctic toothfish. Every year, vessels from New Zealand, Norway, Chile, Russia, Spain, South Korea, the United States, and elsewhere compete for a share of the Ross Sea quota, risking conditions that, even in summer, can sink boats less-equipped than the Janas.

In less than two decades these fishing nations have shrunk the stock to less than three-quarters of its unfished level—though CCAMLR says the catch is still far too conservative to threaten the species.

Toothfish are prey for seals, whales, and other large predators in the Antarctic. Video courtesy of the NIWA

The area was left unfished until the late 1990s and now groups such as the Last Ocean want to leave the Ross Sea as a largely untouched ocean. These conservation groups would prefer to let whales, seals, krill, and fish interact without the influence of fishing boats, giving these creatures at least one place in the world that is free from human exploitation. Fishing companies, though, say banning fishing isn’t realistic and that CCAMLR is running a cautious, well-managed fishery. Without the vigilance of legal fishers, they say, pirates might move in.

Decisions over fishing quotas or outright protection would be easier if they were based on complete information, which has led the Janas and its human complement to the Ross Sea in winter.


By the end of June the crew has caught less than half its allowance, so Pitt extends the journey.

The crew is bored. They’ve watched all the DVDs, and have run out of fresh vegetables and cigarettes. Still, the toothfish are showing signs they might be getting close to breeding. Below the Janas, the vibe is reminiscent of an awkward school dance before the sexes start mingling. Some days the crew will haul in a line with only male fish, while other lines contain only females. The males are running ripe with milt, but the females’ eggs aren’t ready.

Pitt gives them three more days. After that, he will have tried fishing at all the ice-free seamounts and regardless of the catch they’ll return to New Zealand.

As it turns out, the delay helps science. Just as the crew is preparing to leave the area, the female fish start breeding. The large toothfish the two fishermen skewer turns out to be a female with ripe ovaries. They catch another spawning female the same day, and, by the next day, the Janas is catching dozens of females with ovaries primed to release mature eggs.

In the biting-cold factory room, each fish has its throat slashed before being bled and hauled to a stainless-steel workbench to be meticulously gutted then hung by its tail, joining the row of headless torsos ready for snap freezing.

An Antarctic toothfish haul in the hold of the fishing vessel, Janas

An Antarctic toothfish haul in the hold of the fishing vessel Janas. Photo by Darren Stevens

Then Stevens gets extremely lucky. In the nick of time, his mesh net scoops 17 translucent, fertilized eggs from the water, each one the size of a human fingernail. He places three in a clear beaker with a constant flow of salt water running through it, hoping they will mature. The eggs sink to the bottom, dead, perhaps bumped too hard as they were hauled in. Stevens knows other scientists back at home will want to study the precious fertilized eggs and doesn’t want to waste any more, so he launches into a backup plan: artificially fertilizing eggs from fish caught by the Janas’s crew. He mixes milt from males and eggs from females hooked by the fishermen in sterilized plastic containers and places the ones that successfully fertilize in his makeshift incubation beaker.

The three days are up and Pitt says it’s time to leave the Antarctic. As the Janas’s crew prepares to depart for New Zealand, Stevens is below deck, nurturing his developing embryos. Every day he tests them in a buoyancy chamber to see how deep they float, which tells him where they would sit in the ocean and will help scientists extrapolate how far the eggs could be carried by currents before they hatch and the fish are old enough to swim.

Soon the Janas hits rough seas, but Stevens manages to keep the nascent toothfish alive for a few more days before the turbulence sloshes his precious embryos too much and kills them.

Instead of being downcast, Stevens is elated. He now knows when the fish start breeding (mid-July), where they do it (on the northern seamounts of the Ross Sea), and where ocean currents might carry the young during their first days of life. It’s all vital data that will improve the toothfish population models and much more information than he had just a few days earlier. He can’t believe how close he came to missing out on finding eggs. “We were lucky,” Stevens says, “it wasn’t until the last two days that we caught most of the spawning fish.”


The Ross Sea and the Antarctic toothfish swimming in it face an uncertain future. In October 2016, CCAMLR nations finally ended years of wrangling over a proposed marine reserve put forward by New Zealand and the United States. The countries unanimously agreed to safeguard much of the Ross Sea in a new marine protected area, the largest of its kind in the world. But the protections won’t affect the fishing quota. And the marine reserve will be up for renegotiation in 35 years.

Massive toothfish are nimble hunters that can deftly deke and maneuver in their pursuit of prey. Video courtesy of the NIWA

While Parker admires the toothfish, he is neither for nor against fishing. Politicians and diplomats can decide whether the boats can go; his role as a scientific adviser to CCAMLR, he says, is to supply good information.

This is where the results from his colleague Stevens will help. For example, Parker explains that the current fishing fleet tends to catch more males than females in the northern portion of the sea and more females close to the continent. CCAMLR needs to consider how to spread the catch limit around the sea to avoid skewing the toothfish sex ratio. Now that Parker knows the toothfish spawn in the northern, male-dominated region, it adds more complexity to the decision.

Bolstered by the expedition’s success, Parker wants to reveal more toothfish secrets. He and other researchers plan to ask CCAMLR if a boat can return to the Ross Sea in July 2019 to observe more of the spawning season. But before then, in July 2018, he and a team of researchers will set out from Scott Base in Antarctica and journey across the Ross Ice Shelf, where they will set up tents, drill holes in the ice, and drop fishing lines into the sea underneath.

Just as Stevens pioneered toothfish science by venturing to the edges of the sea ice in winter, Parker and his crew will probe for the fish in an even remoter part of their habitat, hoping to find another breeding ground hidden deep under the permanent ice shelf. There, during the coldest months, toothfish are usually safe from seals, whales, fishers—and curious scientists, eager to learn more about these remarkable, deep-dwelling predators.