Scientists have just discovered that the models we’ve been using to predict abundance of orange roughy in a large area east of the South Island were flawed—and overly optimistic.
Orange roughy are one of our most important deepwater fisheries. The mistake means catch limits are geared around a much healthier population. Now, scientists are warning of “sustainability concerns”.
Orange roughy live in waters around a kilometre deep, and are slow-growing and long-lived. Maturing at 25 or 30, they usually live well into their hundreds and can reach more than 230 years old. New Zealand started fishing for them in the 1970s and 80s, and our vessels now account for 80 per cent of the global catch, netting $50 million in export earnings per year.
Since 2018, stock assessments have shown healthy and growing populations of orange roughy around the Chatham Rise, a huge undersea plateau that extends from near Akaroa past the Chatham Islands. Fisheries ministers have increased the quota accordingly—to nearly 8000 tonnes per year in 2021, more than double what it was in 2012. In 2022, the fishery was re-certified as sustainable by the Marine Stewardship Council (MSC).
But this year, when NIWA scientists took a look at the latest information, it told a different story. An important data source—an acoustic survey that uses sound waves to estimate the number of spawning fish—was delayed two years, and when it was completed in 2022 showed that the numbers of spawning orange roughy to the east and south of the Chatham Rise were in fact “flat or declining”. Fishing catch rates are down, too.
The NIWA team also identified “significant concerns” with the assumptions about orange roughy biology underlying the model.
“The old assessment said the stock should have been rebuilding quite fast,” says Richard O’Driscoll, NIWA’s chief fisheries scientist. “That wasn’t borne out by the observations that we’ve made since.”
The findings led the Deepwater Working Group—made up of fisheries scientists and bureaucrats plus industry and NGO representatives—to reject the 2020 stock assessment for the eastern and southern Chatham Rise area. Nor were the NIWA scientists able to complete a new one: more research is needed before they can confidently assess the health of the population.
That could lead to the fishery’s sustainability certification being revoked, says the MSC’s Matt Watson. “A fishery without a stock assessment probably has some challenges.” Independent auditors are reviewing the new information to determine whether to suspend the certification.
How did we get it so wrong?
In theory, fisheries management is meant to work like a bank account, O’Driscoll explains. A given population of breeding-age orange roughy is thought to naturally increase by 4.5 per cent per year, as young fish get old enough to spawn or be caught. Fishers should be able to haul up that 4.5 per cent (the ‘interest’) while leaving the rest of the population (the ‘deposit’) alone to breed.
Reality might be less predictable. Counting fish is famously like counting trees, he reminds me, “only they’re invisible and move around.” That 4.5 per cent could be optimistic—Australian fisheries scientists assume a lower ‘interest-rate’ for their orange roughy. Breeding success may also naturally fluctuate. “There might be lots of really bad years for orange roughy, followed by exceptionally good ones once every 20 or every 40 years—the fish are so old we don’t have enough of a time series,” O’Driscoll says.
The orange roughy coming of age now were born when fishing was just getting started—but “we’re not seeing the number of babies that we would have expected from a virgin population.” Individual fish may not breed every year, he says, or maybe the sample sizes are too small—scientists aren’t doing enough research tows to get a clear picture.
“We know more about orange roughy than many of our New Zealand fish species. But they are difficult to measure and to manage,” he says. That’s because of their age, the great depths they live at, and the fact that hundred-year-old fish aren’t dumb—they learn.
“When a new feature is fished, catch rates decline much faster than the population does. That’s probably the fish learning that when you hear a rumble of a boat overhead, you get out of the way.” In the western Chatham Rise, for instance, orange roughy like to spawn on Morgue—a seamount that has been closed to fishing since 2001.
Barry Weeber from the conservation group ECO worries that dragging trawl nets through groups of fish while they’re spawning may be putting them off their game. “We need a lot more information than New Zealand currently has about orange roughy.” By 2014, we were spending less than half on fisheries research in real terms than we did in the 1990s, he says, and it’s only gotten worse since then.
“It’s basically ‘fish and hope’—you hope that in 30 years’ time that the fishery is still there, and you haven’t had huge impact on it.”
Fisheries New Zealand is currently consulting on three options for the south and east Chatham Rise fishery from October—cuts of 15, 35, or 40 per cent to the existing total allowable catch. The new uncertainty means “the status quo is not an option,” the discussion paper says. (Submissions close at 5pm on Monday, 24 July.)
The 35 per cent cut would take the allowed catch back to 2018 levels, while 40 per cent is based on what the 2022 acoustic survey suggests about the size of the breeding population. That would be a start, says Weeber.
“You’ve got to be precautionary, and in the main, they haven’t been.”
O’Driscoll is worried too—about the implications for the fish, and for fishers’ livelihoods, if we get it wrong. “The indications are that we might not be in the place that’s best for everybody, and we should be trying to get to a better place—so the industry can catch more fish, and we’re not threatening the sustainability of the population.” But the government is responding to evolving science, and that’s what’s supposed to happen, he says.
“Have we got it exactly right? Probably not. But the stocks are relatively stable, they’re not plummeting towards zero. We’re still observing aggregations of thousands of tonnes of orange roughy on the Chatham Rise.”
“Significant work” is now needed before scientists can pull together an accurate stock assessment, officials say—including further surveys at sea and examining orange roughy ear-bones, called otoliths, to learn more about their age. The new information may also have implications for the health of other orange roughy fisheries around New Zealand, O’Driscoll says, so all future stock assessments will need to check whether the same problems are occurring in other places.