A scientist who crossed the world to study shark populations in New Zealand waters made a slow-burning, alarming discovery.
Over two summers in 2007 and 2008, New York-based biologist Demien Chapman carried out aerial surveys of an area around Banks Peninsula on the South Island's east coast which was known to be a hotspot for basking sharks.
In at least 20 hours of flying, his team did not spot a single specimen.
"We were puzzled," said team member Clinton Duffy, from the Department of Conservation.
"In the early 90s, aerial surveys ... routinely recorded sightings, sometimes with schools of 50 to 100. But we didn't see any in two years, which was quite unusual."
Basking sharks, which are now protected by law, were believed to be killed by set nets and long-line tuna and hoki fisheries.
Some of them had their fins sliced off by New Zealand and foreign trawlers while their carcasses were disposed of. The fins were exported to Asia for use in a mostly tasteless, but popular broth.
This controversial finning practice is under increasing scrutiny in New Zealand, with more than 100 countries including the United States and the United Kingdom moving to, or considering, a "fins-naturally-attached" policy.
In the next few months, the Ministry for Primary Industries will release a National Plan of Action for the protection of sharks in New Zealand waters.
Conservationists say our lack of protection measures - sharks could be finned alive until four years ago - is a source of global embarrassment.
The fishing industry, and some marine experts, argue that the finning debate has been clouded by emotion and a policy change would not only be costly but also prohibitively complex.
In November, concern about shark finning led MPs from both sides of the House to make a rare show of political unity on Parliament's steps.
Labour, Greens, New Zealand First, Mana, the Maori Party, United Future and Act all signed a petition to end finning. National was the only party not to sign up.
The New Zealand Shark Alliance, which organised the petition, said that the cross-party support meant a policy change should be a certainty.
Rules around shark fishing are reviewed every four to five years because of the need to protect top-end predators, which help keep the marine ecosystem in balance.
National Institute of Water and Atmospheric Research (Niwa) marine scientist Malcolm Francis said sharks at the top of the food chain such as great whites and makos had small population sizes and were much more vulnerable to overfishing.
"They're like the lions and tigers. If you have too many, they eat out all the wildebeest and prey and their own populations would collapse. The lower levels of the food chain are much more abundant than the top levels.
"The other thing about sharks is a lot of species have a very low reproductive rate and a low growth rate. They've evolved to be able to handle the levels of natural mortality they receive, but they're not very good at adapting to an additional fishing mortality. You've got to be very careful to get that balance right."
Measuring shark mortality rates and the influence of the shark-fin trade was notoriously complex.
Pelagic (deep-water) sharks had huge migration circles and were difficult to track, and most of their culled fins ended up in China, which had unreliable customs records.
"Nobody really knows how many sharks are killed for their fins," says fisheries scientist Shelley Clarke, one of the few experts on the global fin trade.
The American researcher, who has a temporary post at Niwa, said there were pros and cons to the finning debate.
"Anything that gets people to be concerned about shark conservation is a good thing, but what we specialists really need to do is look beyond finning and focus on how many sharks are being killed, not how they are killed."
Her research had found that finning bans overseas had not stemmed decline in shark populations because they were poorly enforced, and there was a growing market for shark meat. But despite this, she supported a "fins-naturally-attached" policy in New Zealand because it was more feasible than trying to regulate bycatch.
Stakeholders met with the ministry to make their cases for shark protection last week.
Forest and Bird marine advocate Katrina Subedar told officials that many sharks were caught alive and a ban would give fisheries an incentive to release them back into the wild. Her organisation also wanted far greater research on shark stocks which would help inform catch limits.
The Seafood Industry Council told the ministry that if finning was banned, trawlers would be forced to store the entire shark body, which was worth less than tuna and decayed quickly, spoiling other fish in the hold.
Spokesman Don Carson said sharks were rarely landed alive, and a ban would prompt fisheries to throw away the whole body, which was more wasteful than the status quo.
Mr Carson: "We are concerned that live finning and finning of dead sharks is equated. It is not the same. One is illegal, the other is perfectly legal. One is cruel, the other is not, and that is a vital distinction that sometimes gets fudged."
Dr Francis said it was a little-known fact in New Zealand that if a fishing vessel finned a shark and threw the rest away, the weight of the entire shark was recorded in the boat's quota.
"Whether the fisherman lands the whole shark or just the fins, or just the fillets, or the head, or the liver, that weight is always scaled up to the whole weight. Ten fins is counted as ten whole sharks."
But this rule was not a panacea to overfishing. Shark quotas were based on limited information, and some slow-growing, deep-water sharks were not covered by the quota management system.
The ministry treats finning as an animal welfare issue, not a sustainability issue. Deputy director Scott Gallacher said there was no evidence that finning in New Zealand waters had led to fewer sharks. The ministry was, however, concerned about overfishing of migratory sharks that ranged across oceans.
A policy change would shake up the fishing industry, which would have to work out how to stop catching sharks which it was not targeting in the first place.
Dr Francis proposed two initiatives for government and industry.
He said officials should find out more about the habitat and depth range of deep-water sharks, so fishing boats could avoid catching them.
And fisheries should introduce "bycatch mitigation devices", or trawl nets which have separating panels which can capture fish at lower depths while releasing sharks caught at higher depths. Trawlers which operated in sea-lion hotspots already used this technology.
Even if scientists did not demand it, New Zealand was likely to be pressured to change its finning rules as the practice falls out of favour globally.
The soaring popularity of shark-fin soup has died down, with the Chinese government last year deciding to ban the dish from official banquets.
Ms Subedar said New Zealand was increasingly an international outlier in the finning debate.
This could be informed by the perception of sharks as ruthless hunters - New Zealand has had more unprovoked shark attacks since 1850 than in all of Europe.
Ms Subedar: "I think sharks are feared or loved. People fear them because they don't understand them or have watched Jaws one too many times.
"But on the other hand, people get really excited about these magnificent, ancient creatures that have been around since the dinosaurs."By Isaac Davison @Isaac_Davison Email Isaac