After winning against whale meat, now for the shark fin trade: Marine geneticist Stephen Palumbi

W I grew up in Baltimore, in the US. On my first dive, at the age of 10 - performed with a cheap mask, snorkel and air mattress, which I used to paddle offshore, at Ocean City - I plunged into a swirling school of spiny dogfish sharks and surfaced sputtering and alarmed, having mistaken the gentle animals for an aggressive species. But I was fearless enough to go back for a second glance. At about the same time, I began raising tropical fish at home. By high school, I had filled my family's living room and basement with a dozen tanks and was selling popular species to other aquarists.

As a marine biologist who studies sea urchins, cone snails and lace corals, public health wasn't my arena until EarthTrust and Greenpeace USA co-founder Don White approached me in 1994. He had a hunch that the legal sale of southern minke whale meat in Japan served as a cover for the illicit trade of endangered and potentially toxic species. I volunteered my expertise in molecular forensics to help pinpoint illegal whale species in food, by sequencing DNA in supermarket samples, which all looked like sirloin steaks and were simply labelled as - the generic Japanese term for whale. The problem was that it was illegal to fly samples, even of DNA, to our US-based lab if they proved to be from protected species. We decided to travel to Tokyo, enlist agents to shop for whale meat and turn a hotel room into a makeshift lab, where we extracted and prepared synthetic copies of the DNA to be shipped out lawfully.

Upon analysis, I was staggered to find less than half of the samples were what they were labelled as. The rest came from illegal-to-hunt species, such as humpbacks and fins, and some weren't even whales - the meat belonged to dolphins and porpoises. The magnitude of the deception was huge.

When we released the report, I expected Japan to scrutinise our allegations as rigorously as academics would, but they denounced us outright for having an agenda and operating on shoddy science. It was my first high-profile research after I had graduated and started teaching. Learning to deal with Japan's repudiation made me a better scientist. I realised I shouldn't shy away from upsetting people, but also learned not to make a conflict bigger than it has to be. I'm more than open to talk if someone challenges my methodology, but not if their problem is that they loathe the hard truth or its consequences. If there's a storm, I've taught my students to retreat to their evidence, which is irrefutable.

When I sent agents shopping for whale meat in Japan a few years later, the test results still returned showing a mélange of species, including dolphin and porpoise. But this time there was something much more sinister: the dolphin and porpoise products were laced with DDT, dioxin and mercury at levels as much as 500 times above World Health Organisation recommendations. It was so contaminated, no pregnant woman should touch it. Whale meat was considered safe to eat because the krill foragers live in the middle of the ocean, but dolphins don't since they are higher on the food chain; they live in more polluted, coastal waters. I remember sitting at my desk, thinking, "Oh my god, this is not only a crisis for ocean conservation but also public health." I wrote a letter to the Japanese Ministry of Health calling for public warnings and an immediate ban on sales of the contaminated products. It was the only time I circumvented the lengthy scientific publishing protocol, because I didn't feel right sitting on this information for a year or two, allowing citizens to be exposed to this danger unwittingly. At first Japan downplayed the findings, but eventually they passed food labelling laws.

Since then, DNA sequencing has become more affordable. For US$100, I can run 250 million sequences now, compared to just 19 sequences 20 years ago. The technological advances have helped me to unravel many mysteries. I discovered that the worldwide population of humpbacks before commercial whaling took off in the 1800s might have been 10 times more abundant than widely accepted. My findings caused uproar among the whaling industry, which counted on the (existing) figures to determine how whale populations were recovering and when hunting could resume. Previous estimates were best guesses based upon 19th-century whaling logs and the assumption we knew every whale every whaling vessel had taken. But that can't possibly be true. While the historians were very careful, researchers should always try to approach the same problem from other perspectives and see if it yields the same results. We blazed a trail by comparing the genetic diversity of past and present whale populations. We know that the larger the population, the more genetically diverse it is. That said, we should shift our focus from the past to the present. The value of whales underwater is higher than their value on your plate. The time for slaughtering whales is over. It's the era for celebrating whales through eco-tourism.