They said it couldn't be done. They said you couldn't change Japanese attitudes to eating seafood. They laughed when we said we planned to change the way some of Japan's biggest corporations, retailers, wholesalers and restaurants buy their seafood. Last week, we proved the doubters wrong.

Following a committed campaign by Greenpeace in Japan, and because of growing consumer awareness and concern about seafood sustainability, last week Japan's biggest retailer, AEON, announced several important commitments as part of a new policy designed to massively improve the environmental performance of the business. First and foremost amongst those commitments is an agreement to eliminate the illegal trading, harvesting and fishing of seafood from its supply chains.

Seafood Ranking Guide Activity in Tokyo

Seafood Ranking Guide Activity in Tokyo

From face to face meetings, publishing comparative retailer rankings on seafood sustainability, delivering consumer voices to the company's decision-makers and much else besides, our patient but determined campaign in Japan has won out, bringing this huge corporation around to commit to delivering sustainable seafood and other important environmental standards.

Our campaign and AEON's new commitment comes in the context of rapidly changing views and attitudes to seafood sustainability in Japan. Seafood consumption in Japan remains extremely high, but slowly consumers are beginning to understand that if they want to ensure the fish they eat is available into the future, then action needs to be taken now, not just by individual consumers, but also by the many businesses that fish, farm and sell seafood. As the country's largest retailer, AEON's progressive new commitment will mark the company out as a leader on seafood sustainability in Japan.

Of course the hard work starts here. With AEON's commitments to sustainable seafood procurement in place, the company now needs to begin the process of laying down a structured and transparent timetable for making these changes to its supply chains so that its own consumers (and Greenpeace campaigners!) can see that it is really delivering change.

Our work in Japan is part of a wider international campaign to improve seafood sustainability and transform key global fisheries such as the tuna fishing industry. This work is to ensure that they are operated sustainably. In Japan, we have been encouraging major retailers and tuna industry to make commitments to phase out wasteful and destructive fishing methods – and with considerable success! Today, we have major retailers and brands already sourcing or committed to sourcing sustainable tuna in countries around the world including the US, Canada, Australia, New Zealand the UK and elsewhere in Europe.

The news from AEON last week is not the end of a process but the start of a very important one. The doubters said we had no chance of changing corporate behavior in Japan, that public interest and demand for sustainable seafood would not come. They were wrong. The challenge of creating a sustainable seafood industry in Japan is on!

Oliver Knowles is an Oceans Campaigner at Greenpeace International.