Even by the standards of Hong Kong’s depleted waters, this has been a poor start to the day for trawlerman Wong Ah-Sheng and his wife Zheng Ah-Mei. It is 9.30am on a Tuesday in April and I have joined the couple for a two-hour trawl along the south side of Hong Kong Island. The meagre fruits of the trip lie on the afterdeck of their powerful, three-engined fishing boat: some very large and worthless jellyfish; an old cola can; a yoghurt pot; a few shrimps and crabs, and a pile of tiny fish, each measuring two and a half inches from nose to tail.

There is not much here that Zheng will be able to sell on the couple’s fish stall in the Ap Lei Chau market. Most of the meagre catch will be sold as feed for fish farms. Zheng estimates the total value of this haul is HK$200-300 (£13-£20). It isn’t even enough to pay for the diesel.