Government Flying Services helicopters have been enlisted in the escalating battle against gangs of mainland intruders who have poached fish and crabs from the Mai Po nature reserve and paddled off from their captors on their home-made 'mud boards'. Helicopters with police officers on board generated enough down-draught to stop the mainland thieves skating off across the marsh, said Superintendent Johnny Wong Mong-tong, the Lok Ma Chau divisional commander. 'When the mainlanders are blown off their mud boards, the helicopters are lowered to about one to two metres above the wetland and our officers then leap out and catch them,' he said. 'The mainland illegal immigrants are then handcuffed and lifted on to the helicopters before being taken to the shore.' Eight mainlanders - six men and two women - were caught in two separate operations on May 29 and June 25 after police sought help from the Government Flying Services. The mud boards are made of a two-metre-long piece of wood with a handle. The user stands or kneels on the board with one leg and uses the other to propel himself. Mr Wong said that in the past, up to 20 mainlanders at a time could be seen sneaking out at the Mai Po reserve about 2km from the boundary on the Hong Kong side once the tide went out. 'At first, they planted bamboo baskets on the marshes to trap mudskippers [fish] and crabs and returned two or three hours later. Each could catch 10 to 20 catty of fish and crabs a day,' he said. 'When our officers approached them, they jumped on their home-made mud boards and skid over the marsh to escape. They then skid to the Sham Chun river [which separates Hong Kong and Shenzhen] where they get on board their motorised sampans.' He said that previously, officers had got stuck in the mud when they ran into the marshes in an attempt to catch the poachers. It is understood that each poacher can make more than $1,000 a month by selling mudskippers caught at the Mai Po reserve. Mr Wong said poaching had been disturbing migratory birds stopping over at Mai Po and could not be allowed. Yesterday, officers mounted their third such helicopter operation, but only discovered a group of mainlanders catching fish on the mainland side.