SALMON could become extinct on Hampshire's two main rivers if a new dock development goes ahead, a leading fishery consultant has warned.

Dr David Solomon, who has been working on salmon and other fisheries for 30 years, told the public inquiry into plans for a container terminal at Dibden Bay that salmon were already under threat.

They were already "teetering on the verge of total collapse," he said and he added: "Any increased mortality at any stage of the life cycle would reduce stocks still further and is likely to contribute to the extinction of the stocks."

Salmon would have to pass through Southampton Water at least twice before they could reproduce, he said, warning that their journey through the estuary represented "critical and high risk".

"Typically, only ten per cent of the young fish that migrate to the sea return to the rivers as adults and much of this high level of mortality is believed to take place in the estuary and coastal waters," he said. The inquiry heard that the agency's concerns included the sediment caused by dredging and the main construction work, which would have the effect of narrowing the channel through which the salmon pass.

Mr Solomon added that one of the perils faced by returning salmon was "a significant level" of illegal fishing.

Some of it, he said, was done by people fishing for other species while other people went out deliberately to fish for salmon.

"One of the hot spots is the Redbridge Causeway and having surveillance there would greatly help with policing," he said.

Mr Solomon also told the inquiry that only one or two per cent of the salmon which did return to the Test from the sea survived to spawn a second time.

The Environment Agency has demanded a detailed set of monitoring and conservation measures from Associated British Ports, the Southampton Docks operator.

ABP counsel Martin Kingston took issue with some of those demands and on a clause requiring that the salmon populations should not be allowed to slip below 400 on the Test and 180 on the Itchen, he pointed out they had on previous occasions. In cross-examining agency scientist David Lowthion, he suggested: "The agency is, in effect, moving the whole responsibility for the maintenance of salmon stocks from it to ABP."

Mr Lowthion, head of the agency's southern region science and marine section, said he had insufficient information to disagree.