Though these chalk streams are famed for their clarity (the water is said to be as clear as gin and twice as expensive), you might still wonder how the passenger, a National Rivers Authority scientist, can hope to spot fish from several hundred feet in the air.
The answer is that he doesn't need to. Inside the salmon's stomachs are radio transmitters that enable the fish's movements to be traced as they head up river to spawn.
The NRA defends the use of helicopters, saying that they enable the whole river to be checked in an hour. But the wider issue may be whether the money being spent on salmon in the two rivers is really preserving a unique asset, or the mathematics of the madhouse. Since 1989, the NRA has ploughed pounds 843,000 into the Test and Itchen salmon to discover why they are in serious decline.
This season, 170 salmon-fishing licences were sold on the two rivers, an income of pounds 2,252.50. Much of the four-year spending ( pounds 340,000) has been gulped up by anti-poaching measures, though there have been a mere nine prosecutions. Fish passes accounted for a further pounds 250,000.
Maybe it would all be worthwhile if the result had been an abundance of salmon wending their way upriver. But despite nearly 770,000 baby fish going into the river in 1991 and 1992, just a handful have returned after the compulsory year at sea that all salmon must serve. The return rate on these Hampshire rivers is, mysteriously, the lowest in the British Isles.
Stocked fish carried microtags so they could be identifed, and it appears that about 25 per cent are falling to high-seas netting off Ireland, both legal and illegal. (Hardly any were caught off West Greenland and the Faeroes, which anglers have long blamed for stealing their salmon.)
Fishing is generally a pretty inefficient way of catching salmon. But on the Test and Itchen, scientists calculate that anglers are accounting for perhaps 30 per cent of the fish; it's not clear whether Hampshire anglers are better than their compatriots elsewhere, or whether the fish are just thicker.
More to the point is that the salmon may soon become extinct. There aren't enough coming back and those that do aren't spawning well enough to perpetuate the species.
All sorts of trials have taken place to clean sediment from the gravel beds that are vital for successful natural stocking. Baby salmon reared on fish farms to a size where they have a better chance of survival are supplementing wild stocks.
A catchment management plan has been produced. But the bottom line is that anglers, who expect to keep what they land because they have paid so much for it, may have to put back the salmon they catch. Once such a suggestion would have been unthinkable. Now it may be the fish's only hope of salvation.
Some powerful voices support this idea, including the renowned Mick Lunn, river-keeper on the elite Houghton Club stretch of the Test at Stockbridge. He said: 'I would like to have seen no salmon taken at all from the river this year.'
Lunn has played a big part in restocking but it is not the long-term answer. As David Jordan, NRA head of fisheries for England and Wales, said: 'I am not sure that stocking plays a significant role in the strategy . . . to tackle the causes of the problem.'
And as the NRA becomes more accountable, it is unlikely that helicopters will either.Reuse content