For years a small population of steelhead that overwintered in the Fraser River between Lillooet and Lytton has intrigued fisheries scientists. The fish arrive in the river in late October and early November, moving on a schedule similar to that of the famed Thompson River run, but then - in May - they vanish.

In recent years a few local sports anglers have discovered where the fish hold and have been able to catch them in the Fraser. But the run has been largely unknown except to a handful of fisheries biologists.

And even the scientists knew little about the fish. Where were they headed? Into nearby rivers, or up into the vastness of the Chilko River system, far upstream?

Genetic sampling of the fish failed to provide answers. But a few years ago, using electronic transmitters implanted in the fish, biologists from B.C. Hydro and the Ministry of Environment were able to unravel the mystery for the first time.

"Most of them appear to be going into the Bridge River," Hydro biologist Bryan Hebden said in an interview from his office in Kamloops.

Hydro, which has power projects on the Bridge and Seton Rivers, contributed $40,000 to the two year research project that got underway when 14 steelhead were caught in the Fraser and fitted with radio transmitters.

The fish held for the winter, but in early spring were on the move in, leaving their holding stations in the Fraser to seek out mates and find spawning beds.

One interesting female fish moved up into the Seton River for three weeks, but then suddenly pulled out, dropping back to the Fraser before heading up the Bridge River.

Mr. Hebden speculated that she may have been unable to find a mate in the Seton, so went searching up the Bridge, where the bulk of the run had gone

Fish were tracked out of the Fraser into spawning beds in the Bridge River.

Without the radio tags, biologists wouldn't have had this kind of information. The Bridge runs through deep canyons and is difficult to access for much of its length. Flying it in a helicopter, the usual method for evaluating steelhead spawning stocks, hasn't been productive because the fish are so hard to spot.

Using the radio tracking devices, fisheries workers found they could triangulate the signals, allowing them to hike down to the river and determine, within a few metres, where a fish was holding.

Even then, however, it's often difficult to find the steelhead, whose colors allow them to blend in so naturally with a river bottom.

"The water is crystal clear, but you can't see the fish," said Mr. Hebden.

"After about three hours (of waiting) the fish comes out of some rock cavity and you finally see it," he said, expressing a sense of wonder about how well the fish hide.

Because of the research, biologists were able for the first time to get some hard data on just when (May) and where steelhead spawn in the Bridge River.

"We are not talking about a big run of fish here," said Mr. Hebden. "It's probably less than 200 fish. It's certainly not paradise found. But all steelhead stocks are jewels and they deserver the proper attention."

A run of 200 steelhead seems miniscule compared to the runs of millions of pinks, sockeye and chum that typically go up the mainstem of the Fraser. But steelhead are the rarest and most remarkable of all the salmon species on the West Coast and are worthy of special management efforts.

The Bridge River stock is highly unusual too, in that it runs late in the summer. There are only a few runs of summer fish within comfortable driving distance of Vancouver, and if the Bridge stock can be protected and enhanced, it could some day prove to be highly valuable sports fishery.

Hebden said the fisheries study also gathered data on rainbow and bull trout, which, like the steelhead, are being fitted with colored, numerically coded tags.