LAKE POWELL — Wayne Gustaveson had been working for years to convince people that what the game fish in Lake Powell needed most was more food on the table.

A single forage fish was simply not enough to feed all those mouths, he argued. But not everyone agreed. So the lake was left with the threadfin shad as its main source of food.

A few years back he got his new fish — albeit quite by accident. Gizzard shad were "accidentally" released into a lake that was linked to Lake Powell by the San Juan River.

Last fall, during a gill-net survey, aquatic technicians found an abundance of gizzard shad, the secondary forage fish Gustaveson had been asking for to feed striped bass, as well as largemouth and smallmouth bass, walleye and even crappie.

Each fall biologists canvas the entire 2,000-mile shoreline of this red-rock playground examining trends in fish size, health and population densities. Five years ago Gustaveson, Utah Division of Wildlife Resources fisheries project manager for Lake Powell, found what he called a mixed blessing in the San Juan arm.

"It was either July or August when we found the first gizzard shad in the upper stretch near the inflow above Copper Canyon into Mike's Canyon. That was in 2000," he said.

Two summers later biologists found them throughout the San Juan River arm of Lake Powell. By 2003 gizzard shad showed up in surveys throughout the lake from Good Hope Bay near Bullfrog Marina in the north to Waheap Bay near the Glen Canyon Dam.

"In 2004, we found good numbers of fish in our surveys. This year the gizzard shad population is taking up nearly 27 percent of the biomass," Gustaveson said as he examined some of the netted shad lined up along the back deck of the trawler used to establish camp and a miniature lab on the lake.

The netting results in 2005 along the San Juan arm were high. Of the 437 fish collected during the two-day sample, 177 were gizzard shad.

Gustaveson explained that the gizzard shad were introduced into the San Juan through Morgan Lake near Shiprock, N.M., when largemouth bass were stocked from a federal hatchery in Texas. The shad were mixed in with the game fish. When the lake spilled over into the San Juan River during spring runoff, the shad had their opening and slowly worked their way west into Lake Powell.

"We did not know they were in the river until we started checking and found them five years ago," Gustaveson said. "The gizzards had been established in Morgan for nearly four years before anyone started to look for them elsewhere. No one looked for them before that time. Navajo reservation biologists are in charge of the reservoir. It was so far from us we had no idea what was going on."