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Feeding frenzy

Nourished by runoff, the Lake Mead food chain kicks into high gear.

September 06, 2005|Bill Becher | Special to The Times

AT Lake Mead, nature has done what humans had tried but failed to accomplish years ago -- stimulate the food chain and rev up fishing with a record spawn of baitfish.

Snowmelt and runoff from winter storms flushed tons of nutrients into the Virgin and Muddy rivers, which empty into the nation's biggest reservoir 30 miles east of Las Vegas. They carried a torrent of minerals that produced a plankton bloom that led to a surge of threadfin shad, the main forage for many game fish.

There's "a solid ball of shad so deep," according to Byron Velvick of Boulder City, Nev., a professional bass angler and former star of the TV reality show "The Bachelor," that the sonar transducer can't read through it.

Nevada wildlife officials confirm shad populations are well above normal levels.

In June, scientists found an average of 450 shad per cubic meter of water in the Overton Arm -- the huge dogleg that slices north from the main Colorado River channel near Arizona. That is nearly five times above the long-term average of 100 shad per cubic meter, says Nevada Department of Wildlife biologist Jim Heinrich. (A cubic meter is roughly the volume inside a refrigerator.)

"I'm sure the Virgin and Muddy rivers' inflows juiced the system and the shad are responding," Heinrich says.

Like Old West ghost towns, Lake Mead has had booms and busts.

Fishing surged after the construction of Hoover Dam as newly planted largemouth bass spawned and spread across virgin waters. But the days of catching huge bass did not last long.

When Glen Canyon Dam was completed upriver in 1963, biologists worried water levels would drop at Lake Mead during the spring when spawning fish and growers in California needed the water.

Although millions of boaters visit Lake Mead annually, it is not managed for water sports. "It's managed for the guy growing tomatoes in the Coachella Valley," says Jon Sjoberg, supervising fisheries biologist for the Nevada wildlife department.

Eventually, submerged plant material in the lake died, the food chain suffered and the fishery declined, in a predictable cycle of Western reservoirs, says Chris Horton, a biologist with the Bass Anglers Sportsman Society.

Soon largemouth bass populations plunged, and striped bass started to look emaciated. In the 1980s, anglers and scientists dumped 20,000 gallons of liquid fertilizer into the Overton Arm each year for three years to promote phytoplankton that shad feed on.

But it was like trying to cool the Pacific with an ice cube. Lake Mead is so big -- at full pool, it holds enough water to cover the state of New York with water one foot deep -- that researchers concluded the experiment didn't significantly help fish and the project was not economically feasible.

Then drought gripped the Southwest during the 1990s, causing a further drop in water levels and wiping out more miles of bass spawning habitat.

But scientists say the lake is heading for an upswing, thanks to heavy rain and snowfall last winter. More shad will result in bigger, healthier largemouth, striped bass, carp, catfish and other species. Smallmouth bass, which were probably introduced to the lake illegally by anglers, are also spreading. Recently, fly fishers have been targeting the abundant stripers in sheltered coves.

"The anglers' use of [Lake] Mead has been going down, but the anglers are catching more fish," Heinrich says. "The fishing is good in this reservoir and it should get better in the next two or three years."

But anglers will need to be patient. For now, so many shad swim in the water that officials say game fish show little interest in lures and instead prefer to gorge on a long-awaited baitfish feast.

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