Midges

Left: Hydrobaenus saetheri is a newly discovered species of tiny fly, or midge, now known to be a major food source for young salmon when water floods the Yolo Bypass.


Who knew that the mist of mashed midges made manifest on the windshield every day by driving, between Davis and Sacramento and back, across the Yolo Causeway, were SO IMPORTANT! We live in an amazing world!

Ted Sommer, a senior environmental scientist at the state Department of Water Resources, discovered about eight years ago that juvenile chinook salmon grow faster and fatter when the bypass floods. This vast flood corridor between Sacramento and Davis seemed to be an important feeding area for salmon – when floods allow them to swim into it.

"They grew like gangbusters, often twice as fast as fish that stayed out in the river," he said.

But nobody knew what the salmon were feasting on or where the food came from.

To answer that question, Sommer put an intern on the trail. Gina Benigno, then a recent UC Berkeley biology graduate, spent the winter of 2004-2005 taking samples in the bypass: water from ponds, water flowing into the bypass from creeks and drains, and the soil itself.

The dirt went into big plastic bins in a lab at UC Davis. She flooded the dirt with water and covered the bins with screens. And then she waited.

Within a few days, insect larvae hatched in the water and the bins were buzzing with adult flies.

Sommer and Benigno couldn't identify them, so they sat down with Peter Cranston, an entomology professor at UC Davis.

It took Cranston only minutes of squinting through a microscope to provide an answer. And it was he who came away most surprised.

Cranston is one of the world's leading experts on chironomids, a family of gnatlike, non-biting aquatic flies also known as midges. He travels the world hunting for new chironomids, but never expected to find one in his own backyard.

He and Benigno co-authored a paper last year identifying the bugs from the Yolo Bypass as a new species.

"It reflects quite badly on me," Cranston confessed. "At the time this was brought to my attention, I'd been here six years and been out to the Yolo Bypass bird-watching and never observed it."

Plenty of Sacramento commuters have observed the midges, usually as carcasses on their bumpers and windshields. The adult is only about 5 millimeters long, but when it hatches, it comes in clouds over Interstate 80's Yolo Causeway.

Such species are notoriously difficult to identify, said Norman Penny, an entomologist at the California Academy of Sciences. The Yolo Bypass midge ranks as a rare find because North America and Europe have been pretty well scoured by experts looking for bugs.

Scientists have identified and named a little more than 1 million animal species worldwide, he said, and at least that many more remain to be discovered. But most come from remote corners of the globe or from unusual places, such as caves and tree canopies.

"Who knows how many thousands of people have seen this fly before, but none had the background and the knowledge to recognize it as being different and new," said Penny.

The discovery may hold part of the solution to a decline in fall-run chinook salmon that is expected to be unprecedented this year. Regulators have closed salmon fishing to protect what remains of the salmon run.

Researchers now planning the future of the Sacramento-San Joaquin Delta are looking at ways to expand floodplain and tidal habitat to provide more feeding and resting areas for salmon and other fish. They're also considering adding flood bypasses to the San Joaquin River.

Approved in 1917, the Sacramento River bypass system is now seen as a visionary flood control project. When the river swells, the bulk of its flow spills into the bypass and is diverted safely around urban Sacramento. But its environmental benefits were unknown until recently.

"I think we know floodplains are really productive systems, and this was just a fun way of figuring out where a lot of that productivity came from," said Benigno, now a fulltime environmental scientist at Water Resources who is completing a master's degree in biology at Chico State. "It was really interesting that it just came out of the dried dirt."

Cranston named the new species Hydrobaenus saetheri, after Ole Saether, a retired entomologist colleague in Norway.

Cranston believes this midge lies dormant as a larva in the soil, perhaps inside a cocoon, during dry periods. When a flood comes, it emerges into the water and begins growing into an adult, when it is easy snacking for salmon.

Sommer and Benigno's research shows this midge makes up most of the flying fish food in the bypass during a flood. In a paper published earlier this year, they found the new critter accounts for 74 percent of the fly species in floodplain sediment, and 99 percent in the water.

Those that survive the feeding frenzy hatch into flying adults. These live only a few days but feed birds and bats in the bypass while they do. Those that fall dead on the water feed fish again, plus waterfowl and shorebirds.

The midge also feeds another native fish, the Sacramento splittail. Sommer documented that the splittail population explodes in years with at least three weeks of flooding in the bypass, and Hydrobaenus saetheri is why.

Such a clear relationship has not been established for salmon, but Sommer said it's likely.

"If there's not enough flow in the bypass to spill out onto the floodplain, the salmon don't do that well and their survival is poor," said Sommer.