Thursday, 27 August 2009 08:30

Delta Bass Study

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Seaching for a real fish story: UCD grad student tracks the deltas largemouth bass

By Barry Eberling

McNaughton Newspapers


FAIRFIELD Anna Stephenson is catching largemouth bass in the Sacramento-San Joaquin Delta, cutting a short incision on their underside, placing a black tracking device inside their peritoneal cavity and releasing them back to the water.

Then she and other researchers will know when the eight or so fish with electronic devices leave shallow water for deep water. They'll know how the fish move about during the year.

And maybe they'll discover clues to the plunge in the numbers of native fish such as the delta smelt, which largemouth bass eat.

"I think it's really important to be studying all of these interactions, so we can manage the delta better, said Stephenson, who grew up in Chico and is a graduate student at UC Davis.

As a field ecologist, Stephenson is part of a research project searching for one more piece to the delta puzzle. It's a puzzle that involves more than fish, given that 23 million Californians get drinking water from the delta.

"I'm interested in how we can integrate the ecology of an area with the human needs, the human demand for water," Stephenson said.

When she leaves Stockton in a boat for the delta waters, the intense political battles in Sacramento over the areas fate are far away. She's in search of largemouth bass in a world of winding sloughs, levees, rivers and beautiful views.

"There was one day when a low-pressure system passed through, we had a little bit of rain, but the air was crystal-clear and Mount Diablo was in the distance," she said.

But she's had work to do on these beautiful August days. To put tracking devices the size of an AA battery inside of largemouth bass, she must first catch the fish. She uses a line with a plastic worm on it and lots of patience.

Largemouth bass were introduced by humans into the San Francisco estuary in the late 19th century and are a favorite catch of anglers. They are also predators of native fish.

Among the victims are delta smelt, a 3-inch-long fish that is having a profound effect on California's water world. Smelt numbers are crashing, the smelt are protected under the Endangered Species Act and one suspected cause of their drop is water exports. Judges have made a number of decisions limiting exports to help save the smelt.

Mention the delta smelt in Central Valley farming communities and the topic is likely to turn to how fish seem to be more important than people, given fallow land and the loss of jobs.

Researchers say water export pumping, salinity changes, pesticides and other pollutants and invasive species might all play a role in the smelt's decline. Stephenson is part of a project that will determine just how big a role, if any, the largemouth bass is playing.

"Not much work has been done on the largemouth bass," she said.

Should it turn out that the largemouth bass are playing a large role in the demise of native fish, the question will then be, what can be done? After all, the largemouth bass are present in great numbers in the delta and are a popular sporting fish as well.

"I don't know that weve gotten that far," Stephenson said. "I think our job as scientists is to provide data on the system and what's happening."

Still, she's interested in the other questions.

"We cannot just remove all the bass, because people love fishing for them," Stephenson said. "It makes the delta a really interesting system to work in, because there are all sorts of social and political issues as well as ecological ones."

For now, Stephenson has smaller concerns, such as what happens if an angler catches a fish with a tracking device. She's hoping the person would notice a yellow tag on the fish, toss it back in and give UCD and the researchers a call.

"Some of the fish might swim out of our study area," Stephenson said. "It would be great to know if someone caught it in Franks Track or someplace else."

That would be one more small piece to a massive puzzle.

-- Reach Barry Eberling at

This article has been reprinted in full, with permission from the Davis Enterprise newspaper.


If you fish in the Delta, please help these researchers collect data. Read this flyer regarding handling of tagged fish and reporting your catch.

Read 1296 times Last modified on Friday, 10 April 2015 13:46

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