Skip to content

Scientists gather in Oakland to discuss impact of bay dredging on wildlife

on May 25, 2010

Oakland is a port city. That means commerce, trucks, trains and boats. It also means dredging. Because the channels and ports need to be deep for boats to be able to get in and out, 3 to 6 million cubic yards of sediment have to be dredged every year in the San Francisco Bay. But while dredging is necessary for trade, it also poses a risk for animals that live in the bay. How to deal with these hundreds of tons of dredged material has been a controversial issue for the government and environmentalists for decades.

That’s why a group of scientists met last week for a symposium at the State of California Building in downtown Oakland. Scientists working for organizations including the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers and the San Francisco Bay Regional Water Quality Control Board listened to research about the impact of dredging on wildlife in the bay, and discussed how to best minimize its effects.

A casual bunch, in slacks, short-sleeved button ups—some with fish or bird prints—the scientists showed Power Point presentations and flow charts of the field work they’ve been doing. Among the side effects of dredging discussed at the symposium were the influx of invasive species and the presence of toxins in the sediment.

But one of the most talked-about effects of dredging was how a smaller, siltier bay may be changing the migratory paths and feeding locations for some fish.

Around 40 percent of California’s water drains into the San Francisco Bay, flowing in from the Sierra Nevada Mountains. But today the bay is one third smaller than its original size. When mining began in the 1800s, sediment was poured into the rivers and settled in the bay. At that time, geologist Grove Karl Gilbert calculated that over eight times the amount of debris was dumped into the Sacramento and San Joaquin Rivers than was removed during the construction of the Panama Canal.

When dredging of the San Francisco Bay began in the 1900s, shallows and wetlands were filled in as dumping grounds for sediment. As time wore on, the negative affects of dredging and sediment dispersal became more apparent. Mounds of sediment were found underwater throughout the Bay—making boat navigation dangerous—and light layers of silt filled in much of the shallow bay flats where animals lived and fed.

At the conference, most scientists reported on works in progress, and weren’t able to give definitive answers about how dredging is affecting the bay’s fish. But they did note changes in species’ behavior over the past few years, and several studies preliminary results hint that certain types of fish may be avoiding the dredged areas, or that the silty water may be harming their ability to breed.

For example, the North American green sturgeon—which migrates down the Sacramento Delta, into the bay and out toward the Pacific Ocean—has shown a steady decline in population. “They’re kind of a funky looking creature,” said environmental analyst Kat Ridolfi, who works for the San Francisco Estuary Institute. Like something out of the prehistoric ages, this giant fish is covered in large bony plates and has exceptionally long and flexible “lips” to suck up food. It also has been listed as a threatened species under the federal Endangered Species Act since 2006. “They have a low reproductive rate because they live a long time,” said Ridolfi.

The sturgeons’ migratory movement is related to currents and water temperature; they feed near shore and travel in deep water. Ridolfi said that based on her research, these sturgeon spend little time around dredging sites. “But little is known [about] why,” she said. “There are indirect negative impacts of dredging that we know of, like the introduction of invasive species and propeller strikes.” She said that more studies are needed to get a clearer picture of how dredging is directly affecting the sturgeon; she recommended that more tracking data be done and synthesized.

Marine biologist Alex Hearn of UC Davis is working on tracking data but is focusing on Chinook salmon and steelhead smolts. Like the sturgeon, both of these types of fish are born in fresh water, migrate to the ocean, and return to spawn in the fresh water again. The group Hearn works with has tagged thousands of fish to study migration movement and survival. To tag the fish, the scientists do a small surgery: “We cut them up, stick in the tag and sew them up again,” said Hearn.  Once released, the tags are detected by dozens of listing stations throughout the delta and the bay.

The results show that the fish are migrating fairly quickly, taking two and a half days to get from Benicia to the Golden Gate. However, they are spending little time in dredged sites. Hearn cannot explain why they are avoiding the dredged sites, since his group is still in the initial phases of tracking these fish and trying to understand their migration patterns.

Another group of scientists found that dredge sediment could be affecting the survival rate of Pacific Herring. This fish is unique because the eggs that the females release are adhesive for the first two hours of their lives. “Adhesion is important because the egg adheres to anything,” said research biologist Fred Griffin, who works for the Bodega Marine Laboratory at UC Davis, “and anything can adhere to it.”

When Griffin’s group exposed these adhesive eggs to sediment they found that particles attached and stayed there permanently. When compared with a control group of eggs and larvae, they found that this sediment caused a reduction in larvae hatching, reduced the size of hatched larvae, and increased the number of abnormal larvae and larvae that hatched earlier than normal, which shows stress, Griffin explained. There was also a reduction in survival of the just-hatched fish.

Due to concerns about the welfare of wildlife, since the 1970s it has been tougher for developers and others to get permits and dispose of sediment. This is mostly due to the work of the Long-Term Management Strategy (LTMS) program for dredged material from the San Francisco Bay Area, which organized the recent dredging symposium. The organization’s goals are to reduce disposal within the bay, increase recycling of dredged material, review sediment quality and have a permitting process that takes into account the impact on the Bay’s wildlife. As environmental analyst Ridolfi put it during the symposium, “It’s important to take into account the economic needs of dredging along with managing the environmental needs of the bay.”

Find more information on LTMS, their studies and work here.

Want to get updates on the latest news from Oakland North? Join us on Facebook

1 Comment

  1. Catrina Kephart on July 21, 2011 at 2:21 am

    What some call health, if purchased by perpetual anxiety about diet, isn’t much better than tedious disease.

Oakland North welcomes comments from our readers, but we ask users to keep all discussion civil and on-topic. Comments post automatically without review from our staff, but we reserve the right to delete material that is libelous, a personal attack, or spam. We request that commenters consistently use the same login name. Comments from the same user posted under multiple aliases may be deleted. Oakland North assumes no liability for comments posted to the site and no endorsement is implied; commenters are solely responsible for their own content.

Photo by Basil D Soufi
Oakland North

Oakland North is an online news service produced by students at the UC Berkeley Graduate School of Journalism and covering Oakland, California. Our goals are to improve local coverage, innovate with digital media, and listen to you–about the issues that concern you and the reporting you’d like to see in your community. Please send news tips to:

Latest Posts

Scroll To Top