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SPECIAL BAY-DELTA SCIENCE CONFERENCE EDITION
Part One
October 2, 2018
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ESTUARY News sent reporters to the biennial Bay-Delta Science Conference in September. This special three-part edition of Pearls shares more than 20 takeaways. Today’s stories highlight presentations on native and invasive species.
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Recent restoration efforts in lower Putah Creek have had a big payoff: fall-run Chinook are once again coming there to spawn. Salmon bred in the watershed historically, but numbers were low before the restoration began, and non-native fish dominated. Now native fish have rebounded in the creek. “They outnumbered non-natives pretty rapidly,” says Eric Chapman of UC Davis. Putah Creek, which flows from Lake Berryessa to the Yolo Bypass, hasn’t supported a salmon run since the mid-1900s; in 2016, 1,800 adult salmon returned to spawn. Carcass surveys showed that the first adults to return had all been trucked to the Delta as smolts, rather than released directly from hatcheries. Now, salmon are laying eggs in Putah Creek, and some of the recent returners may have been born there. This makes the creek a model of “if you build it, they will come” salmon restoration. “Streams you may think are too far gone can be a success,” Chapman says. RM
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Southern-most populations of salmon are at the forefront of the effects of climate change, and they exhibit warm-adapted traits. Kenneth Zillig of UC Davis compared hatchery smolt from three populations that are adapted to different temperatures: one from northern Oregon, one from southern Oregon, and one from the Central Valley. Tests included raising smolt at a range of temperatures (11, 16 and 20⁰C); Central Valley salmon grew optimally at the highest temperature while the Oregon salmon did not. While this fits with southern-most populations being more adaptable to warmer waters, it’s too soon to say for sure because other findings were mixed. To get a more definitive answer, Zillig plans to expand the study to populations as far north as British Columbia or Alaska. “Larger biogeographical patterns may become apparent with future research,” he says. RM
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Although returns of spawning spring-run Chinook dropped precipitously to a low of 1,796 in 2017, there are signs that the fast dwindling species may be able to bounce back. Rachel Johnson of the National Oceanic and Atmospheric Administration has found evidence of hidden diversity that “highlights remnant behaviors occurring in multiple populations that are contributing to the resiliency of spring run.” For example, spring-run Chinook migrate to the ocean at a diversity of sizes and different times, increasing the chances that some will make it out to sea. They are also more spatially diverse than expected. “We thought they were extirpated in the San Joaquin River, so all the surveys there are for fall-run,” Johnson says. Recently, however, videos have caught spring-running Chinook in tributaries of this river. These chance sightings add up to a surprise: these salmon may be trying to recolonize the San Joaquin River naturally. RM
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Cordgrass is key to buffering vulnerable shores, but our native species could have trouble adapting to sea level rise. That’s what Erik Grijalva of UC Davis found when he transplanted cordgrass collected from the North Bay (where it is free of hybrids of the Atlantic species) to different depths at Sears Point and Eden landing. Only the shallowest sites had good survival rates, and there seemed to be limited variation among plants for natural selection to work on. These are very preliminary results, but Grijalva muses on a troubling thought: that the successful campaign to suppress the exotic cordgrass, which grows in a wider range of conditions, “might not have been exactly what the doctor ordered.” JH
Photo: Erik Grijalva
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Only a tiny percentage of outmigrating Chinook make it to sea, and where they begin their journey seems to affect their survival rates. “Where do fish die and survive on their way to the Golden Gate?” asks Colby Hause of UC Davis who is tracking young spring-run salmon to identify perilous reaches on their journey. When young salmon with acoustic tags are released in a restored stretch of the San Joaquin River, they did poorly immediately after release in the restoration area, better in the lower river, and poorly once again in the Delta. Altogether, only three to six percent survive their trip from the river restoration release site to the ocean. In comparison, prospects for young salmon released directly in the Delta look better: 10 to 19 percent survive their trip through the Delta and Bay out to the ocean. That said, a closer look at the data reveals that young salmon may benefit from undergoing the hazards of the restored stretch of the San Joaquin River: 30 percent of these make it through the Delta and into the Bay, compared with just 20 percent of those released into the Delta itself. “Maybe they benefit from going through the wringer of the restoration area,” Hause says. “Maybe they’re getting smarter and stronger before going though the gauntlet of the Delta.” RM
Photo: Dan Cox, USFWS
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Researchers are using acoustic cameras to learn where and when predatory fish pose the greatest threat to young salmon traversing the Delta. “There are very basic questions that we don’t have answers to, like numbers and locations of predatory fish,” says Christopher Loomis of Humboldt State University. He’s looking for answers with DIDSON acoustic cameras, which use sound to capture high-resolution video. Analysis of these videos yields fish dimensions (length and thickness) that can then be compared to those of known species in a data library, distinguishing predatory from non-predatory fish with 98 percent accuracy. By combining acoustic camera surveys of predatory fish with concurrent surveys of predation on tethered smolts, Loomis plans to map predatory fish in the Delta. “We hope to highlight where predation hotspots exist and what creates them,” he says. RM
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Native populations of Delta smelt, longfin smelt, and Sacramento splittail were hit hard by the last drought and had a hard time recovering. Louise Conrad, a program manager for Estuarine Science and Synthesis with the California Department of Water Resources, and co-authors analyzed populations of native fishes as well as introduced species including striped bass, shad, and Mississippi silverside before, during, and after the drought of 2012-’16 to assess both resistance and resilience. She discovered that while neither the smelt nor the splittail clearly bounced back after the winter of 2016-’17—which was certainly wet but may have been too warm for the fish—both striped bass and American shad had some success. Conrad also studied resilience following four previous major droughts going back to the 1970s and discovered that, when the conditions are right, natives can recover well, as they did after the droughts of 1976-’77, 1987, ’94, and 2007-’10. “In recent history, we’ve seen that they have the capacity for resilience, and that’s a good sign,” she said. “Drought is nothing new to California, but it isn’t the same estuary that these fish evolved in.” NS
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Invasive aquatic plants like water hyacinth doesn’t just choke up Delta waterways, impairing boat traffic and habitat; they can also have a measurable effect on water quality. Vanessa Tobias, a researcher with the U.S. Fish and Wildlife Service, found that floating patches of water hyacinth affect water temperature, dissolved oxygen, and turbidity—not just within the perimeter of the patch itself, but as much as 100 feet out. It’s too soon to determine quite what that means for fish, native plants, or other aquatic organisms in the Delta, Tobias said, and water quality seems to recover quickly after patch removal. Meanwhile, Judith Drexler of the United States Geological Survey has found that the submerged aquatic plants water primrose and Brazilian waterweed, both of which are weeds rampant throughout the Delta, negatively affect flow velocity, turbidity, and sedimentation processes. This can be bad news for marshes that depend on sediment to keep up with erosion and sea-level rise, as well as for fish species—such as Delta smelt—that need turbid water for habitat and cover. “This vegetation is really working as an ecosystem engineer in the Delta,” Drexler said. NS
Photo: Judy Drexler
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Using powerful sensors mounted on satellites, NASA researchers can keep tabs on environmental issues like air pollution, harmful algal blooms—and invasive aquatic weeds in the Delta. Led by senior research scientist David Bubenheim in collaboration with the U.S.Department of Agriculture and the California Division of Boating and Waterways (DBW), the team uses satellite data to assess the growth and distribution of floating invasive plants like water hyacinth. The project began about three years ago and continues to evolve, Bubenheim said, as NASA’s remote-sensing experts refine their use of current and historical data and seek out new data sources such as the European Space Agency’s Sentinel satellite, which collects more information more frequently than the United States’ Landsat sensors. “Where we are focused right now is to be able to give [DBW] a map that has finer details as to how much plant is in a particular spot, how much biomass is there, and what species it is.” said Bubenheim. NS
Photo: Toxic algal bloom. Courtesy CDFW.
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Scientists with the USDA are increasingly turning to biological controls to combat water hyacinth, an invasive aquatic plant that clogs waterways, harms habitat, and impairs water quality in the Delta. Biocontrols—non-native insects that evolved with the water hyacinth, and won’t eat beneficial plants or harm Delta fish—have been used in the Delta since the early 1980s, with limited success, said Patrick Moran, a research entomologist now leading the agency’s efforts. Only one insect, the leaf-chewing/crown-boring weevil Neochetina bruchi, has established itself throughout the Delta, and its impact on hyacinth profusion has been limited. But the USDA is undeterred, re-releasing the leaf-sucking planthopper Megamelus scutellaris and the moth Niphograpta albiguttalis this summer—and planning to try again with the weevil Neochetina eichhorniae very soon. The agency has also looked to treat the giant riparian grass arundo, which invades levees and wetlands, with a shoot-galling wasp and a shoot- and root-feeding armored scale, the latter of which has become established. “These weeds in the Delta have reached proportions that biocontrol really always should be considered,” Moran said. NS
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Look for Parts 2 and 3 of this special Science conference edition of Pearls featuring stories on habitat, restoration, climate, water quality and more later this week.
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Editor: Cariad Hayes Thronson
Contributors: John Hart, Robin Meadows, Nate Seltenrich
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