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Efforts Aimed At Better Understanding Of Juvenile Salmonids In Columbia River Estuary
Posted on Friday, November 03, 2017 (PST)

Some 114,050 acres of native fish and wildlife habitat in the lower Columbia River have been lost to development since the 1870s, according to Lower Columbia Estuary Project information.


LCEP has set an ambitious goal of recovering 60 percent of what it believes to be recoverable habitat and since 2000 has been working towards that goal. Its success could be a boon to migrating juvenile salmon and steelhead, offering them more areas to stop, rest, feed and, for subyearling chinook in the lower estuary, rear.


Catherine Corbett, a scientist with LCEP, described the organization’s activities and plans for restoring the river estuary at a Northwest Power and Conservation Council-sponsored Ocean and Plume Science conference last week, Thursday, October 26 in Portland.


LCEP is joined in its habitat restoration work with others -- NOAA Fisheries, Washington Department of Fish and Wildlife and Oregon department of Fish and Wildlife, and others – to better understand the survival of juvenile salmon and steelhead in the more than 100 miles of the lower Columbia River downstream of Bonneville Dam. The partners want to know where salmon eat, what they eat and even if they eat, whether the density of fish in the river may affect food availability and, ultimately, whether the fish survive, according to an October 31 blog by John Harrison of the Council (


In the 1870s there was 224,081 acres of available habitat along the river between Portland and the ocean, but that has declined by half due to development, agriculture and the flood control gates and dikes found in the lower estuary.


Some 77,210 acres of those lost acres can be recovered according to Corbett. LCEP’s goal, working with conservation groups and state and federal agencies, is to restore 22,000 acres, adding to the 23,195 acres already recovered and protected since 2000, Corbett said. That work has involved more than 200 projects, some of them completed and some currently in planning, design, or implementation. The sum of what’s been recovered – 23,195 acres – plus LCEP’s goal of 22,000 more acres sums up LCEP’s goal of recovering 60 percent of recoverable habitat.


Part of the effort to restore estuary habitat is to find out where the fish go and how much they eat and where, Harrison says.


“We are not finding that juvenile salmon in the lower Columbia are food-limited,” Corbett said. “Stomach contents consistently show active feeding. We are trying to determine whether some sites are better for fish than others.”


So far, it appears the area around Campbell Slough north of Portland at the Ridgefield National Wildlife Refuge is the best site for fish of the five sites that have been examined, she said. But that doesn’t mean it’s always the best site, as the river, fish, and prey are constantly in motion. Places that appear to have a good prey base for fish one day, or hour, or even minute might not the next, according to Harrison’s blog.


Meanwhile, NOAA Fisheries researchers, have examined the stomach contents of more than 1,000 juvenile salmon to better understand how the number of fish in the river, how much they eat, and where, affect growth and survival.


Corbett said that juveniles tested in the upper reaches of the estuary had emptier stomachs than those in the lower estuary. As an example of the feeding habits of juveniles, she said that 11 to 27 percent of fish tested in the John Day bypass facility were feeding, but feeding was even lower – 5 to 7 percent – in the Bonneville bypass. However, 56 to 68 percent of fish were feeding in the lower estuary.


Paul Wagner of NOAA Fisheries pointed out a 1984 study that generally saw full stomachs but noted that fish in the juvenile bypass system often lost their food, “so fish collected in the juvenile bypass may not be representative of all fish.”


“The Columbia is an incredibly dynamic environment,” NOAA salmon researcher Laurie Weitcamp said. “Hatchery fish had less food in their stomachs and were often found in higher densities, but I wouldn’t want to attribute low stomach contents to fish density if it was mainly due to year-to-year differences in fish productivity, for example.”


Ultimately, the researchers hope to better understand the effects of fish density in the estuary on competition for food, on fish survival and, as a result, the success of fish in the ocean as they grow and mature to spawning-age adults.


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