Bioenergetics modeling tests done as part of 2007-2010 research indicates that the presence of non-native American shad in the Columbia-Snake river could provide fuel for young fall chinook salmon as they motor each year toward the Pacific Ocean.
Young shad, a member of the herring family, also compete with native salmon for foodstuffs, according to a package of five research summaries forwarded to the Bonneville Power Administration last month. Bonneville funded the four-year investigation into the potential impacts that shad might have on native salmon and steelhead stocks.
The federal power marketing agency funds fish and wildlife projects as mitigation for impacts of the federal Columbia-Snake river power system on native stocks
The summaries, “Impact of American Shad in the Columbia River: Final Report,” were developed by U.S. Geological Survey researchers based at the Western Fisheries Research Center, Columbia River Research Laboratory in Cook, Wash. They were edited by biologists Michael J. Parsley, Sally T. Sauter and Lisa A. Wetzel.
The report can be found at:
The overarching objectives of the research projects were to collect data on the diet of juvenile and adult American shad, develop a bioenergetics model for American shad to provide decision support, and compile existing data on American shad and fall chinook salmon to populate bioenergetics models that can be used to test various hypotheses about interactions between salmonids and American shad.
Another objective was to conduct empirical investigations to gain insight into several areas of study where American shad may have impact in the Columbia River.
Bioenergetics modeling can be used as a tool to investigate the impact of non-native age-0 American shad on reservoir and estuary food webs.
“Although the spawning migration of American shad overlaps spatially and temporally with that of spring Chinook salmon, the most consequential ecological impacts of American shad may be linked to the large number of young produced each year in lower Columbia River impoundments and the estuary,” according to the report.
American shad, an East Coast native, were introduced to the West Coast in 1871 and had gained a foothold in the Columbia by 1885. But they did not blossom until the mainstem hydro system, starting with the completion of Bonneville Dam in 1938, “created favorable environmental conditions for upriver migration and spawning of adult American shad, as well as optimal growth and survival conditions for larval and juvenile stages (Petersen et al. 2003),” according to the report.
“From 1938-1957 an average of 16,700 adults passed Bonneville Dam each year (Quinn and Adams 1996). In the past decade, on average over 3 million adults pass Bonneville Dam annually and more than 5.4 million adults passed Bonneville Dam in 2004.
“However, the counts of adult American shad at Bonneville Dam began a precipitous decline in 2004 that continued through the conclusion of this study,” the report says.
“Today, American shad are a highly successful introduced species in the Columbia River basin, with some adults migrating upstream as far as Rock Island Dam on the Columbia River and upstream of Lower Granite Dam on the Snake River.”
“Several conditions exist suggest important species interactions are occurring between age-0 fall Chinook salmon and American shad. Large numbers of American shad hatch and rear in lower mainstem reservoirs of the Columbia River overlapping temporally and spatially with age-0 fall chinook salmon. Diet studies on age-0 fall chinook confirm that they feed on age-0 American shad,” the report says.
Subyearling “fall chinook are eating shad and they are eating a lot of them,” Sauter said of the modeling from what was admittedly “limited data” collected in 1996. Diet data collected from 13 fall chinook juveniles traveling down through the John Day Dam reservoir had had an average diet composition of more than 75 percent shad, which Sauter said an energetic value double that off another juvenile chinook mainstay, zooplankton.
“It’s a pretty rich food source,” she said. “The big question (for that part of the study) is, are they eating them?”
The researchers also used existing fall chinook data to model how varying levels of intake – 15, 50 and 80 percent of their diet at a relatively high feeding rate of 60 percent -- affected their growth rate. A 100 percent feeding rate would be the fishes’ maximum consumption rate.
The growth of juvenile fall chinook salmon was modeled using data from fall chinook salmon sampled at the McNary Dam juvenile fish facility in early July 2008-2009 and that modeling indicated that during the first half of July the fall chinook showed considerable growth, and the more shad they ate the more they grew.
Sauter said that the 13 fish sampled appeared to chose “the largest fish they could energetically handle.” Young chinook of about 100 millimeters (4 inches) in length were gulping down shad up to about 40 millimeters (1.6 inches).
That strong growth came to a halt and headed in the wrong direction in mid-July with the chinook actually losing weight for the last half of the month, according to the modeling.
The culprit? Water temperatures that rose to 20 degrees C (68 F) and higher.
“After mid-July it didn’t matter how much they ate, they couldn’t compensate for the high water temperatures,” Sauter said.
On the flip side, “juvenile American shad may compete with juvenile fall chinook salmon and other small native fishes for prey. The large numbers of American shad present in the river may alter or deplete zooplankton populations that sustain rearing salmon while contributing to the growth and population size of large predatory fishes that feed on juvenile salmon. Other fishes, such as the native prickly sculpin, may benefit from abundant and energy-rich American shad prey as well.
The five research summaries are:
-- “Diet of Juvenile and Adult American Shad in the Columbia River”
-- “Growth Characteristics and Otolith Analysis on Age-0 American Shad”
-- “Development of a Bioenergetics Model for age-0 American Shad”
-- “Thiaminase Activity and Life History Investigations in American Shad in the Columbia River”
-- “Verification of a ‘freshwater-type’ life history variant of juvenile American shad in the Columbia River”
The latter study “verifies the existence of a freshwater” type life history variant of juvenile American shad in the Columbia River by examination of length frequencies and otolith analysis.”
“…Columbia River American shad are anadromous and have been assumed to solely exhibit an ‘ocean-type’ life history, characterized by a short period of juvenile rearing in freshwater, followed by seaward migration and saltwater entry before age-1, with sexually mature individuals returning to freshwater to spawn beginning at age-3.
“Our results show that some juvenile American shad remain in freshwater for 1-2 years. Even if this life history variant is relatively rare within the American shad population, the sheer abundance of American shad produced in the Columbia River basin could result in appreciable numbers, potentially with significant ecological impact. We also show that migratory patterns among Columbia River juvenile and adult American shad are variable and more complicated than previously thought.”