double-crested cormorants that have been nesting in greater numbers each spring
and summer at the lower Columbia River estuary’s East Sand Island showed that
they could be pushed by human dissuasion from one spot to another, but only a
small fraction left the area altogether, according to preliminary results
produced during 2013 monitoring.
research data comes from one of several ongoing studies guided by, and funded
through, the U.S. Army Corps of Engineers to determine the effect estuary and
inland bird populations are having on Columbia and Snake River salmon and
steelhead stocks, many of which include naturally produced fish that are
protected under the Endangered Species Act.
analysis of data collected in 2013 in a variety of avian predation studies was
presented during the Corps’ Anadromous Fish Evaluation Program Annual Review
held in early December in Walla Walla, Wash.
avian predation studies also aim to evaluate potential strategies for reducing
impacts on juvenile salmon swimming down through from the
Columbia-Snake-Willamette river basin. The Corps is amidst the process of
completing an environmental impact statement regarding potential options for
reducing East Sand-based cormorant predation.
2010 and 2011 respectively, the colony consumed approximately 19.2 million and
20.5 million hatchery and ESA-listed juvenile salmonids per year, as the fish
migrated toward the Pacific Ocean, according to the Corps.
is the single most significant source of mortality affecting juvenile salmonids
in the estuary, researchers say.
estimate that losses of smolts to predation by Caspian terns and double-crested
cormorants nesting on East Sand Island in the Columbia River estuary were about
24 million fish in those years.
represents about 15-20 percent of all smolts that survived to the estuary.
cormorant colony size has grown each over the 1990s and 2000s at East Sand to
become the largest on the West Coast and likely in the world.
2012, as in 2011, smolt consumption by cormorants nesting on East Sand Island
exceeded smolt consumption by Caspian terns nesting on East Sand Island by a
factor of about 4, according to a team made up of Oregon State University-based
researchers as well as NOAA Fisheries scientists. The team is led by Dan Roby
of the U.S. Geological Survey-Oregon Cooperative Fish and Wildlife Research
Unit at OSU and Ken Collis of Real Time Research.
tern management plan is already well under way, with nesting habitat reduced to
1.58 acres, a 68 percent reduction from the East Sand colony area that existed
attempt is to persuade terns to relocate away from the estuary’s salmon
freeway. The Corps has since 2008 guided the construction of nine islands, six
in interior Oregon and three in the upper Klamath River basin region of
northern California, as alternative nesting sites. The Corps, and Bureau of
Reclamation, operate dams in the Federal Columbia River Power System. The
is also responsible for maintaining a Columbia River navigation channel that
allows upstream passage of cargo chips. Dredged materials from channel
maintenance has in the past been relocated in-river and has resulted in the
creation or expansion of islands such as East Sand.
of those sites were available in 2013 and five were used by terns, according to
preliminary results presented at the AFEP gathering by OSU’s Yasuko Suzuki on
Caspian tern management in the Columbia River estuary.
at the inland islands was relatively low due to a variety of factors, according
to the abstract for Suzuki’s presentation. Limits included mammalian and avian
predation on the tern nests and drought and other adverse weather conditions.
substantial number of Caspian terns from the colony on East Sand Island in the
Columbia River estuary, however, did use the alternative nesting sites created
by the Corp; 57 terns originally banded in the Columbia River estuary were seen
at the alternative sites in interior Oregon and 110 were seen at the
alternative sites in the Upper Klamath Basin during the 2013 nesting season,”
according to the preliminary analysis described in the abstract,
“Implementation of the Caspian Tern Management Plan: Status of Tern Colonies in
the Columbia River Estuary and at Corps-constructed Colony Sites.”
East Sand cormorant colony experienced a year of change in 2013, some human
caused and others not so easy to explain, according to “Ecological Developments
at the Double-Crested Cormorant Colony on East Sand Island: Status, Dispersal,
Management Pilot Studies, and Implications for Salmonid Restoration,” a review
of 2013 preliminary data presented at the AFEP conference by Roby.
double-crested cormorant colony on East Sand Island consisted of about 14,900
breeding pairs in 2013,” according to the study abstract prepared for the AFEP
review. Results presented at the conference are preliminary. Analysis of data
is for the most part fine-tuned over the winter and finalized ahead of the next
is the largest colony ever recorded on East Sand Island, and is about 15
percent larger than it was in 2011-2012. This one colony likely includes more
than 40 percent of the breeding population of double-crested cormorants in
western North America, and is the largest known breeding colony of the species
salmonids represented about 10 percent of the double-crested cormorant diet (by
biomass) in 2013, compared to 20 percent in 2012. Estimates of total smolt
consumption (based on bioenergetics calculations) and stock-specific predation
rates (based on PIT tag recoveries) by double-crested cormorants from the East
Sand Island colony are not yet available for 2013,” the abstract says.
commorant consumption of smolts in 2012 was about 18.9 million, and
population-specific predation rates for salmonid populations originating above
Bonneville Dam ranged from 0.6 percent to 7.2 percent of fish that survived to
the estuary, depending on the salmonid population.
past summer the Corps expanded on a pilot study that was initiated in 2011 to
test possible strategies for limiting the size of the cormorant colony. Fences
were built to bisect the colony, visually separating a 4-acre plot from the
other 75 percent of the former colony nesting area. Hazing was then employed to
prevent cormorants from nesting outside of the four-acre area. That effort was
successful, according to preliminary results.
sampling of cormorants were satellite tagged so that post-hazing movements
could be monitored. About 96 percent of the tagged birds dispersed from the
island, but 96 percent of them returned and attempted to nest.
some of the dispersed birds were later located at colonies and roost sites
elsewhere in the estuary, on the lower Columbia River below Bonneville Dam
(which is located at river mile 146) and up the Willamette River, on the outer
Washington coast including Willapa Bay and Grays Harbor, outer Vancouver Island
in British Columbia and in Puget Sound.
cormorants satellite-tagged on East Sand Island early in the 2013 nesting
season were detected along the coast of Oregon during the nesting season,”
according to the preliminary data.
AFEP studies evaluate passage success up and down the Columbia-Snake river
hydro system, survival, and fish condition for surface bypass technologies at
the dams, transportation of fish down through the system, conventional bypass
systems, spill as a passage alternative, the effect on fish of total dissolved
gas stirred up by hydro operations such as spill, adult migration/passage, in-river
passage and turbine passage. Most are developed as integral components of
larger studies and evaluation features of the Corps’ Columbia River Fish
Mitigation program related to new passage technologies, while others evaluate the
pros and cons of existing hydro project features.
research is largely funded by the Corps through congressional appropriations.
Those appropriations are repaid to the U.S. Treasury by the Bonneville Power
Administration, which markets power generated in the hydro system and is
obligated by federal law to mitigate for system impacts on fish and wildlife.
these drafts and preliminary research documents, opinions, interpretations,
conclusions, and recommendations are those of the author and are not
necessarily endorsed by the U.S. Army,” according to the Corps.