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Lamprey wounds have been previously reported on 
several of the species we observed, including Pacific 
herring and juvenile Chinook salmon (Beamish and 
Neville, 1995; Orlov et al., 2009), and identifiable re- 
mains of American shad, Pacific herring, and juvenile 
salmon (tentatively identified as chum salmon [O. keta \ 
and steelhead) were described from stomachs of west- 
ern river lamprey (Bond et al., 1983). We provide the 
first report of lamprey wounds on shiner perch, surf 
smelt, and longfin smelt. However, we did not observe 
lamprey wounds on species that are common lamprey 
prey in the Strait of Georgia, including coho, yearling 
Chinook, and chum salmon (Beamish and Neville, 
1995), despite catching thousands of yearling Chinook 
and coho salmon and hundreds of chum salmon each 
spring (Weitkamp et al., 2012). Wound rates for com- 
monly wounded species reported from the Fraser River 
plume (10-21% of fish caught) (Beamish and Neville, 
1995) are much higher than the rates we observed 
(Table 2). It is not known whether differences in host 
species and wound rates between the Columbia and 
Fraser River estuaries are due to differences in physi- 
cal habitats, lamprey behavior or population sizes, fish 
assemblage composition, or other differences between 
the 2 estuarine systems. 
We suspect that the hosts we observed were vul- 
nerable to lamprey attacks because of both their size 
and habitat selection. Commonly wounded fishes were 
relatively large and had high temporal overlap with 
western river lamprey in the estuary. In contrast, small 
(<90 mm FL, 5 g) yet abundant juvenile surf smelt, 
chum salmon, and threespine stickleback ( Gasterosteus 
aculeatus ) were not observed with wounds, likely be- 
cause they were too small to serve as hosts for western 
river lamprey. The absence of wounds on most juvenile 
coho salmon, yearling Chinook salmon, and steelhead 
despite their relatively large size (>130 mm FL, 20 g) 
may be a result of rapid movement through the Co- 
lumbia River estuary (Welch et al., 2008; Harnish et 
al., 2012) that provided limited opportunity for pre- 
dation. Lack of lamprey wounds on larger American 
shad or extremely abundant northern anchovy (En- 
graulis mordax) may also reflect limited opportunity: 
large shad may have just re-entered freshwater and 
were moving rapidly upstream (Hammann, 1981), and 
northern anchovy are a marine species that typically 
enter the estuary only during high tides (Weitkamp et 
al., 2012). 
Murauskas et al. (2013) argued that the abundance 
of adult Pacific lamprey in the Columbia River is at 
least partially controlled by the abundance of their 
hosts during their parasitic phase in marine environ- 
ments. If this idea applies equally to western river 
lamprey in the Columbia River estuary, we expect that 
their population should be relatively healthy because 
of the abundance of potential prey in the estuary. In 
particular, it has been suggested that forage fishes in 
the estuary have greatly increased in abundance since 
the late 1970s as a result of alternations in river flow 
from main stem dams (Weitkamp et al., 2012). 
Furthermore, the population of nonindigenous 
American shad — the species most commonly observed 
with lamprey wounds — has numbered in the millions of 
fish in the Columbia River in recent years (Hasselman 
et al., 2012a). Although there are concerns about po- 
tentially negative ecological impacts to native species 
from abundant American shad in the Columbia River 
(Hasselman et al., 2012b), our data indicate that high 
American shad abundance may be beneficial to western 
river lamprey by providing a plentiful and ideal-size 
resident host. American shad may also shield native 
species from potentially lethal predation by western 
river lamprey. The recent catch of several western river 
lamprey and an American shad with lamprey wounds 
in the Yaquina River estuary (Cornwell 5 ) suggests that 
these benefits are not restricted to the Columbia River 
but may be occurring in other coastal estuaries where 
both species are present. Clearly, many aspects of lam- 
prey-host relationships are poorly understood and de- 
serve further investigation. 
Finally, our analysis of lampreys in the Columbia 
River estuary, although far from comprehensive, be- 
gins to fill a critical information gap about lampreys in 
estuaries in general and in the Columbia River estu- 
ary in particular (Mesa and Copeland, 2009). As with 
other lamprey studies (e.g., Hayes et al., 2013), we re- 
lied on data from research projects where — although 
lampreys were caught and recorded — lampreys were 
not specifically the focus of the study. In addition, in 
the CREDDP, lampreys and other fishes were sampled 
only during fall and winter of a single year; therefore 
we were unable to estimate interannual variability 
in the timing of winter migrations of Pacific lamprey. 
Dedicated, multiyear, lamprey-centric studies with ap- 
propriate gear and sampling schedules would obviously 
be much more effective for collecting lamprey biological 
and ecological data (Moser and Close, 2003). Despite its 
limitations, however, our analysis provides important 
information about lampreys during a life stage about 
which very little is known in the Columbia River estu- 
ary, and it adds to a growing body of knowledge that 
is essential to support the continued existence of these 
ancient species. 
Acknowledgments 
This study benefited from an exceptional field crew, 
which included M. Litz, A. Claiborne, S. Sebring, and A. 
Claxton, and from boat operators B. Kelly and R. Nel- 
son. M. Moser provided encouragement for the project 
and guidance on the identification of lamprey wounds. 
This study was funded by the Northwest Fisheries Sci- 
ence Center and Bonneville Power Administration. The 
manuscript was greatly improved by constructive com- 
ments provided by R. Emmett, M. Moser, and 3 anony- 
mous reviewers. 
5 Cornwell, T. 2014. Unpubl. data. Oregon Dep. Fish 
Wildl., 28655 Hwy. 34, Corvallis, OR 97333. 
