Weitkamp et al.: Seasonal abundance, size, and host selection of Lampetra ayresii and Entosphenus tridentatus 
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Table 3 
Comparison of the total lengths of Pacific lamprey (Entosphenus tridentatus) adults and juveniles and 
western river lamprey (Lampetra ayresii) reported in the literature and observed in our analysis of data 
sets from studies in the lower Columbia River estuary during 1980-1981 and 2001-2012. -=no data 
were available. 
Species and location 
Mean length 
(mm) 
Range 
(mm) 
Source 
Pacific lamprey adults 
Columbia River estuary 
596 
401-745 
This analysis 
Columbia River, John Day River 
- 
610-725 
Bayer et al. 1 
British Columbia rivers 
190-640 
130-720 
Beamish, 1980 
Fraser River, British Columbia 
337 
273-453 
Beamish and Levings, 1991 
Puget Sound rivers 
227 
194-274 
Hayes et al., 2013 
Oregon & N. California 
516 
393-620 
Kan, 1975 
California rivers 
- 
300-760 
Moyle, 2002 
Santa Clara River 
593-610 
485-800 
Chase, 2001 
Pacific lamprey juveniles 
Columbia River estuary 
133 
102-157 
This analysis 
British Columbia rivers 
120-140 
47-160 
Beamish, 1980 
Fraser River, British Columbia 
106-140 
- 
Beamish and Levings, 1991 
Skeena River, British Columbia 
- 
115-155 
Farlinger and Beamish, 1984 
Puget Sound rivers 
125 
- 
Hayes et al., 2013 
Tenmile Creek, Oregon 
- 
130-140 
van de Wetering, 1998 
Oregon rivers 
120 
96-155 
Kan, 1975 
Western river lamprey 
Columbia River estuary 
198 
102-324 
This analysis 
Columbia River estuary 
158-268 
115-310 
Bond et al., 1983 
Fraser River 
114 
40-190 
Beamish, 1980 
Strait of Georgia 
227 
100-290 
Beamish, 1980 
Puget Sound rivers 
154 
104-277 
Hayes et al., 2013 
Yaquina Bay, Oregon 
179-218 
133-255 
Bond et al., 1983 
California rivers 
- 
250-310 
Moyle, 2002 
1 Bayer, J. M., T. C. Robinson, and J. G. Seelye. 2000. Upstream migration of Pacific lampreys in the 
John Day River: behavior, timing, and habitat use, 46 p. Bonneville Power Administration Report DOE/ 
BP-26080-1. [Available from https://pisces.bpa.gov/release/documents/documentviewer.aspx?doc=26080-l] . 
and for western river lamprey (198 mm TL) are gen- 
erally larger than the sizes reported for populations 
from British Columbia to California (Table 3). However, 
direct comparisons are challenging because of rapid 
growth during some life history stages and declines 
in size (shrinking) during others, along with variation 
in distances of sampling locations from the ocean. Our 
maximum measured lengths for adult Pacific (745 mm 
TL) and western river lamprey (324 mm TL) were near 
or larger than the maximum sizes reported by common 
fish identification guides (e.g., Hart, 1973; Mecklenburg 
et al., 2002; Wydoski and Whitney, 2003), indicating 
that the Columbia River estuary may have unusually 
large individuals of both species. Adult Pacific lamprey 
in the Columbia River with longer migrations tend to 
be larger than adults with shorter migrations (Kan, 
1975; Keefer et al., 2009) — a relationship that has a 
strong genetic basis (Hess et al., 2014). Consequently, 
although the larger size of Pacific lamprey in the Co- 
lumbia River than the size of Pacific lamprey in other 
rivers may be explained by genetic adaptations to long 
migrations, it remains unclear whether similar adap- 
tations or other factors, such as older age at maturity, 
are responsible for the large size of western river lam- 
prey in the Columbia River estuary. 
Fishes with lamprey wounds 
We observed lamprey wounds on 8 species of fishes in 
the Columbia River estuary. We believe the majority of 
these wounds resulted from predation by western river 
lamprey, rather than by Pacific lamprey, because of 1) 
the seasonal overlap with western river lamprey and 
apparent absence of juvenile Pacific lamprey during 
summer, 2) wound locations on the dorsal surfaces of 
fishes (versus ventral surfaces for predation by Pacific 
lamprey; Beamish, 1980; Cochran, 1986; Clemens et al., 
2010), and 3) wounds that were elongated rather than 
circular and did not completely penetrate the muscle 
layer (Fig. 3; Beamish, 1980; Beamish and Neville, 
1995; Murauskas et al., 2013). We observed no wounds 
that we were confident were due to Pacific lamprey. 
