Weitkamp et al.: Seasonal abundance, size, and host selection of Lampetra ayresii and Entosphenus tridentatus 
215 
Figure 1 
Map of the study area in the lower Columbia River estuary, showing the location of the Columbia River Estuary Data Develop- 
ment Program (CREDDP) trawl and purse seine sites sampled during 1980-1981 and the 4 Estuary Purse Seine (EPS) study sites 
sampled during 2001-2012. Presence of western river ( Lampetra ayresii) and Pacific ( Entosphenus tridentatus) lampreys at each 
station is indicated by shading; A=both species absent; R=western river lamprey only present; P=Pacific lamprey only present; 
B=both species present. The EPS sites were located at Sand Island (SI), Trestle Bay (TB); North Channel (NC); and Desdemona 
Sands (DS). The inset map shows the locations of the Columbia River basin and estuary and Bonneville Dam. State and province 
abbreviations: WA= Washington; OR=Oregon; ID=Idaho; MT=Montana; and BC=British Columbia. 
depths that were shallower during 2001-2002 (mean: 
5.1 m) than during 2003-2012 (mean: 8.9 m) (Table 1). 
Sampling in 2006 was limited to sampling trips in July 
and August at a single station (Trestle Bay). 
During the EPS study, each sampling trip (or cruise) 
consisted of a series of hauls (individual sampling 
events) conducted over 1-4 days. During 2001-2003, 
each station was sampled at least twice during each 
cruise, and, during 2007-2012, 5-9 hauls were made 
at each of the 2 stations during each cruise. Sampling 
gear in the EPS study was restricted to fine-mesh 
purse seines. The purse seine used during 2001-2002 
was shorter and shallower (100 mx4.6 m; area: 796 m 2 ) 
than the seine used during 2003 and 2006-2012 (155 
mxl0.6 m; area: 1912 m 2 ); but the mesh size of both 
nets was identical throughout (stretched mesh open- 
ing: 17 mm; knotless bunt mesh: 15 mm). Two methods 
were used to set the net: 1) during quantitative round 
hauls, it was set in a circle, and 2) in nonquantita- 
tive hauls, it was towed upstream for 10 min before it 
was pursed to increase the catch. Both methods were 
used during a cruise, and a minimum of 6 quantitative 
round hauls were made per cruise. 
Fish processing in the EPS study was similar to 
that in the CREDDP: all fish were identified to species 
and enumerated, a subsample was measured, and the 
remainder were released; eyed lampreys were identi- 
fied by dentition (Hart, 1973). Juvenile Chinook salmon 
( Oncorhynchus tshawytscha) were segregated into 2 
age categories (subyearling [age 0] and yearling [age 
1]) on the basis of seasonally adjusted fish length cut- 
offs (Weitkamp et al., 2012) because subyearling and 
yearling Chinook salmon differ in many life history 
traits, including degree of estuarine residency (Quinn, 
2005). 
Although the catch of lampreys was recorded in all 
years, recognizing and recording lamprey wounds on 
fishes did not begin until 2008 for all fishes or 2006 
for juvenile salmon. We tallied only the fresh wounds 
that we were confident were due to lamprey predation 
because of their shape (circular or oval) and location 
on the body (back or sides) (Cochran, 1986; Beamish 
and Neville, 1995; Siwicke, 2014); scars (wounds with 
healed skin) were excluded. All the lamprey wounds 
that we identified were classified as type A, stage 
I or II (King, 1980): wounds with broken skin that 
exposed the underlying musculature and occasionally 
wounds with active bleeding. Verification that observed 
wounds were likely due to lamprey predation was con- 
firmed from photographs by Moser 3 . Because of time 
constraints, the presence of lamprey wounds on a fish 
was recorded but details about wound location or depth 
were not collected (e.g., Orlov et al., 2009; Siwicke, 
2014). Other common wounds observed on fishes in- 
cluded those due to marine mammals, avian predators, 
or unknown sources. 
Data analysis 
Our analysis was twofold: 1) we evaluated annual oc- 
currence, seasonal abundance, and size (using CRED- 
DP and EPS data) and the distribution (using CRED- 
3 Moser, M. 2012. Personal commun. Northwest Fish. Sci. 
Cent., Natl. Mar. Fish. Serv., 2725 Montlake Blvd. E., Seattle, 
WA 98112-2097. 
