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Fishery Bulletin 113(2) 
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Figure 5 
Comparison of the size frequency of (A) American shad ( Alosa sapidissima), (B) Chinook salmon 
(Oncorhynchus tshawytscha), (C) shiner perch ( Cymatogaster aggregata), and (D) Pacific herring 
( Clupea pallasii), with and without lamprey wounds. These fishes were collected in the lower Co- 
lumbia River estuary during 2008-2012 or 2006-2012 (Chinook salmon only). 
2009), given the often incorrect assumption that all ju- 
venile lampreys are Pacific lamprey (Kostow 1 ; Mesa 
and Copeland, 2009) and the difficulties of identifying 
small ammocoetes to species (Goodman et al., 2009). 
The catch of each lamprey group (western river lam- 
prey and Pacific lamprey juveniles and adults) in the 
CREDDP study was different with gear type, and the 
variation between groups due to gear type was mir- 
rored by purse seine catches in the EPS study. In the 
CREDDP, catches of adult Pacific lamprey were more 
frequent in purse seines than in trawls, Pacific lam- 
prey juveniles were caught more often in trawls than 
in purse seines, and catch of western river lamprey 
was fairly even between the 2 gear types (Table 1, Fig. 
2). Accordingly, the near absence of Pacific lamprey in 
the EPS study was more likely due to a lack of sam- 
pling in winter and early spring, when the species was 
most abundant, and to an exclusive use of purse seines, 
which caught few juveniles, than due to low densities. 
These gear-specific differences likely reflect the loca- 
tion of lampreys (or their hosts) in the water column. 
Higher catches of Pacific lamprey juveniles in bottom 
trawls, compared with catches in purse seines, indicate 
that this species is demersal (or attached to demersal 
hosts), in contrast to Pacific lamprey adults and west- 
ern river lamprey (or their hosts), which were read- 
ily caught by pelagic purse seines. In addition, several 
studies also have shown that catches of lampreys in- 
crease with water depth (e.g., Dawley et al. 4 , Beamish 
and Youson, 1987). This habitat preference may be 
responsible for the absence of lampreys during 2001- 
2002 in the EPS study, when depth at sampling sites 
was shallower than depths at sites during 2003-2012, 
and for low catches (4 individuals) in shallow fyke nets 
and beach seines during the CREDDP study. Whether 
lampreys are attached to hosts or free swimming at 
these life history stages and how these behaviors vary 
geographically within and between estuaries must be 
determined to understand lamprey habitat use and re- 
quirements in estuaries. 
The average sizes that we report for Pacific lam- 
prey adults (596 mm TL) and juveniles (133 mm TL) 
