Weitkamp et al.: Seasonal abundance, size, and host selection of Lampetra ayresii and Entosphenus tridentatus 
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Table 2 
Number of fishes observed with lamprey wounds, by species, in the lower Columbia River estuary 
during the Estuary Purse Seine study during 2008-2012 or 2006-2012 (Chinook salmon only). Also 
provided are the mean percentages of fish of each species with wounds and, for each species, the per- 
centage of cruises in which at least one wounded fish was observed. 
Common name 
Scientific name 
Number of 
fish with 
wounds 
Mean percentage 
of fish with 
wounds 
Percentage of 
cruises with 
wounded fish 
American shad 
Alosa sapidissima 
71 
0.27 
40.0 
Chinook salmon 
Oncorhynchus tshawytscha 
33 
0.84 
37.3 
Shiner perch 
Cymatogaster aggregata 
25 
5.05 
40.7 
Pacific herring 
Clupea pallasii 
8 
0.07 
9.8 
Steelhead 
Oncorhynchus mykiss 
2 
0.19 
7.1 
Longfin smelt 
Spirinchus thaleichthys 
1 
0.19 
4.8 
Sockeye salmon 
Oncorhynchus nerka 
1 
0.42 
6.7 
Surf smelt 
Hypomesus pretiosus 
1 
0.02 
2.2 
was caught (11 of 27 cruises), followed by American 
shad (40%; 16 of 40 cruises), subyearling Chinook 
salmon (37%; 19 of 51 cruises), and Pacific herring 
(10%, 4 of 41 cruises) (Table 2). When the number of 
fish of a particular species with lamprey wounds were 
compared with the total number of individuals of that 
species caught by cruise, the species with the highest 
average percentage of fish with lamprey wounds, by 
cruise, was shiner perch (5.1%), followed by Chinook 
salmon (0.8%), sockeye salmon (0.4%), and American 
shad (0.3%) (Table 2). Wounded fishes and western riv- 
er lamprey were both caught during 11 cruises (but not 
necessarily in the same haul) and were caught together 
in the same haul 5 times, including one western river 
lamprey (144 mm TL) that was observed attached to an 
American shad (127 mm FL) when a net was retrieved. 
There were clear seasonal trends in the frequency of 
fishes observed with lamprey wounds (Fig. 4). Three of 
4 fish species that were frequently wounded (American 
shad, Pacific herring, and shiner perch) displayed the 
highest rates of lamprey wounds in mid-summer. In 
contrast, wound rates for subyearling Chinook salmon 
were highest in September and October, because sever- 
al wounded individuals were observed during time pe- 
riods when relatively few Chinook salmon were caught. 
The maximum wound rate for shiner perch (13.1% of 
individuals caught over a 2-week period were wound- 
ed) was much higher than maximum rates observed for 
other fishes (<2.3%). 
Comparisons of the size of fishes with and without 
wounds indicated apparent size selectivity for small 
American shad but not for other common hosts (Fig. 
5). American shad with lamprey wounds (mean: 113.4 
mm FL; n=6 8) were smaller than those without wounds 
(143.2 mm FL; n=2784) when all cruises were consid- 
ered together (Friedman: Q=14.0, P<0.05). Wounded 
American shad were also smaller than unwounded 
shad when each cruise was evaluated independently, 
although these differences were statistically signifi- 
cant at P<0.10 in only 6 of 15 cruises (KW: Z>1.7) as 
a result of low statistical power. In contrast, there was 
no statistical difference in size between wounded and 
unwounded subyearling Chinook salmon (mean size of 
wounded: 110.9 mm FL, n=33; mean size of unwound- 
ed: 105.1 mm FL, n=2419), Pacific herring (mean size of 
wounded: 115.1 mm FL, n= 8; mean size of unwounded: 
108.0 mm FL, n= 578), or shiner perch (mean size of 
wounded: 95.9 mm FL, n= 24; mean size of unwounded: 
96.8 mm FL, rc=660) (KW: Z<1.5, jP> 0.10; Friedman: 
Q<1.0, P>0.10; Fig. 5). It was notable that the largest 
individuals of commonly wounded species did not have 
wounds: this observation was most pronounced for 
American shad >190 mm FL, but it was also observed 
in Chinook salmon >168 mm FL, and Pacific herring 
>140 mm FL (Fig. 5). 
Discussion 
Lamprey in the Columbia River estuary 
In two studies separated by 20 years both western riv- 
er and Pacific lampreys were caught in the Columbia 
River estuary at similar locations, depths, and seasons. 
Pacific lamprey adults had the highest densities in 
January and February but were present through May 
(Fig. 2), presumably as they moved upstream through 
the estuary during prespawning migration (Moser et 
ah, 2015). Pacific lamprey juveniles were most abun- 
dant in December but were present through June, like- 
ly corresponding with outmigration from riverine rear- 
ing areas (Beamish, 1980). Western river lamprey were 
caught in the estuary from April through September 
(Fig. 2) — a result that is consistent with the concept 
that this species resides and feeds in estuarine habi- 
tats (Beamish, 1980; Bond et al., 1983). Individuals of 
