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Fishery Bulletin 106(2) 
have been conducted off the Columbia River, but have 
been limited to one year (Waldron, 1972) and thus it 
was not possible to identify any relationship between 
fluctuations in ocean conditions and changes in the 
ichthyofaunal community. However, Doyle (1995) did 
extensive sampling during spring (April-May), and 
some during other months from 1980-85 and 1987, 
and found distinct changes in the Northwest ichthyo- 
plankton community resulting from the 1983 El Nino. 
Later, Doyle et al. (2002) examined ichthyoplankton in 
the Northeast Pacific, including the Pacific Northwest 
and the Columbia River plume, and identified regional, 
onshore, and offshore differences in the ichthyoplankton 
communities. Northern anchovy was a dominant spe- 
cies off the Pacific Northwest during all these ichthyo- 
plankton surveys. Northern anchovy eggs and larvae 
have been found to be abundant around the Columbia 
River plume (Richardson, 1981; Emmett et ah, 1997). 
However, detailed information on the temporal and 
annual variability of the dominant ichthyoplankton 
components is lacking. This is noteworthy, given the 
importance of larval and postlarval fishes in the diets 
of salmon in the plume region (Schabetsberger et al., 
2003; DeRobertis et al., 2005) and the important role 
that forage fishes, particular northern anchovy, Pacific 
herring ( Clupea pallasi), and smelt, play in the diet of 
piscivorous fishes, mammals, and birds in this region. 
Our study was initiated to provide data to address this 
need, and to further elucidate the early life histories of 
fish species that use the Columbia River plume under a 
variety of environmental conditions. 
Repeated plankton sampling at two stations just 
south of the mouth of the Columbia River over a 6-year 
period provided us an opportunity to study interan- 
nual and seasonal changes in the diversity and species 
assemblages in the nearshore ichthyoplankton com- 
munity of this region. We also identified the effects of 
fluctuating river flows and nearshore oceanic environ- 
mental conditions on the ichthyofaunal community. We 
were provided this opportunity because of the fortuitous 
overlap of our research with the regime change in the 
Pacific Decadal Oscillation (Mantua et al., 1997) in late 
2002 (Goericke et al., 2005). 
Materials and methods 
Study site 
The Columbia River has a diverse drainage basin that 
covers approximately 670,000 km 2 and has average 
flows of approximately 10,000 m 3 /s the latter of which 
create a surface lens, or plume, of low-salinity 
water in the adjacent ocean that can extend 
up to 400 km offshore (Barnes et al., 1972). 
During summer, the plume flows outward and 
southward, but during winter it is confined to 
a narrow band along the Washington coast 
(Anderson, 1972; Hickey and Banas, 2003). In 
summer months the plume is characterized by 
lower salinities (<32 psu), higher turbidities, 
and higher temperatures than the correspond- 
ing variables for surrounding waters and is an 
important habitat for many species of inver- 
tebrates and fishes (DeRobertis et al., 2005; 
Morgan et al., 2005; Emmett et al., 2006). 
Data collection 
Plankton samples were collected at two sta- 
tions approximately every two weeks during 
the spring and summer, as well as occasionally 
during fall and winter in 1999-2004 (Table 1). 
The first station, buoy 1, is located 30 km from 
the mouth of the river and has a bottom depth 
of 98 m. The second station, buoy 2, is located 
20 km from the mouth of the river and has a 
bottom depth of 47 m (Fig. 1). Oblique plankton 
tows to a depth of approximately 40 m were 
conducted with a 1-m diameter net with 335- 
fim mesh and a centrally mounted flow meter. 
The net was washed with seawater after each 
tow, and the contents were preserved in a 10% 
buffered formalin in seawater solution. Any 
large scyphomedusas captured in the net were 
rinsed and removed from the sample. A Niskin 
Figure 1 
Map of the study area showing locations of two buoys off the 
Columbia River, Oregon, where ichthyoplankton was collected 
during survey cruises of the National Oceanic and Atmo- 
spheric Administration, National Marine Fisheries Service, 
1999-2004. Also shown are depth contours (50-500 m) and 
the location of Astoria Canyon. 
