161 
Abstract — Ichthyoplankton samples 
were collected at approximately 
2-week intervals, primarily during 
spring and summer 1999-2004, 
from two stations located 20 and 30 
km from shore near the Columbia 
River, Oregon. Northern anchovy 
( Engraulis mordax) was the most 
abundant species collected, and was 
the primary species associated with 
summer upwelling conditions, but it 
showed significant interannual and 
seasonal fluctuations in abundance 
and occurrence. Other abundant 
taxa included sanddabs (Citharich- 
thys spp. ), English sole ( Parophrys 
vetulus), and blacksmelts (Bathy- 
lagidae). Two-way cluster analysis 
revealed strong species associations 
based primarily on season (before or 
after the spring transition date). Ich- 
thyoplankton abundances were com- 
pared to biological and environmental 
data, and egg and larvae abundances 
were found to be most correlated 
with sea surface temperature. The 
Pacific Decadal Oscillation changed 
sign (from negative to positive) in late 
2002 and indicated overall warmer 
conditions in the North Pacific Ocean. 
Climate change is expected to alter 
ocean upwelling, temperatures, and 
Columbia River flows, and conse- 
quently fish eggs and larvae dis- 
tributions and survival. Long-term 
research is needed to identify how 
ichthyoplankton and fish recruitment 
are affected by regional and large- 
scale oceanographic processes. 
Manuscript submitted 23 August 2007. 
Manuscript accepted 28 January 2008. 
Fish. Bull. 106:161-173 (2008). 
The views and opinions expressed or 
implied in this article are those of the 
author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
Ichthyoplankton community in 
the Columbia River plume off Oregon: 
effects of fluctuating oceanographic conditions 
Maria M. Parnel 
Robert L. Emmett (contact author) 
Richard D. Brodeur 
Email address for Robert L Emmett: Robert.Emmett@noaa.gov 
National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Hatfield Marine Science Center 
2030 S Marine Science Drive 
Newport, Oregon 
The Columbia River and its plume 
form a biologically rich environment. 
It is the largest river flowing into the 
Pacific Ocean in North America (Sher- 
wood et al., 1990), has relatively large 
salmon runs, a healthy white sturgeon 
(Acipenser transmontanus ) population, 
and probably the largest American 
shad ( Alosa sapidissima) run in the 
world. The Columbia River estuary 
is also one of the largest estuaries on 
the west coast (Emmett et al., 2000) 
and supports abundant piscivorous 
marine mammal and bird populations 
(NMFS, 1997; Collis et al., 2002). 
Important marine fisheries located 
in the Columbia River plume include 
those for the following species: Dunge- 
ness crab ( Cancer magister ), salmon 
( Oncorhynchus spp.), and Pacific sar- 
dine ( Sardinops sagax) (Emmett et al., 
2005, 2006). 
River plumes and their associ- 
ated fronts are important habitats 
for fishes during their larval stages 
(Grimes and Funucane, 1991; Govo- 
ni and Grimes, 1992; Govoni, 1997). 
Large freshwater discharges from the 
Columbia River create abrupt ocean- 
ographic fronts that may be impor- 
tant for salmon ( Schabetsburger et 
al., 2003; DeRobertis et al., 2005) 
and other fish species, and they con- 
centrate some species of zooplankton 
(Morgan et al., 2005). The Columbia 
River plume has also been shown to 
be an important spawning and rear- 
ing habitat for some fishes (Richard- 
son, 1981; Doyle et al., 1993, 2002; 
Doyle, 1995; Emmett et al., 1997), 
particularly for the northern stock of 
northern anchovy ( Engraulis mordax) 
(Richardson, 1981). This region also 
has regular upwelling, which is a 
dominant feature of the California 
Current system and in the Columbia 
River plume region, and it ultimately 
determines the amount of primary, 
and probably secondary, production 
within this system (Hickey and Ba- 
nas, 2003). 
Ichthyoplankton surveys have been 
conducted to augment available abun- 
dance data on many commercially 
important fish species and are often 
used to determine spawning biomass 
(Lasker, 1985; Hunter and Lo, 1993) 
as well as to understand recruitment 
processes (Bailey, 1981; Cowan and 
Shaw, 2002). Data sets generated by 
such ichthyoplankton investigations 
provide an opportunity to determine 
the role that oceanographic processes 
and climate change play in recruit- 
ment variability of commercially valu- 
able species. 
There have been relatively few ich- 
thyoplankton surveys conducted off 
the Pacific Northwest. In previous 
ichthyoplankton surveys conducted 
off Oregon, Richardson and Pearcy 
(1977), Brodeur et al. (1985), and 
Auth and Brodeur (2006) identified 
the ichthyofaunal community, but 
these surveys were relatively short 
in duration and the area near the Co- 
lumbia River was not sampled. Oth- 
er coastal ichthyoplankton surveys 
