510 
Abstract — Stomach samples from 
three rockfish species, yellowtail 
( Sebastes flavidus), widow (S. ent- 
omelas), and canary (S. pinniger) 
rockfish, seasonally collected off the 
Pacific Northwest in 1998 and 1999, 
provided quantitative information 
on the food habits of these species 
during and after the 1997-98 El Nino 
event. Although euphausiids were the 
most common major prey of all three 
predators, gelatinous zooplankton 
and fishes were the most commonly 
consumed prey items during some 
seasonal quarters. The influence of 
the El Nino event was evident in the 
diets. Anomalous prey items, includ- 
ing the southern euphausiid species 
Nyctiphanes simplex and juveniles of 
Pacific whiting ( Merluccius productus) 
frequently appeared in the diets in 
the spring and summer of 1998. The 
results of stomach contents analyses, 
based on 905 stomach samples from 49 
trawl hauls during seven commercial 
fishing trips and from 56 stations 
during research surveys, were consis- 
tent with the timing of occurrence and 
the magnitude of change in biomass 
of some zooplankton species reported 
from zooplankton studies in the north- 
ern California Current during the 
1997-98E1 Nino. Our findings indi- 
cate that the observed variations of 
prey groups in some rockfish diets 
may be a function of prey variability 
related to climate and environment 
changes. 
Manuscript submitted 21 November 2008. 
Manuscript accepted 30 July 2009. 
Fish. Bull. 107: 510-522 (2009). 
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. 
Dietary variations in three co-occurring 
rockfish species off the Pacific Northwest during 
anomalous oceanographic events in 1998 and 1999 
Yong-Woo Lee (contact author) 
David B. Sampson 
Email address for contact author: Yongwoo.Lee@dfw.wa.gov 
Coastal Oregon Marine Experiment Station 
and Department of Fisheries and Wildlife 
Hatfield Marine Science Center 
Oregon State University 
Newport, Oregon 97365 
Present address for contact author: Washington Department of Fish and Wildlife 
600 Capitol Way North 
Olympia, Washington 98501 
Numerous rockfish species inhabit 
the waters off California, Oregon, and 
Washington. At least 69 species are 
found in the northeast Pacific Ocean 
(Love et al., 2002). Although many of 
these species have been an important 
part of the commercially exploited 
groundfish in this region, rockfish 
harvests off the U.S. West Coast have 
been greatly curtailed in recent years 
because several stocks were assessed 
as being severely depleted (Parker 
et al., 2000). Despite the economic 
importance of these species, we have 
limited knowledge of their behavior 
and ecology, including how the individ- 
ual species interact within the coastal 
ecosystem. Detailed knowledge about 
the ecological behavior of fish species, 
especially their food habits, is essen- 
tial for developing ecosystem-based 
approaches to fisheries management 
because such information will pro- 
vide the linkages between the fish spe- 
cies in multispecies stock assessment 
models (Livingston, 1985; Livingston 
and Jurado-Molina, 2000). 
During the unusual oceanographic 
events of the 1997-98 El Nino and the 
subsequent cooling phase called La 
Nina in 1999, we collected informa- 
tion on the food habits of three com- 
mercially important rockfish species, 
yellowtail ( Sebastes flavidus ), widow 
(S. entomelas), and canary (S. pin- 
niger) rockfish. Although the diets of 
these species off the west coast of the 
United States were examined in two 
previous studies (Brodeur and Pearcy 
1984; Adams 1987), neither study was 
conducted during anomalous oceano- 
graphic events such as El Nino and 
La Nina years as observed in the 
current study. Most other studies of 
rockfish food habits have focused on 
shallow-water species or have been 
limited in the geographic and tempo- 
ral range of their sample collections. 
The current study not only updates 
our knowledge of rockfish food hab- 
its over wide geographic and tempo- 
ral ranges but also examines their 
dietary variations during periods of 
major environmental change. 
Since 1950 there have been seven 
strong El Nino occurrences (http:\\ 
www.elnino.noaa.gov; accessed July, 
2009). The recent event (1997-98) is 
considered the first or second stron- 
gest El Nino in the 20 th century, com- 
parable to the record 1983 El Nino 
(McPhaden, 1999). Peterson et al. 
(2002) reported changes in the spe- 
cies composition and biomass of the 
copepod community during El Nino 
of 1997-98 off central Oregon and 
found that warm-water copepod spe- 
cies dominated the community during 
this period. Alternations in the zoo- 
plankton community and the unusual 
occurrence of southern zooplankton 
species were noted in the northern 
coastal waters off Oregon and Brit- 
ish Columbia during the same period 
