Harding et at: Regional and seasonal patterns of epipelagic fish assemblages from the central California Current 
273 
the U.S. National Marine Fisheries Service (NMFS) 
along the northern California coast beginning in 2010 
has been expanded well beyond the shelf break to help 
resolve this point. 
During this study ocean conditions in the northern 
CC shifted from a phase of cool, generally produc- 
tive coastal water with strong upwelling and La Nina- 
like conditions (2000-02) to a warmer, less productive 
phase with weaker upwelling and El Nino-like condi- 
tions (2003-05) (Goericke et al., 2005). This gradual 
but progressive shift culminated in a major oceano- 
graphic anomaly in 2005 when upwelling in the north- 
ern CC was delayed by ~2 months, during which time 
sea surface temperatures remained abnormally high 
(Peterson et al., 2006; Schwing et al., 2006). Ecosystem 
effects caused by this delay were dramatic and included 
unusually low chlorophyll (phytoplankton) levels in 
some areas, a crash in recruitment of intertidal mus- 
sels and barnacles, reduction and redistribution of co- 
pepods and other zooplankton, extremely low numbers 
of rockfish larvae, and the complete breeding failure of 
a krill-eating seabird (Peterson et al., 2006; Sydeman 
et al., 2006; Barth et al., 2007). In the epipelagic fish 
community off Oregon, anomalous abundance patterns 
were seen during 2004-05 for northern anchovy, Pa- 
cific sardine, Pacific herring, jack mackerel, osmerids, 
and juvenile salmonids, and several southern species 
were recorded far north of their usual range (Brodeur 
et al., 2006). In the present study we obtained larger 
than average catches of several common species dur- 
ing 2004-05, most notably along the NC. The patterns 
we observed were generally consistent with the catch 
anomalies seen in Oregon (except for juvenile salmon, 
where the above average densities we recorded were 
opposite the Oregon pattern). The years 2004 and 2005 
grouped together weakly in community ordination but 
the hydrographic data we collected at that time failed 
to show a multivariate signal of an anomaly, probably 
because the 2005 climate event was much stronger 
in the northern CC off Oregon and Washington than 
in the central CC off California, and it had a much 
greater effect on more northern fish populations (Pe- 
terson et al., 2006; Schwing et al., 2006). Along the 
NC and especially in the GF, localized oceanographic 
processes operating on smaller (cape-and-bay or less) 
spatial scales may have been more important to the 
community than coastwide climate forcing, at least in 
the short run (i.e., the six-year period of our study) and 
may have masked any broader effects. 
Water origins and transport patterns could account 
for much of the spatiotemporal variability we observed. 
During upwelling-favorable northwest spring winds, 
shelf water transport along the NC is characterized by 
a strong jet that originates in the Pt. Arena upwelling 
center and travels south over the outer shelf and slope 
(20-50 km from the coast), to be deflected offshore by 
Pt. Reyes. Inner shelf water (<20 km from the coast) 
derives from more localized upwelling centers along 
the NC and is transported south past Pt. Reyes but 
more slowly, whereupon it enters GF circulation or is 
entrained offshore (Kaplan and Largier, 2006). When 
upwelling-favorable winds relax, the southward-flowing 
offshore jet slows or stalls, while inner-shelf transport 
reverses direction completely and flows poleward up 
the coast. Gulf water is entrained in these poleward 
flows and travels north around Pt. Reyes toward the 
NC, remaining close to shore with little offshore dis- 
persion until upwelling resumes (Kaplan and Largier, 
2006). This scenario may also predominate in fall, 
when upwelling-favorable winds are generally absent. 
Thus, connectivity between the NC and the GF is punc- 
tuated by alternating water sources and directions of 
nearshore transport, although net transport is to the 
south in most years. In 2004-05 when upwelling was 
weak and delayed, longer periods of poleward transport 
of GF water toward the NC during spring and summer 
may have resulted, perhaps leading to the higher densi- 
ties of clupeiform fishes, jacksmelt, and juvenile salmon 
we observed off the NC during that period. 
In contrast to the NC, water transport and circula- 
tion in the GF (described by Steger et al., 2000) is 
characterized by persistent poleward flow of Pacific 
equatorial water along the shelf break and slope (40 — 
80 km from the coast). Over the shelf (<40 km from the 
coast) circulation is more variable and net transport is 
to the south. The jet of cool upwelled water arriving 
from the NC slows and some portion is captured and 
retained in a coastal cyclonic eddy in the northern and 
eastern GF, where it is sheltered from wind forcing in 
the lee of Pt. Reyes. In the central GF, cross-shelf Ek- 
man transport carries surface water offshore during 
upwelling-favorable periods and onshore during relax- 
ation, and submesoscale (10-50 km diameter) vortices 
are common in all seasons. These circulating features 
transport and mix large volumes of different water 
types within the GF and their presence effectively 
masks any regular seasonal hydrographic patterns in 
some years. Up to four different water masses meet in 
the GF, and the frontal mixing zones between oceanic, 
bay outflow, upwelled cold and upwelled warm water 
have sinuous and shifting locations depending on the 
intensity of wind forcing, river volume, and other vari- 
ables that change seasonally and annually (Schwing et 
al., 1991). Fundamentally different water circulation 
patterns north and south of Pt. Reyes set the GF apart 
as a hydrographically unique location along the north- 
ern California coast (Steger et al., 2000; Largier et al., 
2006). It is also the only coastal region in California to 
receive substantial nutrient enrichment from a major 
fresh water source, here the eutrophic estuarine wa- 
ters of the Sacramento River exiting through the San 
Francisco Bay (Wilkerson et al., 2002). 
Fronts are common ocean features that form where 
distinct water masses collide or opposing currents 
meet. Long bands of concentrated flotsam, plankton, 
and neuston often form at surface convergent fronts, 
sometimes as visible meandering features. The inten- 
sity, persistence, and locations of nearshore fronts cor- 
relate positively with larval fish density (Bjorkstedt et 
al., 2002) and invertebrate recruitment (Roughgarden 
