Laidig: Influence of ocean conditions on the timing of early life events for Sebastes mystmus 
447 
145.0 i 
140.0 - 
« 135.0 H 
E 130.0 - 
® 
a> 
Z 125.0 - 
to 
( 1 ) 
D) 
120.0 - 
> 1 15.0 H 
< 
110.0 H 
105.0 
♦ Mendocino 
■ Monterey 
1993 1994 
# 
2001 2002 
2003 
Year 
Figure 7 
Average age at settlement, calculated from otolith data, for blue rockfish 
( Sebastes mystinus) from two study areas off California. Black stars indicate 
significant differences (P<0.05). Dashed lines represent the 5-year average 
for each site. Vertical bars represent one standard error. 
(Wyllie-Echeverria, 1987). Plaza et 
al. (2004) determined that parturi- 
tion of S. inermis occurred later in 
the season at the more northerly sites 
in the western Pacific and suggested 
that this difference may be related 
to environmental cues. Vinagre et al. 
(2008a, 2008b) reported a latitudi- 
nal gradient in time of spawning for 
European sea bass (Dicentrarchus 
labrax ) and common sole ( Solea solea) 
off Portugal and that spawning onset 
occurs earlier in the south. These re- 
searchers suggested that warm wa- 
ter temperatures in winter at lower 
latitudes or differences in photoperiod 
may influence the onset of spawning. 
The latitudinal difference in the 
timing of settlement and parturition 
in blue rockfish could be an adap- 
tation by blue rockfish to oceanic 
conditions. Bograd et al. (2009) cal- 
culated the spring transition index 
(i.e., the beginning of the upwelling 
season) and found that upwelling be- 
gan on average 20 days earlier off 
Monterey than off Mendocino. This 
difference is similar to the 23-day 
average difference in settlement 
timing between these two areas. It 
is possible that blue rockfish have 
adapted to this difference in the timing of upwelling. 
Interannual variability in parturition dates has been 
noted by researchers, but specific causes for this vari- 
ability are still unknown. Woodbury and Ralston (1991) 
observed variations in the timing of parturition for five 
species of rockfishes over six years. Early parturition 
dates have been related to increased maternal age and 
size for some rockfish species (Bobko and Berkeley, 
2004; Plaza et al., 2004; Sogard et al., 2008). Plaza et 
al. (2004) proposed that the time of parturition could be 
influenced by effects of temperature on gestation times. 
Carr (1991) suggested that upwelling may influence the 
time of parturition. Interestingly, positive upwelling in 
January and February in this study was correlated with 
settlement date and this finding strengthens Carr’s 
speculation. 
Interannual variability in settlement date was re- 
lated to upwelling and sea level height in this study. 
Settlement occurred later in years when upwelling 
was stronger and sea level anomaly was negative (i.e., 
there was an equatorward flow of cold water). Stron- 
ger upwelling may have transported juvenile rockfish 
farther offshore, making their return to the nearshore 
more difficult and causing successful recruitment to 
occur later in the season (Ainley et al., 1993; Larson 
et al., 1994; Sakuma et al., 2006; Wilson et al., 2008). 
Years with reduced or negative upwelling should re- 
sult in onshore transport and thus earlier settlement 
to nearshore areas. Cold water produced by upwelling 
or flow from the north may result in slow growth of 
juvenile rockfishes (Boehlert and Yoklavich, 1983). 
These slow-growing individuals may migrate slowly 
to the nearshore environment. If prey are plentiful, 
the fish may remain in these food-rich waters longer 
or, if the quality of the prey items was low, the fish 
may exhibit reduced growth rates (Boldt and Rooper, 
2009). Both of these factors could lead to later settle- 
ment of individuals. 
Large-scale oceanographic processes (covering 
100s of kilometers) can be important in determin- 
ing recruitment strength over a broad area. Field 
and Ralston (2005) concluded that the synchrony in 
year-to-year recruitment for three rockfish species 
along the west coast of North America was caused 
by large-scale ocean processes (i.e., El Nino and Pa- 
cific Decadal Oscillation). Ralston and Howard (1995) 
reported similar recruitment strengths in blue and 
yellowtail rockfishes from two areas off California 
over a 10-year period and suggested large-scale ocean 
processes that affect sea surface temperatures (such 
as El Nino) are primarily responsible for the recruit- 
ment variation. Laidig et al. (2003) estimated simi- 
lar ages and growth curves for adult blue rockfish 
from Mendocino and Monterey, which indicated that 
the fish from these areas are influenced by similar 
oceanographic conditions. 
Understanding the causal relationship of biologic 
and oceanographic factors on recruitment dynam- 
