Aalbers and Sepulveda: Seasonal movement patterns and temperature profiles of adult Atractoscion nobilis off California 
11 
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 
Month 
Figure 7 
The percent occurrence of all depth values <5 m plotted by month to il- 
lustrate periods of surface-oriented behavior for 33 adult white seabass 
( Atractoscion nobilis) tagged and released off California and Baja Califor- 
nia, Mexico, from 2008 to 2011. 
cycle at regular intervals over prolonged time periods 
(days to months). If this basic assumption of the FFT 
algorithm has not been met, then discontinuity would 
disperse energy throughout all frequencies (cpd), caus- 
ing considerable noise in the spectral density plots. 
Additional analyses from tracks of multiple individual 
fish with extended time-series records may further 
identify rhythms in vertical movements on a monthly 
(lunar) or seasonal scale. 
Increased VROM values around dusk and dawn in- 
dicate heightened crepuscular activity throughout the 
year. Heightened feeding activity in other fishes and 
sharks has been associated with crepuscular periods 
as well as with instances of increased vertical activity 
(Kitagawa et al., 2004, Sepulveda et ah, 2004, Best- 
ley et ah, 2008). Higher rates of crepuscular activ- 
ity indicate that white seabass are effective low-light 
predators and support fishery information that white 
seabass are targeted most effectively by hook-and-line 
fishermen during crepuscular periods (Pfleger 7 ). Be- 
cause the spawning activity of white seabass peaks 
just after sunset during the spring and summer 
months (Aalbers, 2008), the increased VROM around 
dusk may also correspond with vertical excursions as- 
' Pfleger, T. 2010. Personal commun. Pfleger Institute of 
Environmental Research, 2110 South Coast Hwy., Oceanside, 
CA 92054. 
sociated with spawning-related behavior and broadcast 
spawning events (Aalbers and Drawbridge, 2008). In 
contrast, diel surface-oriented behavior was observed 
most consistently during the midday (0900-1600 PST) 
and predawn (2300-0300 PST) hours, timing that co- 
incided with periods of reduced vertical activity (Fig. 
6, A and B). Surface-oriented behavior has also been 
described for white seabass during courtship periods 
within the hours preceding sunset (Aalbers and Draw- 
bridge, 2008), periods when fish may be more vulner- 
able to spear fishermen and surface gill nets. 
Horizontal movements 
It was not uncommon for individuals to move more 
than 500 km from their initial point of release, veri- 
fying that white seabass are a highly mobile coastal 
species. A 109-cm-TL female travelled a net distance 
of 555 km over a 76-day period from Santa Catalina 
Island to Monterey Bay, California, at a rate of 8 km 
day -1 . Collectively, a mean displacement of 229 km 
from the initial tagging location indicates that white 
seabass are capable of extensive seasonal migrations. 
Widespread horizontal movements during the spawn- 
ing season are consistent with recent data that indi- 
cate limited residency periods at distinct spawning 
sites along the southern coast of California (Aalbers 
and Sepulveda, 2012). The broad movements docu- 
