Aalbers and Sepulveda: Seasonal movement patterns and temperature profiles of adult Atractoscion nobilis off California 
5 
Percent occurrence 
A 0 5 10 15 20 25 30 
Temperature (°C) 
Figure 1 
Frequency distributions showing collective (A) depth and (B) temper- 
ature profiles for 33 adult white seabass ( Atractoscion nobilis) that 
were tagged and recaptured along the California and Baja California, 
Mexico, coastlines during 2008-2011. Observations are based on depth 
bins of 5 m by 2 min and temperature bins of 1°C by 4 min. 
temperature records at resolutions of 2 min and 4 min. 
Fish at liberty for periods of up to 1572 days (mean=468 
days) provided comprehensive multiyear data sets for 
an evaluation of seasonal and interannual patterns of 
depth distribution and habitat use. 
Vertical movements 
The cumulative mean depths during the daytime, 
nighttime, and twilight periods were 14.9 m (SD 5.1), 
15.5 m (SD 5.1), and 16.8 m (SD 6.8), respectively. Brief 
vertical excursions to depths up to 245 m were record- 
ed; however, 95% of all the recorded depths were <50 
m (Fig. 1A). Monthly mean depth values of tagged fish 
revealed that the fish remained significantly deeper in 
the water column between October and March (paired 
£-test: £=14.41, P<0.0001) than between April and Sep- 
tember, reaching a maximum mean depth of 31.1 m (SD 
13.2) in January (Fig. 2). Depth profiles were shallower 
on average as water temperatures increased during the 
spring and summer months, reaching a minimum mean 
depth of 10.5 m (SD 7.3) in August (Fig. 2). 
Although diel and seasonal depth patterns were con- 
sistent among most fish, individual variability and in- 
terannual trends were apparent from mean daily depth 
and temperature profiles (Fig. 3, A and B). For exam- 
ple, fish A06097 remained consistently deeper (27.0 m 
[SD 13.5]) than all other white seabass (9.4 m [SD 4.5], 
7i- 4) during the summer months of 2010. In compari- 
son, fish A03591 occurred at roughly half (14.4 m [SD 
3.7]) of the mean depth observed for all other fish (28.9 
m [SD 4.5], n=l ) during the winter months of 2009- 
2010. Although A03591 was the largest female (152 cm 
TL) tagged during this study, a consistent correlation 
was not found between fish size and mean depth, fish 
size and mean temperature, or sex and mean depth. 
Mean depth and temperature from August to October 
in 2010 were considerably less for 5 individuals recap- 
tured within Monterey Bay than for all other fish re- 
captured in other areas: 8.7 m and 13.6°C versus 13.0 
m and 15.4°C. 
Depth probability plots constructed for each month 
represented seasonal shifts in depth, indicating more 
surface-oriented distributions evident from April to 
October, transitional periods during March and No- 
vember, and deeper profiles from December to Feb- 
ruary (Fig. 4, A-D). Fish showed more of a bimodal 
depth distribution during transitional periods, with 
peaks in cumulative probability near 10 m as well 
as at depths between 15 and 30 m (Fig. 4, B and D). 
