148 
Fishery Bulletin 106(2) 
Average total sound production rate (sounds/min) 
Figure 5 
Mean sound production rate (±1 standard error) of white seabass 
( Atractoscion nobilis) for all combined sound types in relation to the 
release of gametes during 3-min evening recordings (n = 102) when 
spawning was documented from March to July 2003. The term “Inter” 
refers to the period between successive spawning events. The time 
between successive spawning was 1 to 98 min (mean = 31 min). 
1500 
1000 
500 
300 
200 
100 
50 
20 
D 
0.0 
Hydrodynamic boom 
Time (s) 
Figure 6 
Three-second sonograms of five basic sound types (A, B, D) gen- 
erated by white seabass ( Atractoscion nobilis), in addition to an 
identifiable spawning chant (C) consisting of overlapping drum-roll 
and thud sounds generated during the release of gametes. Modified 
from Aalbers and Drawbridge (in press). 
Taylor and Villoso, 1994) and in many 
fish species worldwide (Johannes, 1978). 
Spawning during low-light conditions may 
occur to reduce predation rates on both 
freshly spawned eggs and spawning adults 
(Lobel, 1978; Holt et ah, 1985). Broadcast 
spawners may further benefit from syn- 
chronizing spawning activity by temporally 
concentrating reproductive effort and maxi- 
mizing time allocated for diurnal movements 
and feeding. 
Lunar spawning 
White seabass spawned throughout the lunar 
cycle; although more individuals may have 
achieved reproductive readiness following 
the new moon, because 63% of mass spawn- 
ing events occurred from the new moon until 
four days after the new moon. The major- 
ity of known lunar spawning periodicities 
occur around the new or full moon, possibly to 
reduce egg predation through increased dis- 
persal around larger tidal flows or to ensure 
that males and females collectively achieve 
reproductive readiness (Johannes, 1978). 
Environmental conditions 
The majority of spawning occurred as water 
temperature and photoperiod increased 
during the spring and early summer; these 
factors appear to be important in stimulat- 
ing white seabass spawning activity. Most 
spawning occurred at water temperatures 
between 15 and 18°C; this range is consistent 
with that observed under hatchery protocols 
to artificially induce spawning in broodstock 
tanks. Although more spawning was docu- 
mented around high tide, this effect can be 
attributed to the increased occurrence of eve- 
ning high tides during summer within the 
mixed semidiurnal tide regime of southern 
California (Flick, 2000). 
Experimental variables 
Although variations in the onset and dura- 
tion of spawning seasons and the number of 
spawning events per season may represent 
biological responses to shifting environmen- 
tal conditions (e.g., temperature changes), 
differences may be partly attributed to 
research procedure. The captive population 
was 34% lower in 2001 because 21 white 
seabass were not combined with the origi- 
nal 41 fish until after the 2001 spawn- 
ing season. Additionally, increases in fish 
size and acclimation time over the 3-year 
period may have been responsible for the 
