146 
Fishery Bulletin 106(2) 
spawning that occurred around high tide was equiva- 
lent to the ratio of high tides that occurred within the 
fundamental diel spawning period (1 hour before to 3 
hours after sunset). 
Sound production 
The sound production rate of white seabass peaked in 
May, averaged 29.2 sounds/min, and reached a minimum 
average of 1.5 sounds/min (primarily hydrodynamic 
booms) in December (Fig. 4). Sound production rates 
were significantly greater on 24-h recordings made 
during the spawning season (mean=12.7 sounds/min) 
than during months without spawning (mean = 4.5 
sounds/min) (/=4.88, df=118, P>0.001). Within the 
spawning season, there was a significant increase in 
the rate of sound production on spawning than on non- 
spawning days (/= 9.23, df=203, P>0.001), and peak rates 
occurred during spawning events (Fig. 5). Similarly, a 
significant increase in sound intensity was observed for 
sounds recorded on spawning days than 
on nonspawning days (f=1.89, df=438, 
P=0.030). 
The basic sound types that have been 
identified for the white seabass are single 
pulse-trains, multiple pulse-trains, drum- 
rolls, thuds, and hydrodynamic booms 
(Fig. 6). A rapid succession of overlapping 
drum-roll and thud sounds resulted in 
recognizable spawning chants during the 
release of gametes. All sound types oc- 
curred on days of spawning; however, only 
hydrodynamic booms along with single 
and multiple pulse-trains of reduced rate 
and intensity occurred on days with no 
spawning (Fig. 7, A and B). 
Single pulse-trains increased in rate 
and intensity on audio recordings that 
corresponded with spawning. The rate 
and intensity of pulse-trains remained 
high between successive spawning events 
and throughout the 1-h period after 
spawning. 
Multiple pulse-trains occurred as a se- 
ries of two to six pulse-trains, typically 
in a rhythmic pattern every 4-6 seconds. 
Weak multiple pulse-trains were detected 
throughout the day during the spawn- 
ing season, but sound intensity greatly 
increased during the 90-min period after 
spawning events (Fig. 7B). Post-spawn- 
ing multiple pulse-trains were of higher 
intensity than any other type of white 
seabass sounds. 
Drum-rolls and thuds increased in 
rate and intensity during the initiation 
of spawning behavior and were not detect- 
ed outside of the 4-h period surrounding 
spawning. Drum-rolls and thuds occurred 
in repetitive trains and were categorized 
as abbreviated chants or spawning chants 
when overlapping sounds became audibly 
indistinguishable. 
Abbreviated chants consisted of rap- 
id sequences of drum-rolls and thuds 
that terminated abruptly after 3-5 sec 
of spawning behavior and there was no 
release of gametes. Abbreviated chants 
were shorter in duration and lower in in- 
tensity than spawning chants and were 
35% ■ 
30% 
25% 
20 % ■ 
1 5 % ■ 
10% 
0=174 
5% 
0% 
-2 -1 Sunset +1 +2 +3 
Hours in relation to sunset 
+4 
+5 
45% i g 
40% - 
35% - n=155 
30% - 
25% - 
20 % - 
15 % - 
10 % - 
5% - 
0% 
17:00 18:00 19:00 20:00 21:00 22:00 
Pacific standard time (h) 
23:00 
Figure 2 
The percent occurrence of white seabass (Atractoscion nobilis) spawning 
events illustrating diel spawning periodicities (A) in relation to sunset 
and (B) according to Pacific Standard Time for 2001-03. Sample sizes 
correspond to the number of spawning events that could be assigned 
to an hourly interval. (A) Dashed line depicts the time of sunset and 
shading represents diminishing light levels throughout the evening. 
There is no shading in (B) because of seasonal changes in the time 
of civil twilight. 
