Aalbers: Spawning periodicities of Atractoscion nobilis 
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Boom P-T Mult. P-T Thud 
Sound type 
Drumroll A. chant Chant 
Figure 7 
(A) The mean rates (±1 standard error) and (B) mean relative sound pres- 
sure levels (dB rms [root mean square] values do not represent absolute 
sound pressure level) of white seabass ( Atractoscion nobilis) sounds for all 
3-min evening recordings (n = 151) made from March through July 2003. 
Recordings are grouped by period of occurrence in relation to the time of 
spawning or categorized as “no spawning” on evenings that spawning did not 
occur. Prespawning intervals spanned the 2-h period before initial spawn- 
ing; postspawning intervals spanned the 2.5-h period after final spawning 
events; interspawning intervals spanned the period between successive 
spawning events, which occurred 1 to 98 minutes apart (mean=31 min). 
(P-T=pulse-train, Mult. P-T=multiple pulse-trains, A. chant = abbreviated 
chant, Chant = spawning chant). 
46% increase in observed spawning 
activity in 2003 compared to 2001. 
Improved recognition of fish behav- 
iors and patterns likely enhanced the 
detection of spawning events in 2002 
and 2003. Difficulty in differentiat- 
ing successive spawning events solely 
on the presence of eggs considerably 
reduced the total number of docu- 
mented events, along with an inabil- 
ity to visually detect spawning after 
dark. Variations in white seabass feed 
rations may have influenced interan- 
nual spawning activity because con- 
dition factor influences fecundity in 
weakfish ( Lowerre-Barbieri et al., 
1996), haddock ( Melanogrammus 
aeglefinus) (Hislop et al., 1978), and 
Atlantic cod ( Gadus morhua) (Kjesbu 
and Klungsoyr, 1991). 
Spawning frequency 
Although data were not extensive 
enough to accurately determine indi- 
vidual white seabass spawning fre- 
quency or fecundity, it was apparent 
that females are serial spawners. The 
average number of observed spawning 
events per female in 2001, 2002, and 
2003 was 2.0, 3.1, and 2.1, respectively; 
however, these values are underesti- 
mated because of experimental limita- 
tions. The same female spawned on 12 
June 2002 between 2010 h and 2040 
h and again on 16 June 2002 at 2038 
h, indicating a capability for four-day 
spawning intervals. 
The observed shift in the diel 
spawning periodicity in relation to 
sunrise and sunset as the spawn- 
ing season progressed indicates that 
final oocyte maturation is not trig- 
gered solely by light intensity or the 
time of sunrise and sunset. White 
seabass exhibited a more consistent 
24-h diel spawning pattern throughout the season, 
indicating that gamete development may occur with 
a circadian rhythm that could be modified through 
a combination of environmental cues (Taylor, 1984). 
Spawning rhythms and gamete development fluctu- 
ate synchronously with plasma estradiol-17/3 levels 
in female spotted seatrout and with testosterone and 
llketotestosterone concentrations in males (Brown- 
Peterson, 2003). In addition to regulating seasonal 
and diel spawning rhythms, increases in the levels of 
plasma androgens are correlated with seasonal hyper- 
trophy of sonic musculature as male weakfish come 
into spawning condition (Connaughton and Taylor, 
1994; Connaughton et al., 1997). 
Sound patterns 
White seabass may experience alterations in repro- 
ductive endocrine hormones and physiological features 
that are similar to those observed in other sciaenids, 
because peak diel and seasonal spawning rhythms were 
directly correlated with increases in the rate, intensity, 
and variety of sound production. Sound production in 
orangemouth corvina and weakfish also culminates 
seasonally during peak spawning in May and diminishes 
in late July as spawning subsides (Fish and Cummings, 
1972; Connaughton and Taylor, 1995). Additionally, diel 
increases in the sounds of weakfish and spotted seatrout 
have been documented after sunset during hours of 
