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Fishery Bulletin 106(2) 
have only been described in the white seabass (Aalbers 
and Drawbridge, in press). 
Acoustically monitoring the sounds produced by 
spawning fish can reveal the periodicity and critical 
habitat of spawning aggregations and help managers 
in the development of fishery regulations and in the 
better placement of marine protected areas (Luczkov- 
ich et ah, 1999). However, patterns of spawning-related 
sound production must be established in order to yield 
meaningful results for such application. The objective 
of this investigation was to determine the spawning 
periodicities and associated sound production patterns 
of white seabass under seminatural environmental 
conditions. This study presents a comprehensive as- 
sessment of sciaenid sound production as it relates 
to known spawning activity and establishes the foun- 
dation from which passive acoustic surveys can be 
conducted. 
Materials and methods 
Sampling locations and procedures 
Research was conducted from an aquaculture platform 
consisting of four 9x9x6. 5-m net pens moored in Cata- 
lina Harbor, Santa Catalina Island, CA. Forty-one adult 
white seabass were transported live to an individual 
net pen (526 m 3 ) from March through June 2000. An 
additional 21 fish, collected in May 2001, were excluded 
from the 2001 spawning data while being acclimated in 
a separate net pen. In October 2001, all fish were mea- 
sured to the nearest mm, weighed to the nearest 10 g, 
examined to determine sex, tagged with a passive inte- 
grated transponder (PIT; Avid, Greeley, CO), and com- 
bined into a single net pen. Forty-seven female and 15 
male fish ranged in initial size from 83 to 126 cm total 
length (TL) and 4.9 to 19.5 kg in weight. Fish were only 
manipulated when remeasured in February 2003 and 
no mortality occurred during the study. Captive white 
seabass were fed variable rations of freshly caught squid 
(Loligo opalescens), chub mackerel (Scomber japonicus), 
and jack mackerel (Trachurus symmetricus ) as they 
became available locally. 
Documentation of spawning 
Fish spawning periodicity was assessed from 2001 to 
2003 by direct observation from an elevated deck, by 
sampling the net pen for freshly spawned eggs with a 
500-pm-mesh dip net, and by acoustically monitoring 
fish sounds. Successive spawning events were difficult 
to differentiate from egg sampling alone; therefore mul- 
tiple spawning events were documented only if visually 
observed or acoustically detected and accompanied by 
increased egg abundance in dip-net samples in compari- 
son to previous samples. Gravid females and courting 
males were occasionally scanned for individual identi- 
fication with a PIT (passive intergrated transponder) 
reader when fish approached the surface. 
Analyses of spawning data 
Date and time of day, photoperiod, lunar phase, and 
tidal cycle were noted upon detection of a spawning 
event. Data were grouped by month, hour, and phase 
of the synodic month to determine seasonal, diel, and 
lunar spawning periodicities. Hourly spawning periodic- 
ity was analyzed in relation to sunset and to the 24-h 
clock after correcting to Pacific Standard Time (PST), 
without adjusting for daylight savings time. Water 
temperature was recorded to the nearest 0.15°C every 
hour at a depth of 3 m with an Optic Stowaway tem- 
perature logger (Onset Computer Corp., Pocasset, MA) 
suspended from the net pen. Continuous temperature 
data for the 2002 spawning season were obtained from 
a temperature logger at an adjacent net-pen site (300 m 
away) within Catalina Harbor. Additional temperature 
and salinity measurements were made upon detection 
of eggs with a YSI 85 instrument (YSI Inc., Yellow 
Springs, OH). 
Acoustic equipment 
Sounds were received with an omnidirectional hydro- 
phone (International Transducer Corporation 6050-C, 
Santa Barbara, CA) with an essentially flat frequency 
response between 50 Hz and 35 kHz. The hydrophone 
was powered by a custom 24-V power supply and ampli- 
fier with an incorporated reference tone (Frank Aubrey, 
Hubbs-SeaWorld Research Institute, San Diego, CA). 
Sounds were recorded with a PCM-M1 digital audio 
tape recorder (Sony Corp., Tokyo, Japan) set to a con- 
stant gain. 
Audio recordings 
Three-minute audio recordings were made at regular 
intervals with the hydrophone suspended at a depth of 3 
m in the center of the net pen. Evening sound recordings, 
taken on 17 sampling dates from March through July 
2003, were focused around periods of spawning activity, 
and individual recordings were made every 30 minutes 
from 1 hour before to 3 hours after sunset. Additional 
recordings were made every hour for 24 hours, once 
a month, on randomly selected dates from April 2003 
through March 2004 to document seasonal and diel 
sound patterns. No recordings occurred in February 
2004 because of extreme weather conditions. 
Acoustic analyses 
Sound recordings (n = 404) were digitally transferred to 
a PC hard drive for spectral analysis (SpectraPlus, vers. 
2.32.04, Pioneer Hill, Campbell, CA). Based on spectral 
characteristics, the following categories of white seabass 
sounds were noted: single pulse-trains, multiple pulse- 
trains, drum-rolls, thuds, abbreviated chants, spawning 
chants, or hydrodynamic booms as described in Aalbers 
and Drawbridge (in press). Sound production rates for 
each sound type were determined from each recording. 
