Locascio and Mann: Diel and seasonal timing of sound production by Pogonias cromis 
337 
during the peak spawning season of weakfish. They 
noted physiological indicators of reproductive readi- 
ness in weakfish, including increased plasma androgen 
levels and hypertrophy of sonic muscle in males, were 
evident during the seasonal period of maximal sound 
production and spawning. This pattern has also been 
documented for spotted seatrout ( Brown-Peterson, 2003) 
and toadfish (Fine and Pennymaker, 1986). It is likely 
that similar conditions exist in black drum and contrib- 
ute to earlier and increased sound production during 
the peak seasonal reproductive period. 
For each time series the ascending slope was sig- 
nificantly greater than the descending slope of cho- 
ruses. The more gradual changes associated with the 
descending slope of the chorus event may be due to 
fewer individuals calling. This may be a consequence 
of sonic muscle fatigue, but it may also be related to 
fluctuations in hormone levels, as demonstrated on a 
seasonal time frame for weakfish. Monthly mean val- 
ues of time of maximum SPL were not highly variable 
despite the relatively high variability in chorus start 
and end times. Rates of SPL change during chorus 
events are not available in the literature, although in 
cases where sufficient diel time series data have been 
collected authors have observed a relatively rapid onset 
of calling and substantial increase in SPL over moder- 
ately short time periods (Breder, 1968; Connaughton 
and Taylor 1995; Locascio and Mann, 2008; Mann et 
al., 2008). One mechanism for this increase in SPL 
may be that an individual’s calls elicit responses from 
other individuals and result in rapidly increased SPL 
as calling activity spreads throughout the network 
of fish. This mechanism has been proposed to serve 
as a means of aggregating individuals for spawning 
while creating the opportunity among (male) individu- 
als to compete acoustically for a chance at reproduc- 
tion. Some evidence indicates that calling rates of 
individuals are not highly variable (Connaughton and 
Taylor, 1995; Locascio, 2010) and therefore increased 
SPL and calling rates of a group may be due to more 
individuals calling, as opposed to individuals calling 
more (Connaughton and Taylor, 1995). More data are 
needed to understand how frequencies and sound levels 
and calling rates vary among individuals of a species. 
Variation in fundamental frequencies of black drum 
calls with body size has been shown by Tellechea et 
al. (2010). 
Conclusions 
This study revealed that the timing and amplitude of 
black drum sound production is strongly correlated with 
the seasonal spawning period described in the literature. 
Long-term acoustic recording systems can therefore be 
used to complement traditional methods for defining 
the spawning season, are much less expensive, and 
produce high-resolution time series data. These record- 
ing systems are an especially useful and cost-effective 
tool for exploring new and remote locations where the 
formation of spawning aggregations is suspected or for 
monitoring the recovery of historical spawning sites. 
Inferences about habitat quality can also be made from 
acoustic data because spawning site selection should 
place early life history stages in habitats beneficial 
for growth and survival (Peebles and Tolley, 1988). In 
order to advance the use of passive acoustic methods 
future studies must focus on establishing quantitative 
relationships between sound production and spawning, 
the number and biomass of spawning individuals, and 
environmental parameters. Also required is a more 
detailed understanding of the behavior associated with 
sound production and the identification of currently 
unidentified sound- producing species. 
Literature cited 
Aalbers, S. A. 
2008. Seasonal, diel, and lunar spawning periodicities 
and associated sound production of white seabass ( Atrac - 
toscion nobilis). Fish. Bull. 106:143—151. 
American National Standards Institute. 
1994. Acoustical terminology, 9 p. Standards Secretar- 
iat, Acoustical Soc. America, New York. ANSI-SI. 1-1994. 
Breder, C. M. 
1968. Seasonal and diurnal occurrences of fish sounds 
in a small Florida bay. Bull. Am. Mus. Nat. Hist. 
138:327-378. 
Brown-Peterson, N. 
2003. The reproductive biology of spotted seatrout. In 
The biology of seatrout (S. A. Bortone, ed.), p. 
99-133. CRC Press, Boca Raton, FL. 
Connaughton, M. A., and M. H. Taylor. 
1995. Seasonal and daily cycles in sound production 
associated with spawning in the weakfish, Cynoscion 
regalis. Environ. Biol. Fishes 42:233-240. 
Domeier, M. L., and P. L. Colin. 
1997. Tropical reef fish spawning aggregations: defined 
and reviewed. Bull. Mar. Sci. 60 698-726. 
Erisman, B. E., and T. H. Konotchick. 
2009. Observations of spawning in the leather bass, 
Dermatolepis dermatolepis (Teleostei: Epinephelidae), 
at Cocos Island, Costa Rica. Environ. Biol. Fishes 
85:15-20. 
Fine, M. L., and K. R. Pennymaker. 
1986. Hormonal basis for sexual dimorphism of the 
sound-producing apparatus of the oyster toadfish. Exp. 
Neurol. 92:289-298. 
Fitzhugh, G. R., B. A. Thompson, and T. G. Snider III. 
1993. Ovarian development, fecundity, and spawning 
frequency of black drum Pogonias cromis in Louisi- 
ana. Fish. Bull. 91:244-253. 
Gilmore, R. G., Jr. 
2003. Sound production and communication in the spot- 
ted seatrout. In Biology of the spotted Seatrout (S. A. 
Bortone, ed.), p. 177-195. CRC Press, Boca Raton, FL. 
Hoese, H. D., and R. H. Moore. 
1998. Fishes of the Gulf of Mexico, Texas, Louisiana 
and adjacent waters, 422 p. Texas A&M Univ. Press, 
College Station, TX. 
Holt, S. A., G. J. Holt, and L.Young-Abel. 
1988. A procedure for identifying sciaenid eggs. Contrib. 
Mar. Sci. (suppl.) 30:99-108. 
